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" /> - $<s:property value="price" /></li> </s:iterator> </ul> <p>The price of "Code Complete, Second Edition" is: <s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/></p> <hr /> <h3>构造Map</h3> <s:set name="foobar" value="#{'foo1':'bar1', 'foo2':'bar2'}" /> <p>The value of key "foo1" is <s:property value="#foobar['foo1']" /></p> </body> </html>
以上代码值得注意的是“<s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/>”,因为“books.{?#this.title=='Code Complete, Second Edition'}.{price}”返回的值是集合类型,所以要用“[索引]”来访问其值。
发布运行应用程序,结果如下所示:
是在标志的属性为字符串类型时,计算OGNL表达式的值。例如在Ognl.jsp中加入以下代码:
<hr />
<h3>%的用途</h3>
<p><s:url value="#foobar['foo1']" /></p>
<p><s:url value="%{#foobar['foo1']}" /></p>
“$”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>