java简单的MVC实现简单的用户注册与登录

本人对初次接触java ee，感觉这个简单的mvc实现的用户登录与注册比较的有参照价值。故记录下来。

本篇中的代码源自于《轻量级Java EE企业应用实战（第三版）》第二章，其原来的代码是实现用户登录，我在它的基础上依照它的写法添加了用户注册。代码很粗陋，但是能用。

Model模块代码，实现对数据库中表的操作

import java.sql.DriverManager;
import java.sql.ResultSet;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.PreparedStatement;

public class DbDao {
    private Connection conn;
    private String driver;
    private String url;
    private String username;
    private String pass;
    
    public DbDao(){
        
    }
    
    public DbDao(String driver, String url, String username, String pass) {
        this.driver = driver;
        this.url = url;
        this.username = username;
        this.pass = pass;
    }

    public Connection getConn() {
        return conn;
    }

    public void setConn(Connection conn) {
        this.conn = conn;
    }

    public String getDriver() {
        return driver;
    }

    public void setDriver(String driver) {
        this.driver = driver;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPass() {
        return pass;
    }

    public void setPass(String pass) {
        this.pass = pass;
    }
    
    // get database connection
    public Connection getConnection() throws Exception {
        if(conn == null){
            Class.forName(this.driver);
            conn = (Connection) DriverManager.getConnection(url, username, this.pass);
        }
        return conn;
    }
    
    // insert records
    public boolean insert(String sql, Object... args) throws Exception{
        PreparedStatement pstmt = (PreparedStatement) getConnection().prepareStatement(sql);
        for(int i = 0; i < args.length; i++) {
            pstmt.setObject(i + 1, args[i]); 
        }
        if(pstmt.executeUpdate() != 1)
            return false;
        return true;
    }
    
    // execute query
    public ResultSet query(String sql, Object...args) throws Exception{
        PreparedStatement pstmt = (PreparedStatement) getConnection().prepareStatement(sql);
        for(int i=0; i< args.length; i++) {
            pstmt.setObject(i+1, args[i]);
        }
        return pstmt.executeQuery();
    }
    
    public void modify(String sql, Object...args) throws Exception{
        PreparedStatement pstmt = (PreparedStatement)getConnection().prepareStatement(sql);
        for(int i = 0; i< args.length; i++) {
            pstmt.setObject(i+1, args[i]);
        }
        pstmt.executeUpdate();
        pstmt.close();
    }
    
    public void closeConn() throws Exception{
        if(conn != null && !conn.isClosed())
            conn.close();
    }
}

Control模块代码，用servlet实现请求的处理及对数据库的查询与修改。

import java.io.IOException;
import java.sql.ResultSet;

import javax.servlet.RequestDispatcher;
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;

@WebServlet(name="login", urlPatterns={"/login"})
public class LoginServlet extends HttpServlet{
    public void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String errMsg = "";
    RequestDispatcher rd;
    String username = request.getParameter("username");
    String pass = request.getParameter("pass");
    try {
        DbDao dd = new DbDao("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/test",
                "root", "root");
        
        // 查询结果集
        ResultSet rs = dd.query("select pass from user_table where username = ?", username);
        if(rs.next()){
            //用户名和密码匹配
            if(rs.getString("pass").equals(pass)) {
                //获取session对象
                HttpSession session = request.getSession(true);
                session.setAttribute("name", username);
                
                //获取转发对象
                rd = request.getRequestDispatcher("/welcome.jsp");
                
                // 转发请求
                rd.forward(request, response);
            } else {
                errMsg += "您的用户名密码不匹配，请重新输入";
            }
        } else {
            errMsg += "您的用户名不存在，请先注册";
        }
    }catch(Exception e) {
        e.printStackTrace();
    }
    // 如果出错，转发到重新登陆
    if(errMsg != null && !errMsg.equals("")){
        rd = request.getRequestDispatcher("/login.jsp");
        request.setAttribute("err", errMsg);
        rd.forward(request, response);
    }
    }
}

import java.io.IOException;
import java.sql.ResultSet;

import javax.servlet.RequestDispatcher;
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;

@WebServlet(name="register", urlPatterns={"/register"})
public class RegisterServlet extends HttpServlet{
    public void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String errMsg = "";
    RequestDispatcher rd;
    String username = request.getParameter("username");
    String pass = request.getParameter("pass");
    String conPass = request.getParameter("conPass");
    
    if((username.length()==0)|| (pass.length()==0)||!pass.equals(conPass))
        errMsg += "注册失败，请检查用户名和密码非空，并确定密码一致";

    else {
        try {
            DbDao dd = new DbDao("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/test",
                    "root", "root");
            ResultSet rs = dd.query("select pass from user_table where username = ?", username);
            if(rs.next()) {
                errMsg += "用户已经存在，请重新设置用户名";
            }
            else {
                boolean addUser = dd.insert("insert into user_table(username, pass) values(?, ?)",username, pass);
                if(!addUser) {
                    errMsg += "注册用户出现错误";
                }
                
                // 注册成功，转发到welcome.jsp
                HttpSession session = request.getSession(true);
                session.setAttribute("name", username);
                
                //获取转发对象
                rd = request.getRequestDispatcher("/welcome.jsp");
                
                // 转发请求
                rd.forward(request, response);
            }
            
        }catch(Exception e) {
            e.printStackTrace();
        }
    }
    // 如果出错，转发到重新注册
    if(errMsg != null && !errMsg.equals("")){
        rd = request.getRequestDispatcher("/register.jsp");
        request.setAttribute("err", errMsg);
        rd.forward(request, response);
    }
    }
}

View模块，用jsp呈现注册与登录页面，以及成功后的登录页面。

<%@ page language="java" contentType="text/html; charset=GBK"
    pageEncoding="UTF-8"%>
<!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</title>
</head>
<body>
<!-- 输出错误提示信息 -->
<span style="color:red; font-weight:bold">
<%
    if(request.getAttribute("err")!=null){
        out.println(request.getAttribute("err") + "<br/>");
    }
%>
</span>

请输入用户名和密码：
<form id="login" method="post" action="login">
    用户名：<input type="text" name="username" /><br/>
    密码&nbsp;<input type="password" name="pass" /><br/>
    <input type="submit" value="登陆"/><br/>
</form>
<a href="register.jsp">注册用户</a>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=GBK"
    pageEncoding="UTF-8"%>
<!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</title>
</head>
<body>
<!-- 输出错误提示信息 -->
<span style="color:red; font-weight:bold">
<%
    if(request.getAttribute("err")!=null){
        out.println(request.getAttribute("err") + "<br/>");
    }
%>
</span>

请输入用户名和密码：
<form id="login" method="post" action="register">
    用户名：<input type="text" name="username" /><br/>
    密码&nbsp;<input type="password" name="pass" /><br/>
    确认密码<input type="password" name="conPass" /><br/>
    <input type="submit" value="注册"/><br/>
</form>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=GBK"
    pageEncoding="UTF-8"%>
<!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>Welcome</title>
</head>
<body>
<h2>欢迎登陆, <%=request.getParameter("username") %></h2>
</body>
</html>

这里需要用到mysql数据库，在test数据库中建立user_table表，建表的语句可以如下（但不限于）

create table user_table(
id int primary key auto_increment,
username varchar(20),
pass varchar(20)
);