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Java Web开发模式

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一 Java Web开发模式的变迁

1 最初的Java web服务器端编程技术是Servlet，利用Servlet就可以开发出一个Web应用程序。

2 为了解决Servlet缺陷，SUN推出了JSP技术。但是开发人员又走向了另一个极端就是完全放弃了Servlet。

在JSP页面混合使用HTML标记和java代码编写的脚本元素标记来开发Web程序。采用这种方法虽然可以编写JSP页面变得简单，直观，然而，他只适合于业务流程简单，系统规模较小的应用系统。

如果系统较大的话，就会出现两个严重的缺点：

1) 页面严重缺乏可读性。

2) 没有将页面表现和业务逻辑实现分开，使维护难度增加了。

在JSP中使用JavaBean可以实现页面与逻辑业务分开。

3 SUN公司将在Web应用开发中使用JSP+JavaBean技术。===JSP模式1 (适用于规模较小，业务逻辑简单的web应用开发)。

4 SUN在java web开发中引入了MVC架构模式，利用Servlet，JSP，JavaBean技术（讲servlet作为MVC架构模式中的控制器，JSP作为视图，javabean作为模型）===JSP模式2（）这也不是绝对完美的。

二在JSP中使用JavaBean

一个标准的JavaBean组件具有以下几个特征

 1 package com.cy.bean; 2  3 import java.io.Serializable; 4  5 /*JavaBean 类必须是一个公共类，并将其访问属性设置为 public。*/ 6 /*JavaBean应该是可序列化(serializable)的，即实现java.io.Serializable 接口  */ 7  8 public class User implements Serializable { 9 private static final long serialVersionUID = 1L;10 /* 一个JavaBean类不应有公共实例变量，类变量都为private */11 private int id;12 private String name;13 private String pwd;14 private int postion;15 16 /* JavaBean 类必须有一个空的构造函数，（系统会默认一个无参构造器，如果没有其他的构造器） */17 public User() {18 super();19 }20 21 /* 要访问这些类变量，应该通过一组存取方法（getXxx 和 setXxx）来访问， */22 public int getId() {23 retu id;24 }25 26 public void setId(int id) {27 this.id = id;28 }29 30 public String getName() {31 retu name;32 }33 34 public void setName(String name) {35 this.name = name;36 }37 38 public String getPwd() {39 retu pwd;40 }41 42 public void setPwd(String pwd) {43 this.pwd = pwd;44 }45 46 public int getPostion() {47 retu postion;48 }49 50 public void setPostion(int postion) {51 this.postion = postion;52 }53 54 }

为了在JSP页面中使用JavaBean，SUN在JSP规范中提供了三种标准动作。

1 <jsp:useBean>动作得到或者创建一个JavaBean对象

语法形式：

<jsp:useBean id=“beanName” //变量名 scope=“page|request|session|application” //作用范围 class=“className” //类全路径/>

1  <jsp:useBean id="user" class="com.cy.bean.User" scope="request"></jsp:useBean>

id:代表bean的引用名，id在一个页面中必须是一个唯一的值；User user = new User();

scope: 指定JavaBean生存的作用域

type:id的引用的数据类型，默认情况下，它与class的类型相同。

2 <jsp:getProperty>动作可以把JavaBean的某个属性取出来

语法形式：

<jsp:getProperty name="beanname" property="propertyname"/>

1 <jsp:getProperty property="name" name="user"/>

property: 指的是返回JavaBean中的相对应的属性名

3 <jsp:setProperty>动作设置JavaBean的属性值

其有四种语法形式：

<jsp:setProperty name="BeanName" property="属性名"/>

<jsp:setProperty name="BeanName" property="属性名" param="参数名"/>

<jsp:setProperty name="BeanName" property="属性名" value="属性值" />

<jsp:setProperty name="BeanName" property="*"/>

1 ----.jsp2 <jsp:setProperty property="name" name="user" param="useame"/>3<jsp:setProperty property="pwd" name="user" param="pwd"/>4 5 6 ----.html7  useame:<input type="text" name="useame"/>8pwd  :<input type ="password" name="pwd"/>

property:JavaBean相对应的属性

value设置属性的值

param将property指定的属性名的值设置为一个请求参数的值

property="*"用来设置所有与所得到的参数同名的属性值

三 JSP开发模式1

JSP模式1主要采用JSP和JavaBean技术

将页面显示与业务逻辑处理分开

JSP负责页面的显示，而业务逻辑则由JavaBean处理

用户登录案例来说明JSP1开发模式：

UserBean.java

 1 package com.cy.bean; 2  3 import java.io.Serializable; 4  5  6  7 public class UserBean implements Serializable { 8 private static final long serialVersionUID = 1L; 9 10 private String name;11 private String pwd;12 13 public UserBean () {14 super();15 }16 17 18 public String getName() {19 retu name;20 }21 22 public void setName(String name) {23 this.name = name;24 }25 26 public String getPwd() {27 retu pwd;28 }29 30 public void setPwd(String pwd) {31 this.pwd = pwd;32 }33 34 35 }

 1 <!DOCTYPE html> 2 <html> 3<head> 4 <title>login.html</title> 5  6 <meta name="keywords" content="keyword1,keyword2,keyword3"> 7 <meta name="description" content="this is my page"> 8 <meta name="content-type" content="text/html; charset=UTF-8"> 9 10 <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->11 12</head>1314<body>15<form action="/java_web/CheckUser.jsp" method="post">16useame:<input type="text" name="useame"/>17pwd  :<input type ="password" name="pwd"/>18<input type="submit" value="submit"/>19</form>20</body>21 </html>

CheckUserBean.java

 1 package com.cy.bean; 2  3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.ResultSet; 6 import java.sql.SQLException; 7 import java.sql.Statement; 8  9 public class CheckUserBean {10 11 public boolean checkUser(User user) {12 13 String name = user.getName();14 String pwd = user.getPwd();15 Connection conn = null;16 Statement st = null;17 ResultSet rs = null;18 String url = "jdbc:mysql://localhost:3306/demo";19 String user1 = "root";20 String password = "1234";21 String sql = "select * from t_user where user_name='" + name22 + "' and user_password='" + pwd + "'";23 try {24 Class.forName("com.mysql.jdbc.Driver");25 conn = DriverManager.getConnection(url, user1, password);26 st = conn.createStatement();27 rs = st.executeQuery(sql);28 29 if (rs.next()) {30 retu true;31 }32 } catch (Exception e) {33 e.printStackTrace();34 } finally {35 try {36 rs.close();37 st.close();38 conn.close();39 } catch (SQLException e) {40 e.printStackTrace();41 }42 }43 44 retu false;45 46 }47 }

CheckUser.jsp

 1 <%@ page language="java" import="java.util.*,com.cy.bean.*" pageEncoding="utf-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6  7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9<head>10 <base href="<%=basePath%>">11 12 <title>My JSP 'CheckUser.jsp' starting page</title>13 14 <meta http-equiv="pragma" content="no-cache">15 <meta http-equiv="cache-control" content="no-cache">16 <meta http-equiv="expires" content="0">17 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">18 <meta http-equiv="description" content="This is my page">19 <!--20 <link rel="stylesheet" type="text/css" href="styles.css">21 -->22 23</head>2425<body>26 <%CheckUserBean cub=new CheckUserBean(); %>27<jsp:useBean id="user" class="com.cy.bean.User" scope="request"></jsp:useBean>28<jsp:setProperty property="*" name="user"/>29<%if(cub.checkUser(user)) {%>30<jsp:forward page="success.jsp"></jsp:forward>31<%}else{%>32<jsp:forward page="fail.jsp"></jsp:forward>33<%} %>34</body>35 </html>

success.jsp

 1 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6  7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9<head>10 <base href="<%=basePath%>">11 12 <title>My JSP 'success.jsp' starting page</title>13 14 <meta http-equiv="pragma" content="no-cache">15 <meta http-equiv="cache-control" content="no-cache">16 <meta http-equiv="expires" content="0">17 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">18 <meta http-equiv="description" content="This is my page">19 <!--20 <link rel="stylesheet" type="text/css" href="styles.css">21 -->22 23</head>2425<body>26<jsp:useBean id="user" class="com.cy.bean.User" scope="request"></jsp:useBean> 2728欢迎你：<jsp:getProperty property="name" name="user"/>29</body>30 </html>

四 JSP开发模式2

JSP开发模式2借鉴了MVC架构模式，采用了Servlet+JSP+JavaBean的技术实现JavaWeb的开发。

1 MVC架构

在MVC中，模型（model）部分负责管理系统业务数据，视图（view）部分负责显示界面，控制器（controller）部分负责与用户的交互。

MVC示意图

2 MVC架构模式的Java Web实现

JSP开发模式2借鉴了MVC架构模式，采用了Servlet+JSP+JavaBean的技术实现JavaWeb的开发。

Servlet充当控制器额角色，负责处理请求和控制业务流程；

JSP充当视图的角色，负责输出响应结果；

JavaBean充当模型的角色，负责具体的业务逻辑和业务数据。

其结构如图：

WebMVC

3 JSP模式2开发步骤

–1 定义一系列Bean来表示数据

–2 使用一个Servlet来处理请求

–3 在Servlet中填充Bean

–4 在Servlet中，将Bean存储到请求、会话或者Servlet上下文中

–5 将请求转发到JSP页面

–6 在JSP页面中，从Bean中提取数据

1）

由于在MVC中，都是有Servlet或者其他的JAVA程序中创建Bean，所以我们开发的JavaBean也就不再需要有空构造器方法。

 1 package com.cy.bean; 2  3 import java.io.Serializable; 4  5 public class User implements Serializable { 6  7 private String name; 8 private String pwd; 9 10 public String getName() {11 retu name;12 }13 14 public void setName(String name) {15 this.name = name;16 }17 18 public String getPwd() {19 retu pwd;20 }21 22 public void setPwd(String pwd) {23 this.pwd = pwd;24 }25 26 }

–2 ) 使用一个Servlet来处理请求

–3 )在Servlet中填充Bean

–4 )在Servlet中，将Bean存储到请求、会话或者Servlet上下文中

–5 )将请求转发到JSP页面

 1 package com.cy.servlet; 2  3 import java.io.IOException; 4 import java.sql.Connection; 5 import java.sql.DriverManager; 6 import java.sql.ResultSet; 7 import java.sql.SQLException; 8 import java.sql.Statement; 9 10 import javax.servlet.ServletException;11 import javax.servlet.http.HttpServlet;12 import javax.servlet.http.HttpServletRequest;13 import javax.servlet.http.HttpServletResponse;14 15 import com.cy.bean.User;16 // 需要连接数据库17 public class LoginServlet extends HttpServlet{18 19 @Override20 protected void doGet(HttpServletRequest req, HttpServletResponse resp)21 throws ServletException, IOException {22 req.setCharacterEncoding("utf-8");23 resp.setCharacterEncoding("utf-8");24 resp.setContentType("text/html;charset=utf-8");25 26/*使用一个Servlet来处理请求*/27 String name = req.getParameter("useame");28 String pwd = req.getParameter("pwd");29 30 31 32 Connection conn = null;33 Statement st = null;34 ResultSet rs = null;35 String url="jdbc:mysql://localhost:3306/demo";36 String user = "root";37 String password  ="1234";38 String sql = "select * from t_user where user_name='"+name+"' and user_password='"+pwd+"'";39 40 //System.out.println(sql);41 try {42 Class.forName("com.mysql.jdbc.Driver");43 conn = DriverManager.getConnection(url,user,password);44 st = conn.createStatement();45 rs = st.executeQuery(sql);46 if(rs.next()){47 48/*在Servlet中填充Bean*/49 User u = new User();50 u.setPwd(pwd);51 u.setUseame(name);52 53 54 /*在Servlet中，将Bean存储到请求、会话或者Servlet上下文中*/55 req.getSession().setAttribute("user", u);56 57 /*将请求转发到JSP页面*/58 req.getRequestDispatcher("/welcome.jsp").forward(req, resp);59 }else{60 req.getRequestDispatcher("/index.jsp").forward(req, resp);61 }62 } catch (Exception e) {63 e.printStackTrace();64 }finally{65 try {66 rs.close();67 st.close();68 conn.close();69 } catch (SQLException e) {70 e.printStackTrace();71 }72 }73 74 }75 76 @Override77 protected void doPost(HttpServletRequest req, HttpServletResponse resp)78 throws ServletException, IOException {79 doGet(req, resp);80 }81 82 }

这里还写了一个简单的util

 1 package com.cy.util; 2  3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.ResultSet; 6 import java.sql.SQLException; 7 import java.sql.Statement; 8  9 public class DBUtil {10 private static String url = "jdbc:mysql://127.0.0.1:3306/demo?useUnicode=true&characterEncoding=utf-8"; 11 private static String user = "root";12 private static String pwd = "1234";13 private DBUtil(){};14 static{15 try {16 Class.forName("com.mysql.jdbc.Driver");17 } catch (ClassNotFoundException e) {18 e.printStackTrace();19 }20 21 }22 23 public static Connection getConn() throws SQLException{24 retu DriverManager.getConnection(url,user,pwd);25 }26 27 public static void closeRe(Connection conn,Statement st,ResultSet rs){28 if(rs!=null){29 try {30 rs.close();31 } catch (SQLException e) {32 e.printStackTrace();33 }finally{34 if(st!=null){35 try {36 st.close();37 } catch (SQLException e) {38 e.printStackTrace();39 }finally{40 if(conn!=null){41 try {42 conn.close();43 } catch (SQLException e) {44 e.printStackTrace();45 }46 }47 }48 }49 }50 }51 }52 53 public static void closeRe(Connection conn,Statement st) {54 if(st!=null){55 try {56 st.close();57 } catch (SQLException e) {58 e.printStackTrace();59 }finally{60 if(conn!=null){61 try {62 conn.close();63 } catch (SQLException e) {64 e.printStackTrace();65 }66 }67 }68 }69 70 }71 72 }

在web.xml配置Servlet

 1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  5 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 6 <display-name></display-name> 7 <welcome-file-list> 8 <welcome-file>index.jsp</welcome-file> 9 </welcome-file-list>10 11 <servlet>12 <servlet-name>login</servlet-name>13 <servlet-class>com.cy.servlet.LoginServlet</servlet-class>14 </servlet>15 16 <servlet-mapping>17 <servlet-name>login</servlet-name>18 <url-patte>/login</url-patte>19 </servlet-mapping>20 21 </web-app>

在JSP页面中，从Bean中提取数据

 1 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6  7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9<head>10 <base href="<%=basePath%>">11 12 <title>My JSP 'welcome.jsp' starting page</title>13 14 <meta http-equiv="pragma" content="no-cache">15 <meta http-equiv="cache-control" content="no-cache">16 <meta http-equiv="expires" content="0">17 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">18 <meta http-equiv="description" content="This is my page">19 <!--20 <link rel="stylesheet" type="text/css" href="styles.css">21 -->22 23</head>2425<body>26   welcome页码显示数据27<jsp:useBean id="user" type="com.cy.bean.User" scope="session"></jsp:useBean>28 <p>欢迎你：<jsp:getProperty property="name" name="user"></jsp:getProperty></p>29</body>30 </html>

五在MVC中使用过滤器

在创建Bean后，Servlet使用RequestDispatcher 对象将请求转发到恰当的JSP页面

Servlet

 1 package com.cy.servlet; 2  3 import java.io.IOException; 4  5 import javax.servlet.ServletException; 6 import javax.servlet.http.HttpServlet; 7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 10 import com.cy.bean.User;11 12 public class DemoServlet extends HttpServlet {13 14 @Override15 protected void doGet(HttpServletRequest req, HttpServletResponse resp)16 throws ServletException, IOException {17 req.setCharacterEncoding("utf-8");18 String name = req.getParameter("useame");19 String pwd = req.getParameter("pwd");20 21 User user = new User();22 user.setPwd(pwd);23 user.setUseame(name);24 req.getSession().setAttribute("user1", user);25 String uri = req.getRequestURI();26 req.getRequestDispatcher(uri).forward(req, resp);27 }28 29 @Override30 protected void doPost(HttpServletRequest req, HttpServletResponse resp)31 throws ServletException, IOException {32 doGet(req, resp);33 }34 35 }

Filter

 1 package com.cy.filter; 2  3 import java.io.IOException; 4  5 import javax.servlet.Filter; 6 import javax.servlet.FilterChain; 7 import javax.servlet.FilterConfig; 8 import javax.servlet.ServletException; 9 import javax.servlet.ServletRequest;10 import javax.servlet.ServletResponse;11 import javax.servlet.http.HttpServletRequest;12 13 import com.lovo.bean.User;14 15 public class DemoFilter implements Filter {16 17 public void destroy() {18 // TODO Auto-generated method stub19 20 }21 22 public void doFilter(ServletRequest arg0, ServletResponse arg1,23 FilterChain arg2) throws IOException, ServletException {24 HttpServletRequest req = (HttpServletRequest)arg0;25 User user = new User();26 String name = req.getParameter("useame");27 String pwd = req.getParameter("pwd");28 user.setPwd(pwd);29 user.setUseame(name);30 req.getSession().setAttribute("user", user);31 arg2.doFilter(req, arg1);32 }33 34 public void init(FilterConfig arg0) throws ServletException {35 // TODO Auto-generated method stub36 37 }38 39 }

在web.xml中配置部署Filter，servlet

 1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  5 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 6 <display-name></display-name> 7 <welcome-file-list> 8 <welcome-file>index.jsp</welcome-file> 9 </welcome-file-list>10 11 <filter>12 <filter-name>jsp</filter-name>13 <filter-class>com.cy.filter.DemoFilter</filter-class>14 </filter>15 <filter-mapping>16 <filter-name>jsp</filter-name>17 <url-patte>/*</url-patte>18 </filter-mapping>19 30 31 </web-app>