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)