struts2基础——需要注意的几点

struts是流行和成熟的基于MVC设计模式的web应用程序框架，使用struts可以帮助我们减少运用MVC设计模型来开发web应用的时间。

一、struts2的工作原理及文件结构

二、三种访问Servlet API的方式

三、struts接收参数的三种方式

四、自定义拦截器

一、struts2的工作原理及文件结构

注：FilterDispatcher被替成StrutsPrepareAndExecuteFilter（如果使用FilterDispatcher过滤器时，程序员自己写的Filter过滤器必须放在所有过滤器的前面。而StrutsPrepareAndExecuteFilter过滤器可以让程序员在执行action之前写自己的Filter）

描述Struts流程：

网页产生HttpServletRequest请求->经过多个过滤器->到达ActionMaaper，判断是否是action请求（如果是）->通过StrutsPrepareAndExecuteFilter过滤器到达Actionproxy，一方面通过configuration Manager（配置管理器）读取struts.xml文档，另一方面创建一个实例，经过一系列的拦截器->执行到Action->返回result(对应了视图)->经过一系列的拦截器（逆序）->通过HttpServletResponse返回到用户实例。

二、三种访问servlet API的方法

struts2中没有提供任何一个servlet对象，不存在HttpServletRequest，HttpServletResponse对象。但是Struts2提供了三种方式间接的去访问Servlet API

1、ActionContext

通过ActionContext的getContext()静态方法获取ActionContext对象，通过ActionContext对象的一些getSession(),getApplication(),put()等方法，但是千万要注意的是，get获取到的对象都为Map键值对类型。com.opensymphony.xwork2.ActionContext

 public String execute() {

         if ("ping".equals(username)) {

             /*

              * ActionContext可以获得Servlet对象 但是无法获得response响应对象获得

              * 获得的request、session、Application 都是Map类型

              */

             ActionContext.getContext().put("用户名", username);

             Map session=ActionContext.getContext().getSession();

             Map application=ActionContext.getContext().getApplication();

             Map request=(Map)ActionContext.getContext().get(StrutsStatics.HTTP_REQUEST);

         } else {

             ActionContext.getContext().put("info", "信息");

         }

         return SUCCESS;

     }

2、ServletActionContext

通过调用ServletActionContext类的一些包括getResponse(),getRequest(),getServletContext()等在内的静态方法，这些静态方法的返回类型是和Servlet中的对象类型是一一对应的。其中getResponse()返回类型为HttpServletResponse，getRequest()返回类型为HttpServletRequest().

 public String execute2() throws IOException {

         if ("ping".equals(username)) {

             HttpServletResponse response=ServletActionContext.getResponse();

 4             HttpServletRequest request=ServletActionContext.getRequest();

             HttpSession session=ServletActionContext.getRequest().getSession();

             ServletContext application=ServletActionContext.getServletContext();

         } else {

         }

         System.out.println(username);

         return SUCCESS;

     }

3、实现xxxAware接口

（1）实现ServletRequestAware，ServletResponseAware，ServletSessionAware

 public class LoginAction extends ActionSupport implements ServletRequestAware

 private HttpServletRequest request;

 //需实现方法 public void setServletRequest(HttpServletRequest request) { this.request=request; } //response示例

 public String execute1() throws IOException {

         if ("ping".equals(username)) {

             response.setContentType("text/html;charset=utf-8");

             PrintWriter out = response.getWriter();

             out.print("<script type='text/javascript'>alert('验证码输入错误!')</script>");

             out.print("<script type='text/javascript'>location.href='/index.jsp'</script>");

             out.flush();

             out.close();

         } else {

             response.setContentType("text/html;charset=utf-8");

             PrintWriter out = response.getWriter();

             out.print("<script type='text/javascript'>alert('验证码输入错误!')</script>");

             out.flush();

             out.close();

         }

         System.out.println(username);

         return SUCCESS;

     }

（2）实现RequestWare、SessionWare、ApplicationWare等接口

public class LoginAction2 extends ActionSupport implements RequestAware,SessionAware, ApplicationAware {

    private Map<String, Object> request;

    private Map<String, Object> session;

    private Map<String, Object> application;

    //DI dependency injection

    //IoC inverse of control

    public String execute() {

        request.put("r1", "r1");

        session.put("s1", "s1");

        application.put("a1", "a1");

        return SUCCESS;

    }

    @Override

    public void setRequest(Map<String, Object> request) {

        this.request = request;

    }

    @Override

    public void setSession(Map<String, Object> session) {

        this.session = session;

    }

    @Override

    public void setApplication(Map<String, Object> application) {

        this.application = application;

    }

}

三、struts三种接收参数方式

Struts有三种方式接收参数，且这三种方式都是自动完成赋值的setter方法。

1、使用Action的属性接收参数

代码：

struts.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE struts PUBLIC

      "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"

      "http://struts.apache.org/dtds/struts-2.3.dtd">

<struts>

<package name="default" namespace="/" extends="struts-default">

  <action name="LoginAction" method="login" class="com.third.LoginAction1">

    <result>/loginSuccess.jsp</result>

  </action>

</package>

</struts>

<%@ page language="java" contentType="text/html; charset=UTF-8"

    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=UTF-8">

<title>Insert title here</title>

</head>

<body>

<h1>login page</h1>

    <form action="LoginAction.action" method="post">

       <table>

          <tr>

             <td>username:</td>

             <td><input type="text" name="username"/></td>

          </tr>

           <tr>

             <td>password:</td>

             <td><input type="password" name="password"/></td>

          </tr>

          <tr>

             <td><input type="submit" value="submit"></td>

             <td><input type="reset" value="reset"></td>

          </tr>

       </table>

    </form>

</body>

</html>

loginSuccess.jsp（登陆成功提示界面）

<%@ page language="java" contentType="text/html; charset=UTF-8"

    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=UTF-8">

<title>login success!</title>

</head>

<body>

<h1>login success!</h1>

</body>

</html>

LoginAction.java

 package com.third;

 import com.opensymphony.xwork2.ActionSupport;

 public class LoginAction1 extends ActionSupport {

     private String username;

     private String password;

     public String login(){
        //这里能够打印出来传入的值，则说明能够自动调用setter方法完成赋值

         System.out.println("username:"+username+"  password:"+password);

         return SUCCESS;

     }

     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;

     }

 }

运行结果截图：

2、使用DomainModel接收参数

注：这里在表单传值是，必须指明这个属性值，到底穿个action中的那个引用，例如user.username.

代码：

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">

<struts>

   <package name="default" namespace="/" extends="struts-default">

      <action name="LoginAction" method="login" class="com.third.LoginAction">

        <result>/loginSuccess.jsp</result>

      </action>

   </package>

</struts>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'login.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

  <h1>login page!</h1>

   <form action="LoginAction.action" method="post">

       <table>

          <tr>

             <td>username:</td>

             <td><input type="text" name="user.username"/></td>

          </tr>

           <tr>

             <td>password:</td>

             <td><input type="password" name="user.password"/></td>

          </tr>

          <tr>

             <td><input type="submit" value="submit"></td>

             <td><input type="reset" value="reset"></td>

          </tr>

       </table>

    </form>

  </body>

</html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'loginSuccess.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

      <h1>login success!</h1>

  </body>

</html>

User.java

package com.third;

public class User {

    private String username;

    private String password;

    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;

    }

}

LoginAction.java

 package com.third;

 import org.apache.struts2.ServletActionContext;

 import com.opensymphony.xwork2.ActionContext;

 import com.opensymphony.xwork2.ActionSupport;

 import com.opensymphony.xwork2.inject.Context;

 public class LoginAction extends ActionSupport {

     private User user;

     public User getUser() {

         return user;

     }

     public void setUser(User user) {

         this.user = user;

     }

     public String login(){
          //这里可以打印出传入的值的话，Action完成了自动调用setter方法赋值

         System.out.println("username:"+user.getUsername()+" password:"+this.getUser().getPassword());

         return SUCCESS;

     }

 }

运行结果截图：

3、使用ModelDriven接受参数

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">

<struts>

   <package name="default" namespace="/" extends="struts-default">

      <action name="LoginAction" method="login" class="com.third.LoginAction">

        <result>/loginSuccess.jsp</result>

      </action>

   </package>

</struts>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'login.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

  <h1>login page!</h1>

   <form action="LoginAction.action" method="post">

       <table>

          <tr>

             <td>username:</td>

             <td><input type="text" name="username"/></td>

          </tr>

           <tr>

             <td>password:</td>

             <td><input type="password" name="password"/></td>

          </tr>

          <tr>

             <td><input type="submit" value="submit"></td>

             <td><input type="reset" value="reset"></td>

          </tr>

       </table>

    </form>

  </body>

</html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'loginSuccess.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

      <h1>login success!</h1>

  </body>

</html>

User.java

package com.third;

public class User {

    private String username;

    private String password;

    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;

    }

}

LoginAction.java

package com.third;

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionContext;

import com.opensymphony.xwork2.ActionSupport;

import com.opensymphony.xwork2.ModelDriven;

import com.opensymphony.xwork2.inject.Context;

public class LoginAction extends ActionSupport implements ModelDriven<User> {

    private User user=new User();

    public String login(){
      //这里打印出传入的参数值，说明自动调用setter方法赋值

        System.out.println("username:"+user.getUsername()+" password:"+user.getPassword());

        return SUCCESS;

    }

    @Override

    public User getModel() {

        return user;

    }

}

运行结果截图：

四、自定义拦截器

注：特别要注意在使用拦截的器的时候，使用表单传值，会导致Action中获得的属性的值为null，或是其他的默认的初始化值。

1、实现Interceptor接口

-void init()方法：初始化拦截器所需要的资源

-void destory()方法：释放init()中分配的资源

-String intercept(ActionInvocation invocation)throws Exception:实现拦截器功能，利用ActionInvocation参数获取Action状态，返回result字符串作为逻辑视图。

代码：

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">

<struts>

   <package name="default" namespace="/" extends="struts-default">

   <!--注册拦截器  -->

      <interceptors>

         <interceptor name="timefigureFilter" class="com.third.TimeInterceptor">

         </interceptor>

      </interceptors>

      <action name="LoginAction" method="login" class="com.third.LoginAction">

        <result>/loginSuccess.jsp</result>

        <interceptor-ref name="timefigureFilter"></interceptor-ref>

      </action>

   </package>

</struts>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'login.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

  <h1>login page!</h1>

   <form action="LoginAction.action" method="post">

       <table>

          <tr>

             <td>username:</td>

             <td><input type="text" name="username"/></td>

          </tr>

           <tr>

             <td>password:</td>

             <td><input type="password" name="password"/></td>

          </tr>

          <tr>

             <td><input type="submit" value="submit"></td>

             <td><input type="reset" value="reset"></td>

          </tr>

       </table>

    </form>

  </body>

</html>

loginSuccess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'loginSuccess.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

      <h1>login success!</h1>

  </body>

</html>

User.java

package com.third;

public class User {

    private String username;

    private String password;

    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;

    }

}

TimeInterceptor.java

 package com.third;

 import javax.servlet.http.HttpServletRequest;

 import org.apache.struts2.ServletActionContext;

 import com.opensymphony.xwork2.ActionInvocation;

 import com.opensymphony.xwork2.interceptor.Interceptor;

 public class TimeInterceptor implements Interceptor {

     @Override

     public void destroy() {

         // TODO Auto-generated method stub

     }

     @Override

     public void init() {

         // TODO Auto-generated method stub

     }

     @Override

     public String intercept(ActionInvocation invocation) throws Exception {

         HttpServletRequest request=ServletActionContext.getRequest();

         String username=request.getParameter("username");

         String password=request.getParameter("password");

         request.setAttribute("username", username);

         //1执行action之前

         long start=System.currentTimeMillis();

         //2执行下一个拦截器，直到最后一个拦截器，则执行目标Action

         String result=invocation.invoke();

         //3执行完action之后

         long end=System.currentTimeMillis();

         System.out.println("执行Action花费的时间为："+(end-start)+"ms");

         return result;

     }

 }

LoginAction.java

 package com.third;

 import org.apache.struts2.ServletActionContext;

 import com.opensymphony.xwork2.ActionContext;

 import com.opensymphony.xwork2.ActionSupport;

 import com.opensymphony.xwork2.ModelDriven;

 import com.opensymphony.xwork2.inject.Context;

 public class LoginAction extends ActionSupport implements ModelDriven<User> {

     private User user=new User();

     public String login(){
           //着重看着两行代码运行打印的结果

         System.out.println("username:"+user.getUsername());
           //System.out.println("username:"+ServletContext.getRequest().getAttribute("username");//这里也可完成正常的获值

         System.out.println("username:"+ServletActionContext.getRequest().getAttribute("username"));

         return SUCCESS;

     }

     @Override

     public User getModel() {

         return user;

     }

 }

运行结果截图：

注：注意看结果，打印的第一个username的属性值为null，而第二个为表单填写的dasd。这里涉及到拦截器的使用导致的表单传值问题。

分析：拦截器的使用导致的表单传值问题

原因：登陆界面填写完成之后，表单需要实现页面跳转，而这些将会交给struts，struts在调用action的过程其实是调用action中的struts.xml配置action标签method属性指定的方法（默认是execute()）,而在调用这个方法前会对表单的属性信息将会别匹配赋值给action中同名属性。正常情况下没有自定义的拦截器，通过表单传递的属性值没有问题。

要完成这个功能，有很大程度上， Struts 2 要依赖与 ValueStack 对象。这个对象贯穿整个 Action 的生命周期 (每个 Action 类的对象实例会拥有一个 ValueStack 对象 ) 。当 Struts 2 接收到一个 action 的请求后，会先建立Action 类的对象实例，但不会调用 Action 方法，而是先将 Action 类的相应属性放到 ValueStack 对象的顶层节点(ValueStack 对象相当于一个栈 ). 只是所有的属性值都是默认的值，如 String 类型的属性值为 null,int 类型的属性值为 0 等。

在处理完上述工作后， Struts 2 就会调用拦截器链中的拦截器，当调用完所有的拦截器后，最后会调用 Action 类的 Action 方法，在调用 Action 方法之前，会将 ValueStack 对象顶层节点中的属性值赋给 Action 类中相应的属性。大家要注意，在这里就给我们带来了很大的灵活性。也就是说，在 Struts 2 调用拦截器的过程中，可以改变ValueStack 对象中属性的值，当改变某个属性值后， Action 类的相应属性值就会变成在拦截器中最后改变该属性的这个值。

好多废话~总结就是：在拥有自定义的过滤器时，表单传属性值会先赋值给Action中属性，当运行完过滤器时，才会调用Action中的方法，在调用之前会将 ValueStack 对象中的默认初始化值赋给action中的属性，然后调用action中的方法，这样action中的属性全是ValueStack 对象中的默认初始化值。

解决的方法：间接访问Servlet的API，通过request对象去访问属性和属性值。如：

HttpServletRequest request=ServletActionContext.getRequest();

String username=request.getParameter("username");

2、方式二：继承AbstractInterceptor类

-提供了init()和destroy()方法的实现

-只需要实现intercept()方法即可

代码：

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">

<struts>

   <package name="default" namespace="/" extends="struts-default">

   <!--注册拦截器  -->

      <interceptors>

          <interceptor name="timefigureFilter1" class="com.third1.TimeInterceptor">

         </interceptor>

      </interceptors>

       <action name="TimeAction" class="com.third1.TimeAction">

        <result>/index.jsp</result>

        <!--引用拦截器  -->

        <interceptor-ref name="timefigureFilter1"></interceptor-ref>

      </action>

   </package>

</struts>

TimeInterceptor.java

 package com.third1;

 import org.apache.struts2.ServletActionContext;

 import com.opensymphony.xwork2.ActionInvocation;

 import com.opensymphony.xwork2.interceptor.AbstractInterceptor;

 public class TimeInterceptor extends AbstractInterceptor {

     @Override

     public String intercept(ActionInvocation invocation) throws Exception {

         //1.执行action之前

         long start=System.currentTimeMillis();

         //2.执行下一个拦截器，如果已经是最后一个拦截器，则执行目标Action

         ServletActionContext.getRequest().setAttribute("username", "小帅哥");

         ServletActionContext.getRequest().getSession().setAttribute("username","小美女");

         ServletActionContext.getServletContext().setAttribute("username", "少艾");

         String result=invocation.invoke();

         //3.执行Action之后

         long end=System.currentTimeMillis();

         System.out.println("执行Action花费的时间："+(end-start)+"ms");

         //获取request对象，调用其setAttribute函数，将时间作为属性保存到request对象中

         ServletActionContext.getRequest().setAttribute("time", (end-start));

         ServletActionContext.getRequest().getSession().setAttribute("time1",(end-start));

         ServletActionContext.getServletContext().setAttribute("time2", (end-start));

         return result;

     }

 }

TimeAction.java

 package com.third1;

 import com.opensymphony.xwork2.ActionSupport;

 public class TimeAction extends ActionSupport {

     @Override

     public String execute() throws Exception{

         for(int i=0;i<3;i++){

             Thread.sleep(1000);

         }

         return SUCCESS;

     }

 }

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'index.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

   <h1>执行Action用户名：<%=request.getAttribute("username") %>（通过request方式获取）</h1>

   <h1>执行Action用户名：<%=session.getAttribute("username") %>（通过session方式获取）</h1>

   <h1>执行Action用户名：<%=application.getAttribute("username") %>（通过application方式获取）</h1>

   <h1>执行Action花费的时间：<%=request.getAttribute("time") %>（通过request方式获取）</h1>

   <h1>执行Action花费的时间：<%=session.getAttribute("time1") %>（通过session方式获取）</h1>

   <h1>执行Action花费的时间：<%=application.getAttribute("time2") %>（通过application方式获取）</h1>

  </body>

</html>

运行结果截图：

分析：对比两种颜色标记的代码区，对比一下他们，并且结合结果进行分析。我们不难发现过滤器的调用分为两个阶段，第一个阶段是在产生HttpServletRequest请求之后、action方法调用之前；第二阶段是产生与action之后，jsp页面（Template显示）跳转之后，HttpServletResponse之前。所以当你在 String result=invocation.invoke(); 这条语句之后通过request，application，session给它设置属性值，将会没有起到任何作用。

可以结合struts2的工作原理及文件结构图进行参考。