servlet-Servlet链接数据库不成功—

Servlet链接数据库不成功

这里是service.xml的配置部分

    <Resource name="jdbc/webdb" auth="Container"
                type="javax.sql.DataSource"
                driverClassName="com.mysql.jdbc.Driver"
                url="jdbc:mysql://http://127.0.0.1:3306/webdb?characterEncoding=utf-8"
                username="root"
                password=""
                maxActive="200"
                maxIdle="50"
                maxWait="3000"
    />

发布于：2017.06.01 02:22

servlet 数据库

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: 麦维森

声望： 10

2个回答

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如果密码没有问题的话，就是“//http:”，url没有必要写这个吧

发布于：2017.06.01 03:23

评论 0 |

: 蘑菇小包子

声望： 35

url去掉 //heep: 试试

发布于：2017.06.01 04:00

评论 0 |

: 伪墨

声望： 200

: 插入链接

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servlet连接mysql数据库问题: 本人初学web组件，很多基础不会，望各位大神不要鄙视~~~~ -----login.java---- package com.tsinghua; import javax.servlet.http.*; import java.io.*; public class Login extends HttpServlet{ public void doGet(HttpServletRequest req,HttpServletResponse res){ //业务逻辑 try{ //接受用户名和密码 String u=req.getParameter("usrename"); String p=req.getParameter("passwd"); //中文乱码 res.setContentType("text/html;charset=gbk"); PrintWriter pw=res.getWriter(); pw.println("<html>"); pw.println("<body>"); pw.println("<form action=logincl method=post>"); pw.println("用户名：<input type=text name=username><br>"); pw.println("密码：<input type=password name=passwd><br>"); pw.println("<input type=submit value=Login><br>"); pw.println("</form>"); pw.println("</body>"); pw.println("</html>"); } catch(Exception ex){ ex.printStackTrace(); } } public void doPost(HttpServletRequest req,HttpServletResponse res){ this.doGet(req,res); } } ----loginCl.java---------- package com.tsinghua; import javax.servlet.http.*; import java.io.*; import java.sql.*; public class LoginCl extends HttpServlet{ public void doGet(HttpServletRequest req,HttpServletResponse res){ Connection ct=null; Statement sm=null; ResultSet rs=null; String host="127.0.0.1:3306"; try{ String u=req.getParameter("username"); String p=req.getParameter("passwd"); PrintWriter pw=res.getWriter(); Class.forName("com.mysql.jdbc.Driver"); ct=DriverManager.getConnection("jdbc:mysql://"+host+"/login","root","2535663"); sm=ct.createStatement(); rs=sm.executeQuery("select top 1 * from users where username='"+u+"'and passwd='"+p+"'"); pw.println("连接成功！"); if(rs.next()){ //合法 res.sendRedirect("welcome"); }else{ //不合法 res.sendRedirect("login"); } HttpSession hs=req.getSession(true); hs.setMaxInactiveInterval(30); hs.setAttribute("uname",u); } catch(SQLException e) { e.printStackTrace(); } catch(ClassNotFoundException e) { e.printStackTrace(); } catch(Exception ex){ ex.printStackTrace(); } finally{ try { if(rs!=null){ rs.close(); } if(sm!=null){ sm.close(); } if(ct!=null){ ct.close(); } }catch (Exception ex) { ex.printStackTrace(); } } } public void doPost(HttpServletRequest req,HttpServletResponse res){ this.doGet(req,res); } } ------wel.java------- package com.tsinghua; import javax.servlet.http.*; import java.io.*; import java.sql.*; public class wel extends HttpServlet{ public void doGet(HttpServletRequest req,HttpServletResponse res){ Connection ct=null; Statement sm=null; ResultSet rs=null; String host="127.0.0.1:3306"; try{ String u=req.getParameter("username"); String p=req.getParameter("passwd"); //从session中得到用户名 HttpSession hs=req.getSession(true); String myName=(String)hs.getAttribute("uname"); String name=""; String passwd=""; if(myName==null){ res.sendRedirect("login"); return ; } //解决中文乱码 res.setCharacterEncoding("gbk"); PrintWriter pw=res.getWriter(); pw.println("<body bgcolor=#CED3FF>"); pw.println("<img src=imgs/1.GIF>      欢迎您:"+myName+"<img src=imgs/me.gif><hr><center>"); pw.println("<h1>管理用户</h1>"); //做个超链接 pw.println("<br><a href=login>返回重新登录</a>"); 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Apache Tomcat/7.0.82 控制台:十月 26, 2017 1:10:55 上午 org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet [LoginServlet] in context with path [/xxbbs] threw exception java.lang.NullPointerException at com.xx.servlet.LoginServlet.doPost(LoginServlet.java:99) at javax.servlet.http.HttpServlet.service(HttpServlet.java:650) at javax.servlet.http.HttpServlet.service(HttpServlet.java:731) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:744) 不知道哪里出问题了，之前一直好好的，求大神帮我看看

Java web jdbc怎么连接数据库，要配置什么啊: 代码都已经打完了，但是一直连接不成功，sqlserver数据库驱动也下下来了并放到buding path里了，sqlserver协议tcp/ip也更改了，数据库也用用户名密码登陆了，还差什么啊，求大神指教，下面是代码，都是网上的，应该没错。 package com.demo; import java.io.*; import java.io.IOException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import javax.servlet.*; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.*; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class register */ @WebServlet("/register.do") public class register extends HttpServlet { public Connection cn; public PreparedStatement ps; public ResultSet rs; //连接数据库 public void getCn() { String url="jdbc:microsoft:sqlserver://192.168.1.119:1433;DatabaseName=Web"; String driverpath="com.microsoft.jdbc.sqlserver.SQLServerDriver"; String name="sa"; String pwd="123456"; try{ Class.forName(driverpath); cn=DriverManager.getConnection(url,name,pwd); if(cn!=null) { System.out.println("ok"); cn.close(); } else System.out.println("数据库连接失败！"); }catch(Exception e) { e.printStackTrace(); } } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().append("Served at: ").append(request.getContextPath()); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ //得到post资源 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=gbk"); PrintWriter out=response.getWriter(); String name=request.getParameter("username"); String pwd=request.getParameter("password"); System.out.println(name); System.out.println(pwd); if(this.insert(name,pwd)==true) { out.println("注册成功"); } else out.println("注册失败"); out.flush(); out.close(); } //注册添加数据 public boolean insert(String name,String pwd) { getCn(); boolean b=false; String sql="insert into login values(?,?)"; try{ ps=cn.prepareStatement(sql); ps.setString(1, name); ps.setString(2, pwd); ps.execute(); b=true; }catch(Exception e) { e.printStackTrace(); }finally { try{ if(rs!=null) rs.close(); else if(ps!=null) ps.close(); else if(cn!=null) cn.close(); }catch(Exception e){} } return b; } }

servlet 怎么把数据库查到的东西传到HTML中: 下面是我写的，不知道该怎么改了。。 package servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.Date; public class Servlet1 extends HttpServlet { private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 获取客户端发送的请求类型：GET/POST doPost(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub String responseBody = "Current request method is <B>:" + request.getMethod() + "</B> <br>" + new Date(); // 将所有HTML响应数据通过网络回发到客户端。 // 获取发送响应的PrintWriter对象 PrintWriter out = response.getWriter(); // 装在需要响应到客户端的响应数据 out.println(responseBody); try{ Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); //注册JDBC驱动 Connection con=DriverManager.getConnection("jdbc:sqlserver://localhost:1433;DatabaseName=Stu_Man","sa","13361775956"); //链接数据库 System.out.println("连接成功！"); //如果连接成功，控制台输出“连接成功！” //查询数据 String str2= "select Course.couid,counam, coutimes, couroom, courtea from Course,Student,Score where stunam ='张三' and Student.stuid=Score.stuid and Score.couid=Course.couid"; Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery(str2); response.setContentType("text/html;charset=utf-8"); while (rs.next()) { String a = rs.getString("couid"); String b = rs.getString("counam"); String c = rs.getString("coutimes"); String d = rs.getString("couroom"); String e = rs.getString("courtea"); out.print("<td><input type=\"checkbox\" name=\"id\" value=\""+a+"\"></td>"); out.print("<td>"+b+"</td>"); out.print("<td>"+c+"</td>"); out.print("<td>"+d+"</td>"); out.print("<td>"+e+"</td>"); out.print("</tr>"); } out.print("</table></center>"); out.println(" </BODY>"); out.println("</HTML>"); out.flush(); out.close(); //插入数据 String str1 = "insert into Student values(107,'王九','男','95-05-02','技术4')"; Statement stm = con.createStatement(); int res= stm.executeUpdate(str1); if (res > 0) { System.out.println("数据已成功插入！"); } //删除数据 PreparedStatement p = null; try { String str3 = "delete from Student where stunam ='王' "; p = con.prepareStatement(str3); int row = p.executeUpdate(); System.out.println("成功删除了"+row+"行数据!"); } catch (SQLException sqlE) { sqlE.printStackTrace(); } if (rs != null) { con.close(); //释放资源 } } catch (SQLException e) { // e.printStackTrace(); System.out.println("数据执行错误！"); } catch(Exception e) { System.out.println("连接失败！"); } // 发送响应 out.close(); } }

Java WEB 连接数据库的登录界面失败？: 连接数据库是成功的，但是输入用户名和密码后跳转到错误页面有几段代码不太确定对不对，请帮忙看一看 //login.jsp ``` <form name="form1" method="post" action="manager.do?action=login"> ``` //struts-config.xml ``` <action name="managerForm" path="/manager" scope="request" type="com.action.Manager" validate="true"> <forward name="managerLoginok" path="/main.jsp" /> <forward name="error" path="/error.jsp" /> </action> ``` //Manager.java ``` package com.action; import org.apache.struts.action.*; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.actionForm.ManagerForm; import com.dao.ManagerDAO; import javax.servlet.http.HttpSession; public class Manager extends Action { private ManagerDAO managerDAO = null; public Manager() { this.managerDAO = new ManagerDAO(); } public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) { String action = request.getParameter("action"); if (action == null || "".equals(action)) { return mapping.findForward("error"); } else if ("login".equals(action)) { return managerLogin(mapping, form, request, response); } request.setAttribute("error", "操作失败！"); return mapping.findForward("error"); } // 管理员身份验证 public ActionForward managerLogin(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) { ManagerForm managerForm = (ManagerForm) form; //将接收到的表单信息强制转换成ActionForm类型 managerForm.setAd_name(managerForm.getAd_name()); managerForm.setAd_pwd(managerForm.getAd_pwd()); int ret = managerDAO.checkManager(managerForm); System.out.print("验证结果ret的值:" + ret); if (ret == 1) { //将登录到系统的管理员名称保存到session HttpSession session = request.getSession(); session.setAttribute("manager", managerForm.getAd_name()); return mapping.findForward("managerLoginok"); } else { request.setAttribute("error", "您输入的管理员名称或密码错误！"); return mapping.findForward("error"); } } } ``` //ConnDB.java ``` //执行查询语句 public ResultSet executeQuery(String sql) { try { conn=getConnection(); stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY); rs=stmt.executeQuery(sql); } catch(SQLException ex){ System.err.println(ex.getMessage()); } return rs; } ``` //ManagerDAO.java ``` //管理员身份验证 public int checkManager(ManagerForm managerForm) { int flag = 0; ChStr chStr=new ChStr(); String sql = "SELECT * FROM Ad_info where ad_name='" + chStr.filterStr(managerForm.getAd_name()) + "'"; ResultSet rs = conn.executeQuery(sql); try { if (rs.next()) { String pwd = chStr.filterStr(managerForm.getAd_pwd()); //获取输入的密码并过滤输入字符串中的危险字符 if (pwd.equals(rs.getString(3))) { flag = 1; } else { flag = 0; } }else{ flag = 0; } } catch (SQLException ex) { flag = 0; }finally{ conn.close(); } return flag; } ``` 大概应该是这几段代码的原因，但是不清楚应该怎么修改，请帮忙看一下

jdbc连接数据库，可以加载驱动，数据库内却取不到值(NullPointException)？: 我用两种途径连接数据库，一种是：<br> ![图片说明](https://img-ask.csdn.net/upload/201911/04/1572862039_634364.png)<br> 这一种应该没问题 <br><br> 但是在另一种途径遇到了以下问题：<br> ![图片说明](https://img-ask.csdn.net/upload/201911/04/1572862594_438226.jpg)<br><br> //以下是异常信息：第一次提问，请问还需要什么信息orz <br><br> ----------------- 换了个电脑代码进行修改之后项目能够正常运行了在原来的电脑上仍有以下报错： ```java 数据库驱动加载成功！ Exceptionconn java.lang.NullPointerException findall failed at javax.xml.bind.DatatypeConverter.parseHexBinary(DatatypeConverter.java:310) at com.microsoft.sqlserver.jdbc.SQLServerConnection.sendLogon(SQLServerConnection.java:4061) at com.microsoft.sqlserver.jdbc.SQLServerConnection.logon(SQLServerConnection.java:3157) at com.microsoft.sqlserver.jdbc.SQLServerConnection.access$100(SQLServerConnection.java:82) at com.microsoft.sqlserver.jdbc.SQLServerConnection$LogonCommand.doExecute(SQLServerConnection.java:3121) at com.microsoft.sqlserver.jdbc.TDSCommand.execute(IOBuffer.java:7151) at com.microsoft.sqlserver.jdbc.SQLServerConnection.executeCommand(SQLServerConnection.java:2478) at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:2026) at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:1687) at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:1528) at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:866) at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:569) at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677) at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228) at ch04.utils.BookUtils.getConnection(BookUtils.java:20) at ch04.dao.impl.BookDaoImpl.findByAll(BookDaoImpl.java:88) at ch04.service.impl.BookservicesImpl.findByAll(BookservicesImpl.java:38) at ch04.controller.BookAction.showall(BookAction.java:127) at ch04.controller.BookAction.doPost(BookAction.java:46) at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.base/java.lang.Thread.run(Thread.java:835) java.lang.NullPointerException at ch04.dao.impl.BookDaoImpl.findByAll(BookDaoImpl.java:92) at ch04.service.impl.BookservicesImpl.findByAll(BookservicesImpl.java:38) at ch04.controller.BookAction.showall(BookAction.java:127) at ch04.controller.BookAction.doPost(BookAction.java:46) at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.base/java.lang.Thread.run(Thread.java:835) [] ```

Java与数据库连接成功后: jsp输入框input,输入数据如何与servlet交互实现模糊查询

初学jsp遇到数据库连接处理问题: 这个是注册插入数据代码，在网页中可以运行成功，说明我的数据库连接是没问题的 ``` <%String uid=request.getParameter("uid"); String pwd=request.getParameter("pwd"); Object[]paramss={uid,pwd}; String sqll="insert into tb_vip values(?,?)"; if(DBHelper.runupdatesql(sqll, paramss)) { out.print("已经成功注册"); } else out.print("服务器问题请与客服联系"); %> ``` 下面这段是判断数据库中用户名是否存在，不存在才可以用上面代码注册，但是运行后不管数据库中是否存在用户名，网页中只打印“注册失败，用户名不存在” ``` <% String uid=request.getParameter("uid"); String pwd=request.getParameter("pwd"); Object[] params={uid}; String sql ="select count(*)from tb_vip where userid=?"; Result result=DBHelper.runselectsql(sql, params); if(result.getRowCount()==0){ Object[]paramss={uid,pwd}; String sqll="insert into tb_vip values(?,?)"; if(DBHelper.runupdatesql(sqll, paramss)){ out.print("已经成功注册"); }else{out.print("服务器问题请与客服联系");}} else{ out.print("注册失败,用户名已存在"); } %> ``` 下面是java数据库处理代码部分 ``` package jspex; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import javax.servlet.jsp.jstl.sql.Result; import javax.servlet.jsp.jstl.sql.ResultSupport; public class DBHelper { private static final String className = "com.microsoft.sqlserver.jdbc.SQLServerDriver"; private static final String url = "jdbc:sqlserver://localhost:1433;databasename=studentm"; private static final String uname = "sa"; private static final String upass = "c111111"; public static Connection getConn(){ Connection conn = null; try{ Class.forName(className); conn = DriverManager.getConnection(url,uname, upass); } catch(Exception e){ e.printStackTrace(); } return conn; } public static void closeConn(Connection conn){ try{ if(conn!=null){ conn.close(); } } catch(Exception e){ e.printStackTrace(); } } public static void closePstmt(PreparedStatement pstmt){ try{ if(pstmt!=null){ pstmt.close(); } } catch(Exception e){ e.printStackTrace(); } } public static void closeRs(ResultSet rs){ try{ if(rs!=null){ rs.close(); } } catch(Exception e){ e.printStackTrace(); } } public static boolean runupdatesql(String sql,Object[]params){ Connection con=null; PreparedStatement ps=null; try{ con=getConn(); ps=con.prepareStatement(sql); for(int i=0;i<params.length;i++){ ps.setObject(i+1, params[i]); } ps.executeUpdate(); return true; }catch(Exception e){ e.printStackTrace(); return false; } finally{ try{ ps.close(); con.close(); } catch(Exception e){ e.printStackTrace(); } } } public static Result runselectsql(String sql,Object[]params){ Connection con=null; PreparedStatement ps=null; ResultSet res=null; Result result=null; try{ con=getConn(); ps=con.prepareStatement(sql); for(int i=0;i<params.length;i++){ ps.setObject(i+1, params[i]); } res=ps.executeQuery(); result=ResultSupport.toResult(res); } catch(Exception e){ e.printStackTrace(); } finally{ try{ res.close(); ps.close(); con.close(); }catch(Exception e){ e.printStackTrace(); } } return result; } } ``` 下面是注册页面，我为了好找错误，还把相关js功能注释掉了 ``` <html> <head> <title>reg</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <style type="text/css"> #loginform{ width:300px; height:auto; } label{ width:60px; height:30px; text-align:left; font-size:14px; font-weight:hold; vertical-align:bottom; } .inpute{ width:160px; height:20px; } .row{ width:300px; height:30px; } </style> <script type="text/javascript"> function checkform(){ var name=document.getElementById("uid"); var pass=document.getElementById("pwd"); /*var rpass=document.getElementById("rpwd");*/ if(name.value.length<=0){ alert("用户名不能为空"); name.focus(); return false; } if(pass.value.length>=8){ alert("密码长度不对"); pass.focus(); return false; } /**if(pass!=rpass){ alert("密码不一致"); return false; }**/ return true; } </script> </head> <body> <div id="loginform"> <form onsubmit="return checkform();"action="doreg.jsp" method="post"> <div class="row"> <label for="uid">用户名： </label> <input name="uid" type="text" class="inpute" id="uid"> </div> <div class="row"> <label for="pwd">密码： </label> <input name="pwd" type="password" class="inpute" id="pwd"> </div> </div>  <div class="row"> <input type="submit" value="注册"/><input type="reset" value="重新填写"/> </div> </form> </div> </body> </html> ``` 分析了很久，不知道出现了什么问题，希望大家可以帮帮我

数据库连接时总是空指针异常？测试表单信息无误，就是查询数据库时出错: java.lang.NullPointerException at com.Users.LoginServlet.doPost(LoginServlet.java:58) at javax.servlet.http.HttpServlet.service(HttpServlet.java:154) at javax.servlet.http.HttpServlet.service(HttpServlet.java:92) at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:106) at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:173) at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229) at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:274) at com.caucho.server.port.TcpConnection.run(TcpConnection.java:514) at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:527) at com.caucho.util.ThreadPool.run(ThreadPool.java:449) at java.lang.Thread.run(Unknown Source) 源代码： package com.Users; import java.io.IOException; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import com.Service.LoginService; /** * 登录控制层： LoginServlet * 将用户个人信息保存到 Session范围内 * 根据status对页面进行分别显示 * @author daichen * */ public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; /* * 注入 LoginService 服务 */ private LoginService loginService; @Override protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { doGet(req,res); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("GBK"); response.setCharacterEncoding("GBK"); User user = null; // 获取表单提交的登录信息 String userId = null; String password = null; userId = request.getParameter("userId"); password = request.getParameter("password"); // 先判断用户信息是否否为空 if(userId == null || "".equals(userId) || password == null || "".equals(password)) { // 用户信息有误 , 回到 login.jsp 页面 response.getWriter().println("<html><h3><font color='#f00'>对不起，你输入的信息有误 .请重新确认！</h3></font></html>"); return; } else { // 到数据表 user 中查找该用户 , 返回一个 User 对象 System.out.println(userId+" "+password); user = loginService.userLogin(userId,password); // 并对查询到的结果进行处理 if(user != null) { // 获取请求域的session对象 HttpSession session = request.getSession(); // 对三种权限分开添加到 Session 域中 if(user.getStatus() == 0){ session.setAttribute("geneUser", user); } if(user.getStatus() == 1){ session.setAttribute("admin", user); } if(user.getStatus() == 2){ session.setAttribute("superAdmin", user); } // 成功获取到用户信息 , 转到 index.jsp RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/jsp/index.jsp"); rd.forward(request, response); return; } else { // 查询没有该用户 , 转到 login.jsp response.getWriter().print("<h3><font color='#f00'>对不起，你还未注册用户 </h3></font>" + userId + "<h3><font color='#f00'>请先前去注册！</h3></font>"); RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/jsp/register.jsp"); rd.forward(request, response); return; } } } }

前端与数据库进行数据交互: 你给的网站我去做了一下，贴个地址<br>https://www.cnblogs.com/jsonphp/articles/6517343.html<br>所有代码都是原封不动输进去的。（当然数据库是我自己的）<br> 连接数据库成功，所有代码IDEA提示没有输入错误。<br>启动tomcat服务后出现如下情况![图片说明](https://img-ask.csdn.net/upload/201904/22/1555948137_860888.png) <br>鼠标点上去之后出现这个提示：error during artifact deployment<br>然后我点了一下这个圈圈，![图片说明](https://img-ask.csdn.net/upload/201904/22/1555948216_788182.png) <br>它变成了这个样子![图片说明](https://img-ask.csdn.net/upload/201904/22/1555948291_824212.png)<br>我自己新建了一个新项目什么都没写，tomcat服务可以运行，我把本项目的web.xml文件内所有额外添加的代码全部删除，tomcat服务可以运行，可以显示index.jsp页面，但页面跳转失败，404。我的IDEA是最新版本，你给我的项目作者说了这样一句话：使用过滤器，要引入jar包：servlet-2_5-api.jar但我引入这个包之后代码反而会报错! ![图片说明](https://img-ask.csdn.net/upload/201904/22/1555948790_167605.png) <br> 请问我哪里操作错了吗，调试一下午了，原封不动的代码都不运行不出来真的很难受。

MySQL数据库连接问题。: [code="java"][/code]我是个Java开发的初学者，最近开始自学Servlet/JSP编程，参考的是孙鑫老师编的《Servlet/Jsp深入详解——基于Tomcat的Web开发》。在学习“第4章数据库访问”时遇到了问题，我按照书上的代码编写了一个CreateDBServlet.java用于连接数据库，编译是没问题的。进行了部署和配置后，访问时出错了，浏览器显示的错误信息如下： HTTP Status 500 - -------------------------------------------------------------------------------- type Exception report message description The server encountered an internal error () that prevented it from fulfilling this request. exception javax.servlet.ServletException: java.sql.SQLException: Access denied for user 'root'@'localhost' (using password: NO) org.sunxin.ch04.servlet.CreateDBServlet.doGet(CreateDBServlet.java:61) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) root cause java.sql.SQLException: Access denied for user 'root'@'localhost' (using password: NO) com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055) com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956) com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491) com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423) com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:910) com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3923) com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1273) com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2031) com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:718) com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:298) com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282) java.sql.DriverManager.getConnection(DriverManager.java:525) java.sql.DriverManager.getConnection(DriverManager.java:171) org.sunxin.ch04.servlet.CreateDBServlet.doGet(CreateDBServlet.java:44) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) note The full stack trace of the root cause is available in the Apache Tomcat/6.0.18 logs. -------------------------------------------------------------------------------- Apache Tomcat/6.0.18 CreateDBServlet代码如下： [code="java"]package org.sunxin.ch04.servlet; import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class CreateDBServlet extends HttpServlet { private String userUrl; private String userName; private String password; public void init() throws ServletException { String driverClass=getInitParameter("driverClass"); userUrl=getInitParameter("userUrl"); userName=getInitParameter("userName"); password=getInitParameter("password"); try { Class.forName(driverClass); } catch (ClassNotFoundException ce) { throw new ServletException("加载数据库驱动失败！"); } } public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException { Connection conn=null; Statement stmt=null; try { conn=DriverManager.getConnection(userUrl,userName,password); stmt=conn.createStatement(); stmt.executeUpdate("create database bookstore"); stmt.executeUpdate("use bookstore"); stmt.executeUpdate("create table bookinfo(id INT not null primary key,title VARCHAR(50) not null,author VARCHAR(50) not null,bookconcern VARCHAR(50) not null,publish_date DATE not null,price FLOAT(4,2) not null,amount SMALLINT,remark VARCHAR(200))ENGINE=InnoDB"); stmt.addBatch("insert into bookinfo values(1,'Java Web 详解','孙鑫','电子工业出版社','2006-4-20',99.00,35,null)"); stmt.addBatch("insert into bookinfo values(2,'Struts 2深入详解','孙鑫','电子工业出版社','2008-6-15',79.00,20,null)"); stmt.addBatch("insert into bookinfo values(3,'Servlet/JSP详解','孙鑫','电子工业出版社','2008-7-1',79.00,10,null)"); stmt.executeBatch(); resp.setContentType("text/html;charset=GBK"); PrintWriter out=resp.getWriter(); out.println("数据库创建成功！"); out.close(); } catch (SQLException se) { throw new ServletException(se); } finally { if(stmt!=null) { try { stmt.close(); } catch (SQLException se) { se.printStackTrace(); } stmt=null; } if(conn!=null) { try { conn.close(); } catch (SQLException se) { se.printStackTrace(); } conn=null; } } } }[/code] web.xml文件如下： [code="java"]<?xml version="1.0" encoding="gb2312"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <servlet> <servlet-name>createDB</servlet-name> <servlet-class>org.sunxin.ch04.servlet.CreateDBServlet</servlet-class> <init-param> <param-name>driverClass</param-name> <param-value>com.mysql.jdbc.Driver</param-value> </init-param> <init-param> <param-name>userUrl</param-name> <param-value>jdbc:mysql://localhost:3306</param-value> </init-param> <init-param> <param-name>userName</param-name> <param-value>root</param-value> </init-param> <init-param> <param-name>passord</param-name> <param-value>12345678</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>createDB</servlet-name> <url-pattern>/createdb</url-pattern> </servlet-mapping> </web-app> [/code]

我用的是纯驱动连接SQL server数据库，运行的时候显示第128行错误，不知道怎么改。求帮助。: package servlets; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import java.sql.*; import toolbean.*; public class regservlet extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response);} /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=gbk"); PrintWriter out = response.getWriter(); ValueBean vb=new ValueBean(); vb.setUsername(MyTools.toChinese(request.getParameter("username"))); vb.setUserpass(request.getParameter("userpass")); vb.setBirthdate(request.getParameter("birthdate")); vb.setGender(MyTools.toChinese(request.getParameter("gender"))); vb.setNativeplace(MyTools.toChinese(request.getParameter("nativeplace"))); vb.settype(MyTools.toChinese(request.getParameter("type"))); String url="jdbc:sqlserver://127.0.0.1:1433;DataBaseName=lkk"; String user="root"; String pwd="123"; String sql=""; Connection conn=null; Statement stmt=null; ResultSet rs=null; try{ sql="select username from user where username='"+vb.getUsername()+"'"; conn=DriverManager.getConnection(url, user, pwd); stmt=conn.createStatement(); rs=stmt.executeQuery(sql); HttpSession session=request.getSession(); if(rs.next()){ PrintWriter pw=response.getWriter(); pw.write("<script language='javascript'>alert('用户名已存在，请重新注册')</script>"); response.sendRedirect("reg.jsp?err=1"); }else{ StringBuffer newsql=new StringBuffer(); newsql.append("insert into user (username,userpass,gender,birthdate,nativeplace,type) values ('"); newsql.append(vb.getUsername()); newsql.append("','"); newsql.append(vb.getUserpass()); newsql.append("','"); newsql.append(vb.getGender()); newsql.append("','"); newsql.append(vb.getBirthdate()); newsql.append("','"); newsql.append(vb.getNativeplace()); newsql.append("','"); newsql.append("会员"); newsql.append("')"); stmt.executeUpdate(newsql.toString()); session.setAttribute("msg_ok","注册成功！"); session.setAttribute("username",vb.getUsername()); response.sendRedirect("regMsg.jsp"); } }catch(Exception e){ out.print(e.toString()); }finally{ try{rs.close();}catch(Exception ee){} try{stmt.close();}catch(Exception ee){} try{conn.close();}catch(Exception ee){} } } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occure */ public void init() throws ServletException { try{ Class.forName("com.microsoft.jdbc.SQLServerDriver"); }catch (Exception e){ throw new ServletException("加载数据库驱动失败!");//这是第128行 } }} 错误描述： javax.servlet.ServletException: 加载数据库驱动失败! servlets.regservlet.init(regservlet.java:128) javax.servlet.GenericServlet.init(GenericServlet.java:212) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261) org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844) org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581) org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447) java.lang.Thread.run(Thread.java:619)

连接oracle时候报空指针异常: try { String className = "oracle.jdbc.driver.OracleDriver"; Class.forName(className); System.out.println("加载数据库驱动成功!"); } catch (ClassNotFoundException e) { System.out.println("加载数据库驱动失败!"); e.printStackTrace(); } try { System.out.println("开始连接数据库"); String user = "sys as sysdba"; String password = "123123"; String url = "jdbc:oracle:thin:@焱:1521:XE"; con = DriverManager.getConnection(url, user, password); System.out.print(con); System.out.println("创建数据库连接成功!"); } catch (SQLException e) { System.out.print(con); System.out.println("创建数据库连接失败!"); con = null; e.printStackTrace(); } 如果直接在类里面使用main函数获取数据库能够连接成功，取出数据，但是在web页面的servlet中使用DBManager dbm = new DBManager(); 就会报空指针异常 java.lang.NullPointerException java.lang.String.<init>(String.java:166) oracle.sql.CharacterSet.AL32UTF8ToString(CharacterSet.java:1516) oracle.jdbc.driver.DBConversion.CharBytesToString(DBConversion.java:588) oracle.jdbc.driver.DBConversion.CharBytesToString(DBConversion.java:541) oracle.jdbc.driver.T4CTTIoauthenticate.receiveOauth(T4CTTIoauthenticate.java:815) oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:361) oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:413) oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:164) oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:34) oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:752) java.sql.DriverManager.getConnection(DriverManager.java:664) java.sql.DriverManager.getConnection(DriverManager.java:247) util.DBManager.<init>(DBManager.java:33) service.StudentService.stu_Login(StudentService.java:21) MyServlet.LoginPageServlet.doPost(LoginPageServlet.java:35) javax.servlet.http.HttpServlet.service(HttpServlet.java:644) javax.servlet.http.HttpServlet.service(HttpServlet.java:725) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 最后指向的就是 con = DriverManager.getConnection(url, user, password);这一句连接语句

删除实现不了，数据库已经连上了: at com.wyk.ConnDB.executeUpdata(ConnDB.java:67) at org.apache.jsp.goods_005fdelete_jsp._jspService(goods_005fdelete_jsp.java:81) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) package com.wyk; import java.io.InputStream; import java.sql.*; import java.util.Properties; public class ConnDB { public Connection conn = null; public Statement stmt = null; public ResultSet rs = null; private static Statement st = null; //设置Statement类的对象 private static String propFileName = "/com/connDB.properties"; //指定资源文件保存的位置 private static Properties prop = new Properties(); private static String dbClassName ="com.mysql.jdbc.Driver"; private static String dbUrl = "jdbc:mysql://127.0.0.1:3306/db_wuliu?user=root&password=mysql&useUnicode=true"; public ConnDB(){ try { InputStream in=getClass().getResourceAsStream(propFileName); prop.load(in); //通过输入流对象加载Properties文件 dbClassName = prop.getProperty("DB_CLASS_NAME"); //获取数据库驱动 dbUrl = prop.getProperty("DB_URL", "jdbc:mysql://127.0.0.1:3306/db_wuliu?user=root&password=mysql&useUnicode=true"); } catch (Exception e) { e.printStackTrace(); //输出异常信息 } } public static Connection getConnection() { Connection conn = null; try { Class.forName(dbClassName).newInstance(); conn = DriverManager.getConnection(dbUrl); } catch (Exception ee) { ee.printStackTrace(); } if (conn == null) { System.err.println( "警告: DbConnectionManager.getConnection() 获得数据库链接失败.\r\n\r\n链接类型:" + dbClassName + "\r\n链接位置:" + dbUrl); } return conn; } /* * 功能：执行查询语句 */ public ResultSet executeQuery(String sql) { try { conn = getConnection(); stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY); rs = stmt.executeQuery(sql); } catch (SQLException ex) { System.err.println(ex.getMessage()); } return rs; } /* * 功能:执行更新操作 */ public boolean executeUpdata(String sql) { try { st = conn.createStatement(); //创建声明对象连接 ((ConnDB) st).executeUpdata(sql); //执行添加、修改、删除操作 return true; //如果执行成功则返回true } catch (Exception e) { e.printStackTrace(); return false; //如果执行成功则返回false }} /* * 功能:关闭数据库的连接 */ public void close() { try { if (rs != null) { rs.close(); } if (stmt != null) { stmt.close(); } if (conn != null) { conn.close(); } } catch (Exception e) { e.printStackTrace(System.err); } } }

java servlet的一个作业题.麻烦各位帮忙解决: ** 1.配置本地端口号为99992. 提供留言页面，包括，标题，留言类型，内容提交到serlvet中进行处理、如果必填项为空，跳转重新让用户输入。留言信息完整保存到数据库中，并跳转成功页面，提示用户留言成功。addNote.jsp 增加留言的JSPReceiveNotServlet.java 接收留言信息的servletNote.java 留言实体对象Dbconnection.java 连接数据库并保存留言Success.jsp 成功页面要求不可以使用数据库连接池留言页面需要有JS验证，标题如果为空不允许提交 3.不使用eclipse，手动放置一个应用名称为"manalapp"的应用。该应用为作业2的功能。并独立运行总共三问.谢谢各位高手帮助. ------------------------------------------------------------------------ **

数据库连接未能成功超过允许的获取尝试的最大数量（30）？: eclipse下创建Java项目测试过，c3p0可以正常获取连接。创建web项目，访问时报错，同意的c3p0配置文件 <property name="jdbcUrl">jdbc:mysql://localhost:3306/mydb1</property> <property name="driverClass">com.mysql.jdbc.Driver</property> <property name="user">root</property> <property name="password">localhost</property>  <property name="acquireIncrement">3</property> <property name="initialPoolSize">10</property> <property name="minPoolSize">2</property> <property name="maxPoolSize">10</property> </default-config> 控制台报错如下；警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@5a71b12e -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@236a9ecb -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet [UserServlet] in context with path [/bookstore3] threw exception java.lang.RuntimeException: java.lang.reflect.InvocationTargetException at cn.itcast.servlet.BaseServlet.service(BaseServlet.java:61) at javax.servlet.http.HttpServlet.service(HttpServlet.java:728) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at cn.itcast.servlet.BaseServlet.service(BaseServlet.java:45) ... 17 more Caused by: java.lang.RuntimeException: java.sql.SQLException: Connections could not be acquired from the underlying database! at cn.itcast.bookstore.user.dao.UserDao.findByUsername(UserDao.java:30) at cn.itcast.bookstore.user.service.UserService.regist(UserService.java:21) at cn.itcast.bookstore.user.web.servlet.UserServlet.regist(UserServlet.java:159) ... 22 more Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database! at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:615) at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128) at cn.itcast.jdbc.JdbcUtils.getConnection(JdbcUtils.java:43) at cn.itcast.jdbc.TxQueryRunner.query(TxQueryRunner.java:22) at cn.itcast.bookstore.user.dao.UserDao.findByUsername(UserDao.java:28) ... 24 more Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source. at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1406) at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:594) at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:514) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:681) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:608) ... 28 more 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@18d42a08 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@1f57ca86 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@fb4cb7e -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@191942d9 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@4283b70f -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@679614ff -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@2f366294 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:13:33 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:14:03 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@30e8bb73 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620) 十一月 14, 2018 8:14:03 下午 com.mchange.v2.resourcepool.BasicResourcePool forceKillAcquires 警告: Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@7df8f9f6 is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests. 十一月 14, 2018 8:14:03 下午 com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask run 警告: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@2707230c -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client at sun.reflect.GeneratedConstructorAccessor14.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:919) at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4004) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1284) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2312) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2122) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:774) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49) at sun.reflect.GeneratedConstructorAccessor16.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:375) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:289) at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:152) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1074) at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1061) at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1796) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:620)

Servlet遇到java.lang.NullPointerException问题无法解决，恳求帮助: 各位大佬，最近用Jsp+servlet写教务管理系统，其中servlet端有一个问题始终无法解决 ``` 严重: Servlet.service() for servlet [com.jwglxt.data.searchStudent] in context with path [/jwglxt] threw exception java.lang.NullPointerException ``` 目的是根据从前台传来的查询类型和查询关键词在数据库中进行检索，目前前后端数据传递正常，NullPointerException这个问题始终得不到解决，尝试了很多办法都不行，恳请各位大佬施以援手！代码如下： ```java package com.jwglxt.data; import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.SQLException; import java.sql.Statement; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; //思路：绑定一个弹出框在“搜索”按钮上，弹出框里放置一个datagrid,url为searchStudent @WebServlet("/searchStudent") public class searchStudent extends HttpServlet { @SuppressWarnings({ "null", "null", "null" }) protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置编码格式 request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("utf-8"); response.setContentType("text/json; charset=utf-8"); //获取学生信息主码-学号（sno） String name=request.getParameter("name"); System.out.println("搜索类型:"+name); String value=request.getParameter("value"); System.out.println("搜索值:"+value); //姑且赋值 /*String name="sno"; String value="990101";*/ //连接数据库 Connection connection=null; String driverName="com.microsoft.sqlserver.jdbc.SQLServerDriver";//SQL数据库引擎 String dbURL="jdbc:sqlserver://localhost:1433;DatabaseName=tjl";//数据源！！！注意若出现加载或者连接数据库失败一般是这里出现问题 String Name="sa"; String Pwd="19990713"; ResultSet rs=null; String sql="sql"; //定义JSON数组，用于保存从数据库查出来的数据 JSONArray array = new JSONArray(); try { Class.forName(driverName); connection=DriverManager.getConnection(dbURL,Name,Pwd); System.out.println("搜索学生:连接数据库成功"); } catch (ClassNotFoundException e2) { e2.printStackTrace(); }catch (SQLException e) { e.printStackTrace(); } //处理搜索类型尝试switch语句 /*switch(name) { case "sno":{ try { sql="select * from student where sno=?"; connection.prepareStatement(sql); pstmt.setString(1,value); //rs=pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); };break; }//case }//switch */ //处理搜索类型尝试If语句 if(name!=null) { if("sno".equals(name)){ try { //仅构造SQL语句，暂不运行 sql="select * from student where sno=?"; PreparedStatement pstmt=connection.prepareStatement(sql); pstmt.setString(1,value); rs = pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } } else if("sname".equals(name)){ try { //仅构造SQL语句，暂不运行 sql="select * from student where sname=?"; PreparedStatement pstmt=connection.prepareStatement(sql); pstmt.setString(1,value); rs = pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } } else if("sex".equals(name)){ try { //仅构造SQL语句，暂不运行 sql="select * from student where sex=?"; PreparedStatement pstmt=connection.prepareStatement(sql); pstmt.setString(1,value); rs = pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } } else if("dno".equals(name)){ try { //仅构造SQL语句，暂不运行 sql="select * from student where dno=?"; PreparedStatement pstmt=connection.prepareStatement(sql); pstmt.setString(1,value); rs = pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } } else { try { //仅构造SQL语句，暂不运行 sql="select * from student where dormno=?"; PreparedStatement pstmt=connection.prepareStatement(sql); pstmt.setString(1,value); rs = pstmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } } System.out.println(sql); } try { // 获取列数 ResultSetMetaData metaData = rs.getMetaData(); int columnCount = metaData.getColumnCount(); while (rs.next()) { JSONObject jsonObj = new JSONObject(); // 遍历每一列 for (int i = 1; i <= columnCount; i++) { String columnName =metaData.getColumnLabel(i); String value2 = rs.getString(columnName); try { jsonObj.put(columnName, value2); } catch (JSONException e) { // TODO Auto-generated catch block e.printStackTrace(); } } array.put(jsonObj); } } catch (SQLException e1) { e1.printStackTrace(); } //关闭 try { if(rs!=null) rs.close(); //pstmt.close(); connection.close(); } catch (SQLException e) { e.printStackTrace(); } //PrintWriter out = response.getWriter(); System.out.println(array); }//总类 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } public static void main(String args[]) { searchStudent ss=new searchStudent(); try { ss.doGet(null, null); } catch (ServletException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } ```

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阿里面试，面试官没想到一个ArrayList，我都能跟他扯半小时: 我是真的没想到，面试官会这样问我ArrayList。

曾经优秀的人，怎么就突然不优秀了。: 职场上有很多辛酸事，很多合伙人出局的故事，很多技术骨干被裁员的故事。说来模板都类似，曾经是名校毕业，曾经是优秀员工，曾经被领导表扬，曾经业绩突出，然而突然有一天，因为种种原因，被裁员了，...

大学四年因为知道了这32个网站，我成了别人眼中的大神！: 依稀记得，毕业那天，我们导员发给我毕业证的时候对我说“你可是咱们系的风云人物啊”，哎呀，别提当时多开心啦????，嗯，我们导员是所有导员中最帅的一个，真的???? 不过，导员说的是实话，很多人都叫我大神的，为啥，因为我知道这32个网站啊，你说强不强????，这次是绝对的干货，看好啦，走起来！ PS：每个网站都是学计算机混互联网必须知道的，真的牛杯，我就不过多介绍了，大家自行探索，觉得没用的，尽管留言吐槽吧???? 社...

良心推荐，我珍藏的一些Chrome插件: 上次搬家的时候，发了一个朋友圈，附带的照片中不小心暴露了自己的 Chrome 浏览器插件之多，于是就有小伙伴评论说分享一下我觉得还不错的浏览器插件。我下面就把我日常工作和学习中经常用到的一些 Chrome 浏览器插件分享给大家，随便一个都能提高你的“生活品质”和工作效率。 Markdown Here Markdown Here 可以让你更愉快的写邮件，由于支持 Markdown 直接转电子邮...

【程序人生】程序员接私活常用平台汇总: 00. 目录文章目录00. 目录01. 前言02. 程序员客栈03. 码市04. 猪八戒网05. 开源众包06. 智城外包网07. 实现网08. 猿急送09. 人人开发10. 开发邦11. 电鸭社区12. 快码13. 英选14. Upwork15. Freelancer16. Dribbble17. Remoteok18. Toptal19. AngelList20. Topcoder21. ...

看完这篇HTTP，跟面试官扯皮就没问题了: 我是一名程序员，我的主要编程语言是 Java，我更是一名 Web 开发人员，所以我必须要了解 HTTP，所以本篇文章就来带你从 HTTP 入门到进阶，看完让你有一种恍然大悟、醍醐灌顶的感觉。最初在有网络之前，我们的电脑都是单机的，单机系统是孤立的，我还记得 05 年前那会儿家里有个电脑，想打电脑游戏还得两个人在一个电脑上玩儿，及其不方便。我就想为什么家里人不让上网，我的同学 xxx 家里有网，每...