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     <filter-mapping>
         <filter-name>struts2</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <welcome-file-list>
         <welcome-file>index.html</welcome-file>
     </welcome-file-list>

</web-app>清單1 WebContent/WEB-INF/web.xml
“#”主要有三種用途：

訪問OGNL上下文和Action上下文，#相當(dāng)于ActionContext.getContext()；下表有幾個ActionContext中有用的屬性：   名稱 作用 例子
parameters 包含當(dāng)前HTTP請求參數(shù)的Map #parameters.id[0]作用相當(dāng)于request.getParameter("id")
request 包含當(dāng)前HttpServletRequest的屬性（attribute)的Map #request.userName相當(dāng)于request.getAttribute("userName")
session 包含當(dāng)前HttpSession的屬性（attribute）的Map #session.userName相當(dāng)于session.getAttribute("userName")
application 包含當(dāng)前應(yīng)用的ServletContext的屬性（attribute）的Map #application.userName相當(dāng)于application.getAttribute("userName")
attr 用于按request > session > application順序訪問其屬性（attribute） #attr.userName相當(dāng)于按順序在以上三個范圍（scope）內(nèi)讀取userName屬性，直到找到為止

用于過濾和投影（projecting)集合，如books.{?#this.price<100}；
構(gòu)造Map，如#{'foo1':'bar1', 'foo2':'bar2'}。
下面讓我們它們的具體寫法，首先是Action類代碼：

package tutorial.action;

import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.apache.struts2.interceptor.ServletRequestAware;
import org.apache.struts2.interceptor.SessionAware;
import org.apache.struts2.util.ServletContextAware;

import tutorial.model.Book;

import com.opensymphony.xwork2.ActionSupport;

public class OgnlAction extends ActionSupport implements ServletRequestAware, SessionAware, ServletContextAware   {
     private static final long serialVersionUID = 1L;
    
     private HttpServletRequest request;
     private Map<String, String> session;
     private ServletContext application;
     private List<Book> books;
            
     public void setServletRequest(HttpServletRequest request) {
         this.request = request;    
     }

     @SuppressWarnings("unchecked")
     public void setSession(Map session) {
         this.session = session;        
     }

     public void setServletContext(ServletContext application) {
         this.application = application;
     }
    
     public List<Book> getBooks() {
         return books;
     }

     @Override
     public String execute() {
         request.setAttribute("userName", "Max From request");
         session.put("userName", "Max From session");
         application.setAttribute("userName", "Max From application");
        
         books = new LinkedList<Book>();
         books.add(new Book("978-0735619678", "Code Complete, Second Edition", 32.99));
         books.add(new Book("978-0596007867", "The Art of Project Management", 35.96));
         books.add(new Book("978-0201633610", "Design Patterns: Elements of Reusable Object-Oriented Software", 43.19));
         books.add(new Book("978-0596527341", "Information Architecture for the World Wide Web: Designing Large-Scale Web Sites", 25.19));
         books.add(new Book("978-0735605350", "Software Estimation: Demystifying the Black Art", 25.19));
        
         return SUCCESS;
     }
}清單2 src/tutorial/action/OgnlAction.java

以上代碼分別在request、session和application的范圍內(nèi)添加“userName”屬性，然后再在JSP頁面使用OGNL將其取回。我還創(chuàng)建了Book對象的列表用于演示“用于過濾和投影（projecting)集合”的功能，至于Book的代碼大家可以在我前一文章《在Struts 2中實現(xiàn)CRUD》看到。

下面是Ognl.jsp的代碼，內(nèi)容如下：

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>

最后是Struts 2的配置文件struts.xml，內(nèi)容如下：

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

發(fā)布運行應(yīng)用程序，結(jié)果如下所示：

清單5 示例運行結(jié)果1

“%”符號的用途是在標(biāo)志的屬性為字符串類型時，計算OGNL表達(dá)式的值。例如在Ognl.jsp中加入以下代碼：

<hr />
     <h3>%的用途</h3>
     <p><s:url value="#foobar['foo1']" /></p>
     <p><s:url value="%{#foobar['foo1']}" /></p>清單6 演示%用途的代碼片段
刷新頁面，結(jié)果如下所示：