程序突然就连不上数据库了，之前一直好好的，把登陆部分的代码贴上来，求大神给看看
jsp部分：<!DOCTYPE html>
<!--[if (gt IE 9)|!(IE)]><!--> <!--<![endif]-->
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="Login and Registration Form with HTML5 and CSS3" />
<meta name="keywords" content="html5, css3, form, switch, animation, :target, pseudo-class" />
<meta name="author" content="Codrops" />
<link rel="shortcut icon" href="../favicon.ico">
<link rel="stylesheet" type="text/css" href="css/demo.css" />
<link rel="stylesheet" type="text/css" href="css/style.css" />
<link rel="stylesheet" type="text/css" href="css/animate-custom.css" />
</head>
<body>
<div class="container">
<!-- Codrops top bar -->
<div class="codrops-top">
<div class="clr"></div>
</div><!--/ Codrops top bar -->
<header>
<nav class="codrops-demos">
</nav>
</header>
<section>
<div id="container_demo" >
<!-- hidden anchor to stop jump http://www.css3create.com/Astuce-Empecher-le-scroll-avec-l-utilisation-de-target#wrap4 -->
<a class="hiddenanchor" id="toregister"></a>
<a class="hiddenanchor" id="tologin"></a>
<div id="wrapper">
<div id="login" class="animate form">
<form action="com.xx.servlet/LoginServlet" method="post">
<h1>Log in</h1>
<p>
<label for="username" class="uname" data-icon="u" > Your username </label>
<input type="text" name="username" />
</p>
<p>
<label for="password" class="youpasswd" data-icon="p"> Your password </label>
<input type="password" name="password" />
</p>
<p class="keeplogin">
</p>
<p class="login button">
<input type="submit" value="Login" />
</p>
<p class="change_link">
Not a member yet ?
<a href="register.jsp" class="to_register">Join us</a>
</p>
</div>
</div>
</div>
</section>
</div>
</body>
servlet部分：package com.xx.servlet;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.spi.DirStateFactory.Result;
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 javax.servlet.http.HttpSession;
import com.bbs.*;
import com.mysql.jdbc.Driver;
/**
Servlet implementation class LoginServlet
*/
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
/**
/**
@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
request.setCharacterEncoding("utf-8");
String name = null;String level = null;
Connection conn = null;
Statement stmt=null;
ResultSet res=null;
boolean flag=false;//通过数据库匹配标识
String name_checked=null;//检查通过的用户名
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
String URL="jdbc:mysql://localhost:3306/mybbs";
String USER="root";
String PASSWORD="5438027";
//1.加载驱动程序
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e1) {
System.out.println("加载驱动失败1");// TODO 自动生成的 catch 块
e1.printStackTrace();
}
//2.获得数据库的链接
try {
DriverManager.registerDriver(new Driver());
conn=DriverManager.getConnection(URL, USER, PASSWORD);
} catch (SQLException e) {
System.out.println("加载失败2");// TODO 自动生成的 catch 块
e.printStackTrace();
}
String u=request.getParameter("username"); //从上级页面获得用户名
String p=request.getParameter("password"); //从上级页面获得密码
String sql="SELECT * FROM user WHERE userName IN('"+u+"') "+"AND passWord IN('"+p+"')";
System.out.println(sql);//执行上述sql语句
try {
res=stmt.executeQuery(sql);
} catch (SQLException e) {
System.out.println("加载失败3");// TODO 自动生成的 catch 块
e.printStackTrace();
}
try {
if(true==res.next())//只有查询得到结果才可进入循环
{
flag=true;
name_checked=res.getString("name");
level=res.getString("level");
}
} catch (SQLException e) {
System.out.println("加载失败4");// TODO 自动生成的 catch 块
e.printStackTrace();
}
if(true==flag)//登陆成功
{
HttpSession session=request.getSession();
session.setAttribute("userlevel",level);
session.setAttribute("name",name_checked);
response.sendRedirect(request.getContextPath()+"/loginsuccess.jsp");
User me=new User();
}
else//登陆失败
{
response.sendRedirect(request.getContextPath()+"/login.jsp");
}
}
}
报错：HTTP Status 500 -
type Exception report
message
description The server encountered an internal error that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
com.xx.servlet.LoginServlet.doPost(LoginServlet.java:99)
javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.82 logs.
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
conn=DriverManager.getConnection(URL, USER, PASSWORD);
这里的数据库服务器、用户名、密码你调试下，是不是变了
根据以往的经验首先判断数据库是否正常？先用工具进行登录，看账号密码的问题，如果成功，再断点看具体是哪句报错，一般很快就能找到问题所在
form表单没有结束标签， res=stmt.executeQuery(sql); 看你贴出来的代码stmt只声明了并没有创建sql命令发送器对象。
有个空指针，你看下LoginServlet的第99行，可能是没有new
没有 结束这个可能会影响你提交所以链接数据库失败！你细心点好好看一下form没有结束
conn.prepareStatement();
res=stmt.executeQuery(sql);
这样试一下，你的PreparedStatement为空，用Connection创建一下
exception已经提示很清楚了：java.lang.NullPointerException
程序有空指针，这个要自己逐行跟进去调试了
空指针异常，代码99行，你看一下有没有错的。用debug调试一下，看为什么后台收不到值
这么大的空指针，自己找一下哪空
空指针，需要标记出99行代码，才能根据上下文判断什么问题