OGNL中的#,%,$
OGNL的用法
OGNL是通常要结合Struts 2的标志一起使用，如<s:property value="xx" />等。大家经常遇到的问题是#、%和$这三个符号的使用。下面我想通过例子讲述这个问题：
“#”主要有三种用途：
1. 访问OGNL上下文和Action上下文，#相当于ActionContext.getContext()；下表有几个ActionContext中有用的属性：
| 名称 |
作用 |
例子 |
| parameters |
包含当前HTTP请求参数的Map |
#parameters.id[0]作用相当于request.getParameter("id") |
| request |
包含当前HttpServletRequest的属性（attribute)的Map |
#request.userName相当于request.getAttribute("userName") |
| session |
包含当前HttpSession的属性（attribute）的Map |
#session.userName相当于session.getAttribute("userName") |
| application |
包含当前应用的ServletContext的属性（attribute）的Map |
#application.userName相当于application.getAttribute("userName") |
| attr |
用于按request > session > application顺序访问其属性（attribute） |
#attr.userName相当于按顺序在以上三个范围（scope）内读取userName属性，直到找到为止 |
2. 用于过滤和投影（projecting)集合，如books.{?#this.price<100}；
3.构造Map，如#{'foo1':'bar1', 'foo2':'bar2'}。
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;
}
}
以上代码分别在request、session和application的范围内添加“userName”属性，然后再在JSP页面使用OGNL将其取回。我还创建了Book对象的列表用于演示“用于过滤和投影（projecting)集合”的功能。
下面是Ognl.jsp的代码，内容如下：
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!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>Struts OGNL Demo</title>
</head>
<body>
<h3>访问OGNL上下文和Action上下文</h3>
<p>parameters: <s:property value="#parameters.userName" /></p>
<p>request.userName: <s:property value="#request.userName" /></p>
<p>session.userName: <s:property value="#session.userName" /></p>
<p>application.userName: <s:property value="#application.userName" /></p>
<p>attr.userName: <s:property value="#attr.userName" /></p>
<hr />
<h3>用于过滤和投影（projecting)集合</h3>
<p>Books more than $35</p>
<ul>
<s:iterator value="books.{?#this.price > 35}">
<li><s:property value="title" /> - $<s:property value="price" /></li>
</s:iterator>
</ul>
<p>The price of "Code Complete, Second Edition" is: <s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/></p>
<hr />
<h3>构造Map</h3>
<s:set name="foobar" value="#{'foo1':'bar1', 'foo2':'bar2'}" />
<p>The value of key "foo1" is <s:property value="#foobar['foo1']" /></p>
</body>
</html>
以上代码值得注意的是“<s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/>”，因为“books.{?#this.title=='Code Complete, Second Edition'}.{price}”返回的值是集合类型，所以要用“[索引]”来访问其值。
发布运行应用程序，结果如下所示：
“%”符号的用途
是在标志的属性为字符串类型时，计算OGNL表达式的值。例如在Ognl.jsp中加入以下代码：
<hr />
<h3>%的用途</h3>
<p><s:url value="#foobar['foo1']" /></p>
<p><s:url value="%{#foobar['foo1']}" /></p>
刷新页面，结果如下所示：
“$”有两个主要的用途
1. 用于在国际化资源文件中，引用OGNL表达式
2. 在Struts 2配置文件中，引用OGNL表达式，如
<action name="AddPhoto" class="addPhoto">
<interceptor-ref name="fileUploadStack" />
<result type="redirect">ListPhotos.action?albumId=${albumId}</result>
</action>