关于MVC模式的简单解释
M Model，模型层，例如登录实例中，用于处理登录操作的类；
V View，视图层，用于展示以及与用户交互。使用html、js、css、jsp、jQuery等前端技术实现；
C Controller，控制器，接受视图层的请求，将请求跳转到对应的模型进行处理，模型层处理完毕后，再将结果返回给请求处。这里用Servlet实现控制器。
实现过程分析
用户再视图层输入用户名以及密码点击提交，向控制器发出请求
控制器（Servlet）接受请求，将接受到的用户名以及密码转给模型层
模型层依据用户名和密码在数据库中进行查询，将操作结果返回给控制器
控制器经过判断返回给用户登录结果。
代码实现
项目结构图
视图层实现(index.jsp)
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Login</title>
</head>
<body>
<form action="LoginServlet" method="post">
Name:<input type="text" name="uname"><br>
Pass:<input type="password" name="upwd"><br>
<input type="submit" value="Login"><br>
</form>
</body>
</html>
控制器层实现(LoginServlet)
package com.ajy.Servlet;
import com.ajy.Model.LoginDao;
import com.ajy.Entity.User;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
//控制器层
public class LoginServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理post方式登录请求
request.setCharacterEncoding("utf-8");
String uname = request.getParameter("uname");
String upwd = request.getParameter("upwd");
User user = new User(uname,upwd);
response.setContentType("text/html;charset=utf-8");
response.setCharacterEncoding("utf-8");
PrintWriter out = response.getWriter();
int rs = LoginDao.Login(user);
if(rs==-1){
out.println("系统错误");
}else if(rs==0){
out.println("用户名或密码错误");
}else{
out.println("登录成功");
}
}
}
模型层实现(LoginDao)
package com.ajy.Model;
import com.ajy.Entity.User;
import java.sql.*;
//模型层，用于处理登录操作
public class LoginDao {
private static String DBUname = "root";
private static String DBUpwd = "121181";
private static String URL="jdbc:mysql://localhost:3306/anjiyubase?&serverTimezone=UTC&useSSL=false";
public static int Login(User user){
Connection con = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
int count = 0;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
con = DriverManager.getConnection(URL,DBUname,DBUpwd);
pstmt = con.prepareStatement("select count(*) from users where uanme = ? and upwd = ?");
pstmt.setString(1,user.getUserName());
pstmt.setString(2,user.getUserPassword());
rs = pstmt.executeQuery();
if(rs.next()){
count = rs.getInt(1);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
return -1;
} catch (SQLException e) {
e.printStackTrace();
return -1;
}finally {
try {
if (rs!=null)rs.close();
if (pstmt!=null)pstmt.close();
if (con!=null)con.close();
} catch (SQLException e) {
e.printStackTrace();
return -1;
}
}
if (count==0){
return 0;
}else{
return 1;
}
}
}
用户实例(User)
package com.ajy.Entity;
public class User {
private int id;
private String UserName;
private String UserPassword;
public User(String UserName, String UserPassword){
this.UserName=UserName;
this.UserPassword=UserPassword;
}
public User(int id, String UserName, String UserPassword){
this.id=id;
this.UserName=UserName;
this.UserPassword=UserPassword;
}
public String getUserName() {
return UserName;
}
public void setUserName(String userName) {
UserName = userName;
}
public String getUserPassword() {
return UserPassword;
}
public void setUserPassword(String userPassword) {
UserPassword = userPassword;
}
}
web.xml中的内容
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<welcome-file-list>
<welcome-file>login.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.ajy.Servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/LoginServlet</url-pattern>
</servlet-mapping>
</web-app>
数据库
