Eclipse新建web项目，实现登录验证功能

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安装好MySQl数据库

这里写图片描述

新建JavaWeb项目

项目名称为test3

文件层次

    在Web-Content目录下新建login.jsp文件       在浏览器中，需要提交的东西，使用表单form标签来进行提交，form中的action的值是表单数据提交到的jsp或Servlet的地址

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"    pageEncoding="ISO-8859-1"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Login Page</title> </head><body><form action="LoginServlet">                                    //此处的LoginServlet为相对位置username:<input type ="text" name="username"/><br>password:<input type = "password" name="password"/><br><input type ="submit" name ="submit"/></form></body></html>

新建名为MySQL的类来进行数据库操作

package com.lx.uestc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;public class MySQL {    private Connection connection = null;public  MySQL(){    /*加载JdBC驱动     *      */    try {        Class.forName("com.mysql.jdbc.Driver");        System.out.println("load Driver successfully");    } catch (Exception e) {        System.out.println("load  Driver error");        e.printStackTrace();    }    /*连接数据库     *      */    try {       connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","liangxi333");        //jdbc:mysql://localhost:端口号/数据库名称","用户名","密码"        System.out.println("connect sql successfully");    } catch (Exception e) {        System.out.println("connect sql erro");        e.printStackTrace();    }    /*检查用户账号密码正否     *      */}/*连接数据库后要记得关闭 *  */private void CloseSqlConnect(Connection connection ){    if (connection != null)        try{            connection.close();        }catch (Exception e) {            e.printStackTrace();        }}private ResultSet execSQL(String sql,Object... args) throws SQLException{    //建立PreparedStatement对象    PreparedStatement pStmt = connection.prepareStatement(sql);    //为pStmt对象设置SQL参数值    for(int i = 0; i < args.length; i++){        pStmt.setObject(i+1, args[i]);    }    //执行SQL语句    pStmt.execute();    //返回结果集,如果执行的SQL语句不返回结果集，则返回null    return pStmt.getResultSet();}public String checkUser(String username,String password){    boolean has_username = false;    boolean password_correct = false;    ResultSet rs = null;    try {        rs = execSQL("select * from user");    } catch (SQLException e) {        System.err.println("查询数据库出错");        e.printStackTrace();        return null;    }    try {        while(rs.next()){            String temp_username = rs.getString("name").trim();            String temp_password = rs.getString("password").trim();            if(username.equals(temp_username)){                has_username = true;                if(password.equals(temp_password)){                    password_correct = true;                    return "hasUserNameAndPasswordCorrect";                }                return "hasUserNameButPasswordInCorrect";            }        }    } catch (SQLException e) {        System.err.println("操作ResultSet出错");        e.printStackTrace();    }    return "hasNoUserName";}}

新建LoginServlet来响应浏览器请求

import java.io.IOException;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 java.io.OutputStream;import java.io.PrintWriter;public class LoginServlet extends HttpServlet {    private static final long serialVersionUID = 1L;    public LoginServlet() {        super();    }    public  void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.setContentType("text/html");         String username = request.getParameter("username");         String password = request.getParameter("password");         PrintWriter  output = response.getWriter();         output.println("<html><head><title> hello</title></head>");         MySQL mss = new MySQL();      //实例化数据库对象        String result = mss.checkUser(username,password);    if (result.equals("hasUserNameAndPasswordCorrect")) {    output.println("<body>user and password correct</body></html>");          System.out.println("用户名和密码均正确");    } else if (result.equals("hasUserNameButPasswordInCorrect")) {    output.println("<body>user correct but password wrong</body></html>");        System.out.println("用户名正确,密码不正确");        } else if (result.equals("hasNoUserName")) {        output.println("<body>no user</body></html>");            System.out.println("没有此用户");    }    output.flush();    }    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        doGet(request, response);    }}

测试工程

  今天在测试中遇到一个问题，浪费很多时间,在测试的过程中，发现MySQL在实例化的过程中出错，原因是找不到 com.mysql.jdbc.Driver ，但是我确实是导入到工程中的。 最后发现原因：tomcat在加载JDBC驱动时，Class.forName("com.mysql.jdbc.Driver");不会在项目的lib目录下寻找，而是在Tomcat—>lib目录下寻找，解决方法就是直接拷贝mysql-connector-java-5.0.8.jar到该目录下就可以 最后附上测试结果

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