凌爷的手指 2019-05-20 22:39 采纳率: 0%
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login.jsp登录时报错有空指针

login.jsp登录时报错: Servlet.service() for servlet [LoginServlet] in context with path [/Course] threw exception java.lang.NullPointerException
package cn.hh.DB;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class JDBCKit
{
private static final String driverName="com.mysql.jdbc.Driver";
private static final String url="jdbc:mysql://127.0.0.1:3306/Hospital";
private static final String user="root";
private static final String password="0000000";

/**
 * 
 * @return
 */

@SuppressWarnings("unused")
public static Connection getConnection() {
    Connection conn=null;
    java.sql.Statement stmt = null;
    try {
        Class.forName(driverName);
        }
        catch (ClassNotFoundException e) 
           {
        e.printStackTrace();
            }
        try {
        conn = DriverManager.getConnection(url, user, password);
        stmt = conn.createStatement();
        return conn;
        }
     catch (Exception e) {
        e.printStackTrace();

    }
    return conn;
}

/**
 * 
 * @param rs
 * @param pstmt
 * @param conn
 */
public static void release(ResultSet rs, PreparedStatement pstmt, Connection conn) {
    try {
        if(rs != null) {
            rs.close();
        }
        if(pstmt != null) {
            pstmt.close();
        }
        if(conn != null) {
            conn.close();
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

}

login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
   <script type="text/javascript">
        function check(form) {
            var username = form.username.value;
            var password = form.password.value;
            if(username.length == 0 || password.length == 0) {
                alert('用户名或密码未填写，请检查.');
                return false;
            }
            if(username=="user"&&password=="pass")
                { 
                alert('欢迎您.'+username);
                session.setAttribute("loginUsername", username);
                session.setAttribute("loginUser",username);
                response.getRequestDispatcher("success.jsp").forward(request, response);
                }

            else {

                return true;
            }
        }
    </script>
<form action="/Course/login" method="post" onsubmit="return check(this)">
        账号：<input type="text" name="username"><br>
        密码：<input type="password" name="password"><br>
        <input type="submit" value="登录"><br>
</form>
 <c:if test="${requestScope.error != null}">
        <span style="color: red">${error} </span><br>
    </c:if>
</body>
</html>

package cn.hh.Dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import cn.hh.DB.JDBCKit;

public class PatientsDao
{

public boolean login(String username,String password)
{
    Connection connection=JDBCKit.getConnection();
    PreparedStatement statement=null;
    ResultSet resultSet=null;
    try
    {
        statement=connection.prepareStatement("select *from patients where (account=? or name=?) and password=?");
        statement.setString(1, username);
        statement.setString(2, username);
        statement.setString(3, password);
        resultSet =statement.executeQuery();
        if(resultSet.next())
        {
            return true;
        }else {
            return false;
        }
    } catch (SQLException e)
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
        return false;
    }finally {
        JDBCKit.release(resultSet, statement, connection);
    }
}

}

调试发现conn 和stmt都为空，抛出异常
知道是select*语句出现了空指针但是不知道该怎么解决，困扰了好久了
补充下完整的报错：
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.Util.getInstance(Util.java:381)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:984)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:910)
at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3923)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1273)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2031)
at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:718)
at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:46)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
at cn.hh.DB.JDBCKit.getConnection(JDBCKit.java:35)
at cn.hh.Dao.PatientsDao.login(PatientsDao.java:16)
at cn.hh.servlet.LoginServlet.doPost(LoginServlet.java:37)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
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:52)
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:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:660)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:808)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
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:834)
5月 21, 2019 4:39:33 下午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [LoginServlet] in context with path [/Course] threw exception
java.lang.NullPointerException
at cn.hh.Dao.PatientsDao.login(PatientsDao.java:21)
at cn.hh.servlet.LoginServlet.doPost(LoginServlet.java:37)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
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:52)
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:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:660)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:808)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
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:834)

  • 写回答

4条回答 默认 最新

  • 毕小宝 博客专家认证 2019-05-21 09:21
    关注

    login 中打断点调试下，看看从哪一行开始空指针的。
    如果连接对象获取的时候就空了，再检查数据库连接配置信息。
    最后是查询语句的结果是否为空。

    评论

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