【数据库创建脚本】

USE weitang;
DROP TABLE IF EXISTS user ;
CREATE TABLE user(
    userid      VARCHAR(30)     PRIMARY KEY ,
    name        VARCHAR(30)     NOT NULL ,
    password        VARCHAR(32)     NOT NULL
) ;
INSERT INTO user (userid,name,password) VALUES ('admin','kyle','12345') ;

【User.java】定义VO类

package im.weitang.vo;

public class User {
    private String userid;
    private String name;
    private String password;

    public String getUserid() {
        return userid;
    }

    public void setUserid(String userid) {
        this.userid = userid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

【DatabaseConnection.java】定义数据库操作类

package im.weitang.dbc;

import java.sql.Connection;
import java.sql.DriverManager;

public class DatabaseConnection {
    private static final String DBDRIVER = "org.gjt.mm.mysql.Driver";
    private static final String DBURL = "jdbc:mysql://localhost:3306/weitang";
    private static final String DBUSER = "root";
    private static final String UDPASSWORD = "123456";
    private Connection conn = null;

    public DatabaseConnection() throws Exception {
        try {
            Class.forName(DBDRIVER);
            this.conn = DriverManager.getConnection(DBURL, DBUSER, UDPASSWORD);
        } catch (Exception e) {
            throw e;
        }
    }

    public Connection getConnection() {
        return this.conn;
    }

    public void close() throws Exception {
        if (this.conn != null) {
            try {
                this.conn.close();
            } catch (Exception e) {
                throw e;
            }
        }
    }
}

【IUserDAO.java】定义DAO接口

package im.weitang.dao;

import im.weitang.vo.User;

public interface IUserDAO {
    
    /**
     * 用户登录验证
     * @param user 传入VO对象
     * @return 验证的操作结果
     * @throws Exception
     */
    public boolean findLogin(User user) throws Exception;
}

【UserDAOImpl.java】定义DAO实现类

package im.weitang.dao.impl;

import im.weitang.dao.IUserDAO;
import im.weitang.vo.User;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class UserDAOImpl implements IUserDAO {

    private Connection conn = null;
    private PreparedStatement pstmt = null;

    public UserDAOImpl(Connection conn) {
        this.conn = conn;
    }

    @Override
    public boolean findLogin(User user) throws Exception {
        boolean flag = false;

        try {
            String sql = "SELECT name FROM user WHERE userid=? AND password=?";
            this.pstmt = this.conn.prepareStatement(sql);
            this.pstmt.setString(1, user.getUserid());
            this.pstmt.setString(2, user.getPassword());
            ResultSet rs = this.pstmt.executeQuery();

            if (rs.next()) {
                user.setName(rs.getString(1));
                flag = true;
            }
        } catch (Exception e) {
            throw e;
        } finally {
            if (this.pstmt != null) {
                try {
                    this.pstmt.close();
                } catch (Exception e) {
                    throw e;
                }
            }
        }
        return flag;
    }
}

【UserDAOProxy.java】定义DAO代理操作类

package im.weitang.dao.proxy;

import im.weitang.dao.IUserDAO;
import im.weitang.dao.impl.UserDAOImpl;
import im.weitang.dbc.DatabaseConnection;
import im.weitang.vo.User;

public class UserDAOProxy implements IUserDAO {
    private DatabaseConnection dbc = null;
    private IUserDAO dao = null;

    public UserDAOProxy() {
        try {
            this.dbc = new DatabaseConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        this.dao = new UserDAOImpl(this.dbc.getConnection());
    }

    @Override
    public boolean findLogin(User user) throws Exception {
        boolean flag = false;

        try {
            flag = this.dao.findLogin(user);
        } catch (Exception e) {
            throw e;
        } finally {
            this.dbc.close();
        }

        return flag;
    }

}

【DAOFactory.java】定义工厂类

package im.weitang.factory;

import im.weitang.dao.IUserDAO;
import im.weitang.dao.proxy.UserDAOProxy;

public class DAOFactory {
    public static IUserDAO getIUserDAOInstance() {
        return new UserDAOProxy();
    }
}

【LoginServlet.java】

package im.weitang.servlet;

import im.weitang.factory.DAOFactory;
import im.weitang.vo.User;

import java.io.IOException;
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;

public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String path = "login.jsp";
        String userid = request.getParameter("userid");
        String userpass = request.getParameter("userpass");

        List<String> info = new ArrayList<String>();

        if (userid == null || "".equals(userid)) {
            info.add("用户id不能为空！");
        }
        if (userpass == null || "".equals(userpass)) {
            info.add("密码不能为空");
        }
        if (info.size() == 0) {
            User user = new User();
            user.setUserid(userid);
            user.setPassword(userpass);

            try {
                if (DAOFactory.getIUserDAOInstance().findLogin(user)) {
                    info.add("用户登录成功，欢迎" + user.getName() + "光临！");
                } else {
                    info.add("用户登录失败，用户名或密码错误！");
                }
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        request.setAttribute("info", info);
        request.getRequestDispatcher(path).forward(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

最后修改web.xml，添加如下代码：

<servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>im.weitang.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
</servlet-mapping>

【login.jsp】

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import="java.util.*"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>标题</title>
</head>
<body>

    <script>
        function validate(f) {
            if (!(/^\w{5,15}$/.test(f.userid.value))) {
                alert("用户ID必须是5~15位！");
                f.userid.focus();
                return false;
            }
            if (!(/^\w{5,15}$/.test(f.userpass.value))) {
                alert("密码必须是5~15位！");
                f.userpass.focus();
                return false;
            }
        }
    </script>
    <%
        request.setCharacterEncoding("UTF-8");
    %>
    <%
        List<String> info = (List<String>) request.getAttribute("info");
        if (info != null) { // 有信息返回
            Iterator<String> iter = info.iterator();
            while (iter.hasNext()) {
    %>
    <h4><%=iter.next()%></h4>
    <%
        }
        }
    %>
    <form action="LoginServlet" method="post"
        onSubmit="return validate(this)">
        用户ID：<input type="text" name="userid"><br>
        密  码：<input type="password" name="userpass"><br>
        <input type="submit" value="登陆"> <input type="reset"
            value="重置">
    </form>

</body>
</html>