Question

这是我的JSP代码：

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<html>
<link rel="stylesheet" type="text/css" href="style/main.css">
<head>
<title>Trang chủ</title>
</head>
<body>
    <h2>Hello World ! I am phucpdbk :D</h2>
    <form style="width:400px; margin-left:auto;margin-right: auto;" method="POST" >
        <fieldset>
            <table cellpadding="10px" border="0">
                <tr>
                    <td>Username:</td>
                    <td><input class="inputText" type="text" name="username" /></td>
                </tr>
                <tr>
                    <td>Password:</td>
                    <td><input class="inputText" type="password" name="password" /></td>
                </tr>
                <tr>
                    <td><input type="reset" value="Reset" /></td>
                    <td><input type="submit" value="Submit" /></td>
                </tr>
            </table>
        </fieldset>
    </form>
    <%String message=(String) request.getAttribute("message"); %>
    <p> <%=message %></p>
</body>
</html>

这是servlet：

package com.login;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
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.*;

/**
 * Servlet implementation class Login
 */
public class Login extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Login() {
        super();
            // TODO Auto-generated constructor stub
    }

    /**
     * @see Servlet#init(ServletConfig)
     */
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
    }

    /**
     * @see HttpServlet#service(HttpServletRequest request, HttpServletResponse response)
     */
    protected void service(HttpServletRequest request, HttpServletResponse response)         throws ServletException, IOException {
        System.out.println("Login Serverlet ! :D ");
        String message="";
        //String userName="username";
        //String password="password";

        String requestUser=request.getParameter("username");
        String requestPass=request.getParameter("password");
        Connection connect = null;
        String url="jdbc:mysql://localhost:3306/";
        String dbname="logindb";
        String driver="com.mysql.jdbc.Driver";
        String userNameMySql="root";
        String passMySql="123123";
        String stringQuery="select * from login where user='"+ requestUser+"' and password='"+requestPass+"'";
        try {
            Class.forName(driver).newInstance();
            connect=DriverManager.getConnection(url+dbname,userNameMySql,passMySql);
            Statement statement=connect.createStatement();
            ResultSet resultSet = statement.executeQuery(stringQuery);
            if(resultSet.next()){
                message="Hello " + requestUser+".Login successful";
            }
            else{
                message="Hello " + requestUser+".Login failed";
            }
            resultSet.close();
            statement.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        request.setAttribute("message", message);
        RequestDispatcher reqDispatcher = getServletConfig().getServletContext().getRequestDispatcher("/MavenWebApp/index.jsp");
        reqDispatcher.forward(request,response);
    }

}

web.xml文件：

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>Login</servlet-name>
    <display-name>Login</display-name>
    <description>Login Serverlet</description>
    <servlet-class>com.login.Login</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Login</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

这是控制台中的异常显示：

Login Serverlet ! :D 
Nov 11, 2014 2:51:44 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Login] in context with path [/MavenWebApp]         threw exception
java.lang.NullPointerException
at com.login.Login.service(Login.java:79)
............................................

我已经在stackoverflow.com上进行过多次搜索，但它仍然无效。对不起，如果我的问题让你不舒服，因为我是初学者，我的英语不好：D

为什么我不能创建对JSP的Servlet响应？

0 个答案: