Servlet、JSP和JavaBean实现MVC实战

布满荆棘的人生 2021-07-25 01:13 371阅读 0赞

**一 视图——充当View**

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title> 用户登录 </title>
        <meta name="website" content="http://www.crazyit.org" />
    </head>
    <body>
    
    <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 &nbsp码：<input type="password" name="pass"/><br/>
    <input type="submit" value="登录"/><br/>
    </form>
    </body>
    </html>

welcome.jsp

**二 控制器——充当Controller**

package lee;
    
    import javax.servlet.*;
    import javax.servlet.http.*;
    import javax.servlet.annotation.*;
    
    import java.io.PrintWriter;
    import java.io.IOException;
    
    import java.sql.*;
    
    
    @WebServlet(name="login"
        , urlPatterns={"/login"})
    public class LoginServlet extends HttpServlet
    {
        // 响应客户端请求的方法
        public void service(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException,java.io.IOException
        {
            String errMsg = "";
            // Servlet本身并不输出响应到客户端，因此必须将请求转发到视图页面
            RequestDispatcher rd;
            // 获取请求参数
            String username = request.getParameter("username");
            String pass = request.getParameter("pass");
            try
            {
                // Servlet本身并不执行任何的业务逻辑处理，它调用JavaBean处理用户请求
                DbDao dd = new DbDao("com.mysql.jdbc.Driver",
                    "jdbc:mysql://localhost:3306/liuyan","root","123456");
                // 查询结果集
                ResultSet rs = dd.query("select pass from user_inf"
                    + " where name = ?", 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);
                        // 设置session属性，跟踪用户会话状态
                        session.setAttribute("name" , username);
                        // 获取转发对象
                        rd = request.getRequestDispatcher("/welcome.jsp");
                        // 转发请求
                        rd.forward(request,response);
                    }
                    else
                    {
                        // 用户名和密码不匹配时
                        errMsg += "您的用户名密码不符合,请重新输入";
                    }
                }
                else
                {
                    // 用户名不存在时
                    errMsg += "您的用户名不存在,请先注册";
                }
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
            // 如果出错，转发到重新登录
            if (errMsg != null && !errMsg.equals(""))
            {
                rd = request.getRequestDispatcher("/login.jsp");
                request.setAttribute("err" , errMsg);
                rd.forward(request,response);
            }
        }
    }

**三 JavaBean——充当Model**

package lee;
    
    import java.sql.*;
    
    
    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;
        }
        // 下面是各个成员属性的setter和getter方法
        public void setDriver(String driver) {
            this.driver = driver;
        }
        public void setUrl(String url) {
            this.url = url;
        }
        public void setUsername(String username) {
            this.username = username;
        }
        public void setPass(String pass) {
            this.pass = pass;
        }
        public String getDriver() {
            return (this.driver);
        }
        public String getUrl() {
            return (this.url);
        }
        public String getUsername() {
            return (this.username);
        }
        public String getPass() {
            return (this.pass);
        }
        // 获取数据库连接
        public Connection getConnection() throws Exception
        {
            if (conn == null)
            {
                Class.forName(this.driver);
                conn = DriverManager.getConnection(url,username,
                    this. pass);
            }
            return conn;
        }
        // 插入记录
        public boolean insert(String sql , Object... args)
            throws Exception
        {
            PreparedStatement pstmt = getConnection().prepareStatement(sql);
            for (int i = 0; i < args.length ; i++ )
            {
                pstmt.setObject( i + 1 , args[i]);
            }
            if (pstmt.executeUpdate() != 1)
            {
                return false;
            }
            pstmt.close();
            return true;
        }
        // 执行查询
        public ResultSet query(String sql , Object... args)
            throws Exception
        {
            PreparedStatement pstmt = getConnection().prepareStatement(sql);
            for (int i = 0; i < args.length ; i++ )
            {
                pstmt.setObject( i + 1 , args[i]);
            }
            return pstmt.executeQuery();
        }
        // 执行修改
        public void modify(String sql , Object... args)
            throws Exception
        {
            PreparedStatement pstmt = getConnection().prepareStatement(sql);
            for (int i = 0; i < args.length ; i++ )
            {
                pstmt.setObject( i + 1 , args[i]);
            }
            pstmt.executeUpdate();
            pstmt.close();
        }
        // 关闭数据库连接的方法
        public void closeConn()
            throws Exception
        {
            if (conn != null && !conn.isClosed())
            {
                conn.close();
            }
        }
    }

**四 数据库**

drop database if exists liuyan;
    create database liuyan;
    
    use liuyan;
    
    create table user_inf
    (
        id int auto_increment primary key,
        name varchar(255),
        pass varchar(255)
    );
    
    insert into user_inf
    values(null,'crazyit','123');
    insert into user_inf
    values(null,'tiger','123');

**五 测试**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/df423f1ad2b44f849786d28292f70757.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 1]: /images/20210724/d31ea35f361d48a3a69d36b6faa1c630.png