Servlet实现用户的登录功能

首先，前面我们已经实现与数据库的连接和用户的注册功能，接下来就是用户通过已经注册的信息进行登录功能的实现

1.接前两篇博客，首先先编写一个简单的登录页面，代码如下：

 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 7 <title>用户登录页面</title>
 8 </head>
 9 <body>
10      <h2>${remind}</h2>
11      <h1>登录页面</h1>
12      
13      <form action="login" method="post">
14            登录名:<input type="text" name="name"><br/>
15              密码为:<input type="password" name="password"><br/>
16            <input type="submit" value="登录">
17      </form>
18      
19      <h5>还未注册，快来注册</h5>
20      <a href="register">注册</a>
21 </body>
22 </html>

2.编写实现用户登录的Servlet,在此处新建一个Servlet,命名为LoginServlet.java ，同时在web.xml配置文件中实现对该Servlet的配置，在web.xml的配置如下所示：

代码如下：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
 3   <display-name>Test1</display-name>
 4   <welcome-file-list>
 5     <welcome-file>index.html</welcome-file>
 6     <welcome-file>index.htm</welcome-file>
 7     <welcome-file>index.jsp</welcome-file>
 8     <welcome-file>default.html</welcome-file>
 9     <welcome-file>default.htm</welcome-file>
10     <welcome-file>default.jsp</welcome-file>
11   </welcome-file-list>
12   <servlet>
13     <servlet-name>RegisterServlet</servlet-name>
14     <servlet-class>lin.Servlet.RegisterServlet</servlet-class>
15   </servlet>
16   <servlet-mapping>
17     <servlet-name>RegisterServlet</servlet-name>
18     <url-pattern>/register</url-pattern>
19   </servlet-mapping>
20   <servlet>
21      <servlet-name>LoginServlet</servlet-name>
22      <servlet-class>lin.Servlet.LoginServlet</servlet-class>
23   </servlet>
24   <servlet-mapping>
25      <servlet-name>LoginServlet</servlet-name>
26      <url-pattern>/login</url-pattern>
27   </servlet-mapping>
28 </web-app>

3.编写LoginServlet.java的代码，代码如下：

 1 package lin.Servlet;
 2 
 3 import java.io.IOException;
 4 import java.sql.Connection;
 5 import java.sql.PreparedStatement;
 6 import java.sql.ResultSet;
 7 import java.sql.SQLException;
 8 
 9 import javax.servlet.ServletException;
10 import javax.servlet.annotation.WebServlet;
11 import javax.servlet.http.HttpServlet;
12 import javax.servlet.http.HttpServletRequest;
13 import javax.servlet.http.HttpServletResponse;
14 
15 import lin.db.DBServlet;
16 import lin.entity.User;
17 
18 /**
19  * Servlet implementation class LoginServlet
20  */
21 /*@WebServlet("/LoginServlet")*/
22 public class LoginServlet extends HttpServlet {
23     private static final long serialVersionUID = 1L;
24        
25     /**
26      * @see HttpServlet#HttpServlet()
27      */
28     public LoginServlet() {
29         super();
30         // TODO Auto-generated constructor stub
31     }
32 
33     /**
34      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
35      */
36     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
37         // TODO Auto-generated method stub
38         request.getRequestDispatcher("/WEB-INF/page/login.jsp").forward(request, response);
39     }
40 
41     /**
42      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
43      */
44     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
45         // TODO Auto-generated method stub
46         //设置utf-8，防止出现乱码情况
47         request.setCharacterEncoding("UTF-8");
48         response.setCharacterEncoding("text/html;charset=UTF-8");
49         
50         
51         //获取实体User中的变量，将变量插入到数据库中，完成注册
52          User user=new User();
53          //获取注册的用户名,"name"要与jsp页面中的变量名一致
54          String name=request.getParameter("name");
55          //获取注册的密码
56          String password=request.getParameter("password");
57         
58          
59          try {
60          //sql 语句用于查询name和password是否与数据库中存储的一致
61          String sql="select * from t_users where name=? and password=?;";
62          DBServlet db=new DBServlet();
63          //与数据库获得连接
64          Connection conn=db.getConn();
65          
66          //SQL语句被预编译并存储在PreparedStatement对象中
67         PreparedStatement statement=conn.prepareStatement(sql);
68         //将sql语句的问号值添加进去
69         statement.setString(1, name);
70         statement.setString(2, password);
71         
72         //执行sql语句
73         ResultSet rs=statement.executeQuery();
74         if(rs.next())
75         {
76             System.out.println("登录成功，欢迎你："+name);
77             request.setAttribute("remind", "登录成功");
78             request.getRequestDispatcher("/WEB-INF/page/login.jsp").forward(request, response);
79         }else
80         {
81             System.out.println("登录失败，密码或用户名错误");
82             request.setAttribute("remind", "登录成功");
83             request.getRequestDispatcher("/WEB-INF/page/login.jsp").forward(request, response);
84         }
85         
86         //关闭数据库
87         rs.close();
88         statement.close();
89         conn.close();
90         
91         } catch (SQLException e) {
92             // TODO Auto-generated catch block
93             System.out.println("数据库连接失败");
94             e.printStackTrace();
95         }
96     
97     }
98 
99 }

4.测试：先注册一个用户，例如，用户名：易烊千玺1 密码：123456

点击登录，之后

控制台输出如下所示：

这里对用户的登录功能的实现已经成功，拜拜了，，，，，，

还不知道接下来要写什么，好好学习了，对于servlet的理解应该也差不多了，试着写写前端和框架吧