【设计模式】：Dao设计模式详解及一个简单的项目（AJAX+JSP+Servlet）

来源：互联网发布：centos 6.7 升级内核编辑：程序博客网时间：2024/05/17 08:45

迫于课程结束，老师逼着让做课程设计，就简单花了一天的时间写了个使用dao设计模式的东西~ ~ ~顺带在这里讲解下dao设计模式

把写个这个东西的源代码放上来：

http://download.csdn.net/detail/u010800530/8273915

先画一个图，这个图可能能够完整表达出dao设计模式的意思，但是可以在下边通过代码看出来：

一、完成登陆功能（未设计AJAX，等到完成显示列表的时候我们做AJAX）：

首先，我们建立一个项目TestJSP

然后，我们写一个login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>  </head>  <body>    <div  style="border: 1px solid #ccc;width:350;height:450;margin:auto auto;">    <br>        <center><h3>登陆界面</h3></center>       <br><br>       <br>      <form method="post" name="Login" action="login" onSubmit="return login();">       <table>       <tr>       <td>用户名：<input type="text" id="username" name="username"/></td>       </tr>       <tr>       <td>密  码：<input type="password" id="password" name="password" /></td>       </tr>       <br>       <tr>       <td><input type="submit" name="Submit" value="提交" /></td>       </tr>       </table>     </form>     </div>          <script type="text/javascript" >     function login()     {        var name = document.getElementById("username").value;     var pwd = document.getElementById("password").value;       if(name.length != 0 && pwd.length != 0){     return true;     }else{     alert("请输入姓名或者密码！");     return false;     }  }     </script>  </body></html>

多余的不用看，我们看表单提交选项，我们通过post方式提交表单到login

接下来，我们配置一下web.xml文件：

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <welcome-file-list>    <welcome-file>login.jsp</welcome-file>  </welcome-file-list><servlet>  <servlet-name>acceptLogin</servlet-name>  <servlet-class>com.cn.controller.LoginAction</servlet-class></servlet><servlet-mapping>  <servlet-name>acceptLogin</servlet-name>  <url-pattern>/login</url-pattern></servlet-mapping>      <servlet>  <servlet-name>listAction</servlet-name>  <servlet-class>com.cn.controller.ListAction</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>listAction</servlet-name>    <url-pattern>/list</url-pattern>  </servlet-mapping>    <servlet>  <servlet-name>deleteAction</servlet-name>  <servlet-class>com.cn.controller.DeleteAction</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>deleteAction</servlet-name>    <url-pattern>/deleteuser</url-pattern>  </servlet-mapping>  </web-app>

我们看第一个servlet，第一个servlet的路径是/login，刚好对应login.jsp中的路径。这个servlet指向com.cn.controller.LoginAction.java类，我们把这个servlet类写出来：

package com.cn.controller;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.cn.dao.UserDao;import com.cn.entity.User;import com.cn.factory.DAOFactory;public class LoginAction extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doPost(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {req.setCharacterEncoding("gb2312");User user = null;String username = req.getParameter("username").toString();  String password = req.getParameter("password").toString();    if(username == null || username.equals("")){  resp.sendRedirect("login.jsp");  }    if(password == null || password.equals("")){  resp.sendRedirect("login.jsp");  }    try {  UserDao dao = DAOFactory.getUserDAOInstance();   //标记1user = dao.queryByName(username);     //标记2if(user != null){System.out.println("user不为空");if((user.getPassword().trim()).equals(password.trim())){System.out.println("登陆成功");resp.sendRedirect("main.jsp");}else{System.out.println("密码错误");  resp.sendRedirect("login.jsp");}}else{System.out.println("登陆失败");  resp.sendRedirect("login.jsp");}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}  }}

我们看下doPost()方法中的try....catch代码块，这里边我写了两个标记。我们先看标记1。

1、标记1

我们先建立UserDao.java接口：

package com.cn.dao;import java.util.List;import com.cn.entity.User;public interface UserDao {public abstract boolean insert(User user) throws Exception;public abstract boolean deleteById(int userid) throws Exception;public abstract User queryByName(String name) throws Exception;public abstract User queryById(int userid) throws Exception;public abstract List<User> findAll() throws Exception;}

并且对这个接口进行实现UserDaoImpl.java：

package com.cn.dao.impl;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.util.ArrayList;import java.util.List;import com.cn.dao.DataBaseConnection;import com.cn.dao.UserDao;import com.cn.entity.User;public class UserDaoImpl implements UserDao {private Connection conn = null;private PreparedStatement pstmt = null;public UserDaoImpl(Connection conn) {this.conn = conn;}public boolean deleteById(int userid) throws Exception {String sql = "delete  from users where id="+userid;try{this.pstmt = this.conn.prepareStatement(sql);int row = this.pstmt.executeUpdate();if(row>0){this.pstmt.close();this.conn.close();System.out.println("Dao删除成功");return true;}else{this.pstmt.close();this.conn.close();System.out.println("Dao删除失败");return false;}}catch(Exception e){e.printStackTrace();this.pstmt.close();this.conn.close();return false;}}public List<User> findAll() throws Exception {List<User> userList = new ArrayList<User>();User user = null;String sql = "select * from users";try{this.pstmt = this.conn.prepareStatement(sql);ResultSet rs = this.pstmt.executeQuery();while(rs.next()){user = new User();user.setId(rs.getInt(1));user.setUsername(rs.getString(2));user.setPassword(rs.getString(3));System.out.println(user.getId()+" "+user.getUsername()+" "+user.getPassword());userList.add(user);}this.pstmt.close();this.conn.close();}catch (Exception e) {e.printStackTrace();}return userList;}public boolean insert(User user) throws Exception {// TODO Auto-generated method stubreturn false;}public User queryById(int userid) throws Exception {// TODO Auto-generated method stubreturn null;}public User queryByName(String name) throws Exception {User user = null;String sql = "select * from users where username=?";try{this.pstmt = this.conn.prepareStatement(sql);this.pstmt.setString(1,name);ResultSet rs = this.pstmt.executeQuery();if(rs.next()){user = new User();user.setId(rs.getInt(1));user.setUsername(rs.getString(2));user.setPassword(rs.getString(3));}this.pstmt.close();this.conn.close();}catch(Exception e){<pre name="code" class="java"><span style="white-space:pre"></span>e.printStackTrace();

}return user;}}

在这个类中，我们看下构造方法，这个构造方法传入了一个Connection类型参数，通过这个参数，我们在对这个类进行实例化的时候就会打开对数据库的链接。并通过这个链接执行sql语句。

2、标记2

user = dao.queryByName(username)

这句代码中的queryByName(username)方法调用的是UserDaoProxy.java代理类中的方法，这个代理类是对UserDao接口。我们写下UserDaoProxy.java:

package com.cn.daoProxy;import java.util.ArrayList;import java.util.List;import com.cn.dao.DataBaseConnection;import com.cn.dao.UserDao;import com.cn.dao.impl.UserDaoImpl;import com.cn.entity.User;public class UserDaoProxy implements UserDao {private DataBaseConnection dbc = null;private UserDao dao = null;public UserDaoProxy() {super();this.dbc = new DataBaseConnection();this.dao = new UserDaoImpl(this.dbc.getConnection());}public boolean deleteById(int userid) throws Exception {Boolean bo = this.dao.deleteById(userid);if(bo){return true;}else{return false;}}public List<User> findAll() throws Exception {List<User> userList = new ArrayList<User>();userList = this.dao.findAll();return userList;}public boolean insert(User user) throws Exception {return false;}public User queryById(int userid) throws Exception {// TODO Auto-generated method stubreturn null;}public User queryByName(String name) throws Exception {User user = null;try{user = this.dao.queryByName(name);}catch(Exception e){e.printStackTrace();}finally{dbc.close();}return user;}}

写到这里，我忘了把实体类的代码贴出来了：User.java

package com.cn.entity;public class User {private int id;private String username;private String password;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

然后，我们回到上边控制层的LoginAction.java，通过验证是否用户密码正确，判断可以登陆系统（这里没做拦截器）

二、完成列表显示（涉及到了AJAX）

当我们打开login.jsp，并输入用户名密码登陆之后，到了main.jsp页面，在这个页面我们要实现，打开这个页面的时候能够直接显示User表。

我们看下main.jsp页面：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>   <title>用户管理操作界面</title><script type="text/javascript" src="js/jquery-2.1.1.js"></script><script type="text/javascript" src="js/main.js"></script>  </head>    <body>  <h2 style="margin-left:44%; margin-top:9%;">用户管理操作界面</h2>  <form style="margin-left:42%;">  <input type="text" name="userid" style="width:60px;"><input type="submit" value="按Id查询" onclick="queryById()">  <input type="text" name="username" style="width:60px;"><input type="submit" value="按姓名查询" onclick="queryByName()"></form>   <table cellpadding="1" border="1" style="margin-left:43%; text-align: center;">   <tr>   <td>Id</td>   <td>姓名</td>   <td>密码</td>   <td>操作</td>   </tr>   </table>   <div id="myDiv"></div>  </body></html>

在这个页面，我们定义了一个table，并写了一个main.js，我们下边把main.js的代码贴上来：

//完成AJAX$(function(){var xmlhttp;   if(window.XMLHttpRequest){    xmlhttp=new XMLHttpRequest();   }else{    xmlhttp=new ActiveObject("Microsoft.XMLHTTP");   }   xmlhttp.onreadystatechange=function(){    if(xmlhttp.readyState==4 && xmlhttp.status==200){                  var data =xmlhttp.responseText; //接收到响应回来的text文本var datajson=eval("("+data+")"); //把String转换成json对象$.each(datajson.person,function(i,item){//对json对象进行解析//下边这些是把每条信息解析显示出来并添加到table中var $tr = $("<tr></tr>");var $td_1 = $("<td>"+item.id+"</td>");       var $td_2 = $("<td>"+item.username+"</td>");        var $td_3 = $("<td>"+item.password+"</td>");     var $td_4 = $("<input type='button' value='删除' onclick='deleteUser()' />" +      "<input type='button' value='更新' onclick='updateUser()'/>");    var $parent = $("table");                               $parent.append($tr);                 $tr.prepend($td_1);             $tr.append($td_2);    $tr.append($td_3);    $tr.append($td_4);});    }   };     xmlhttp.open("POST","list",true);   xmlhttp.send();});//删除方法function deleteUser(){if (!confirm("确认删除？")) {        window.event.returnValue = false;    }else{    var val = 1; //val是要删除的id，这里因为懒，直接把数据写死了    window.location.href="deleteuser?userid="+val;    }}//更新方法，懒没写function updateUser(){alert("update");}//通过id查询，懒没写function queryById(){}//通过name查询，懒没写function queryByName(){alert(2);}

通过AJAX，我们在页面刷新的时候提交一个请求，并且得到请求把相应的值用jquery添加到页面上边。

这是效果图，看起来是挺简单的：

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