使用Servlet和jdbc创建用户登录验证

首先创建一个用户表，用来保存用户名 密码，并插入几条数据

mysql> desc user;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| username | varchar(20) | YES | | NULL | |
| password | varchar(50) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+

创建语句，注意一定要设置password的长度超过41，因为插入数据时我们使用password函数，生成长度为41的字符串，

例如：

mysql> select password('aasas');
+-------------------------------------------+
| password('aasas') |
+-------------------------------------------+
| *462034BF6D04324F93F1F6CA352B23079A165972 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql> select length( password('aasas'));
+----------------------------+
| length( password('aasas')) |
+----------------------------+
| 41 |
+----------------------------+
1 row in set (1.76 sec)

 CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(20) DEFAULT NULL,
`password` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 

插入数据：

mysql> insert into user(username,password) values('root',password('root'));

查看一下插入结果：此时密码已经变成一串字符串.

mysql> select * from user where username='root';
+----+----------+-------------------------------------------+
| id | username | password |
+----+----------+-------------------------------------------+
| 4 | root | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
+----+----------+-------------------------------------------+
1 row in set (0.00 sec)

2.创建一个java web project，新建一个名为user的类,使用jdbc链接数据库，把user表的数据拿出来和输入的用户名密码对比，并添加validate方法

如果用户名密码正确，返回true。之后注意将Mysql JDBC的driver copy到lib目录下，否则无法运行

package com.data;

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

public class user {

    private static String userName;
    private static String password;
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public static boolean validate()
    {
        String url = "jdbc:mysql://localhost:3306/study";
        String user= "root";
        String dbpassword = "3edc4rfv";
        boolean result = false;

        try {
             String driver ="com.mysql.jdbc.Driver";
             Class.forName(driver);
             Connection   con = DriverManager.getConnection(url,user, dbpassword);

            if(con==null){
                System.out.println("can't open DBConnection");
            }

            String sql = "select * from user where username=? and password=password(?)";

            PreparedStatement pstmt=con.prepareStatement(sql);
            pstmt.setString(1, userName);
            pstmt.setString(2, password);
            System.out.println(sql);
            ResultSet rs=pstmt.executeQuery();
            if(rs.next())
            {
                System.out.println("PASS");
                result=true;

            }
            else
            {
                System.out.println("FAIl");
                result=false;
            }
            pstmt.close();
            rs.close();
            con.close();

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return result;

    }

}

并新建一个Servlet，包名com.web，class name login.java，这里主要使用post方法，所以在dopost方法添加代码

将login.java 修改为这样：

package com.web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.data.book;
import com.data.user;

public class login extends HttpServlet {

    /**
     * Constructor of the object.
     */
    public login() {
        super();
    }

    /**
     * Destruction of the servlet. <br>
     */
    public void destroy() {
        super.destroy(); // Just puts "destroy" string in log
        // Put your code here
    }

    /**
     * The doGet method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to get.
     *
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

         //Add some codes
        doPost(request,response);
    }

    /**
     * The doPost method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to post.
     *
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
         request.getParameter("username");
         request.getParameter("password");
         request.getSession().setAttribute("user", request.getParameter("username"));      //将user放在Attribute中
         user user1=new user();
         user1.setUserName(request.getParameter("username"));
         user1.setPassword(request.getParameter("password"));
         System.out.println(request.getParameter("username")+request.getParameter("password"));

         if(user1.validate())
         {

             request.getRequestDispatcher("welcome.jsp").forward(request, response); //校验用户名密码正确，跳转到welcome.jsp

         }
         else
         {
             request.getRequestDispatcher("index.jsp").forward(request, response);  //校验用户名密码不正确，跳转到index.jsp

         }

    }
    /**
     * Initialization of the servlet. <br>
     *
     * @throws ServletException if an error occurs
     */
    public void init() throws ServletException {
        // Put your code here
    }

}

此时web.xml代码如下。可以使用login.do访问这个Servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <description>login Page</description>
    <display-name>login Page</display-name>
    <servlet-name>login</servlet-name>
    <servlet-class>com.web.login</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login.do</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

3.在jsp页面添加相应的action，在index.jsp的body标签之间添加，会生出登录界面，用户名 密码

 <form action="login.do" method="post" >
   username<input type="text" name="username">
   <br>password
   <input type="password" name="password">
   <br>
   <input type="submit"  value="login">
   <input type="reset" value="cancel"/>
   </form>

4.添加welcome.jsp

在welcome.jsp body标签添加

  Welcome <%=session.getAttribute("user") %><br>

5.加载工程