OGNL表达式的用法

Dear 丶 2022-07-16 14:49 237阅读 0赞

<table style="width: 100%; table-layout: fixed;"> 
 <tbody> 
 <tr> 
 <td> 
 <div> 
 OGNL的用法 
 OGNL是通常要结合Struts 2的标志一起使用，如&lt;s:property value="xx" /&gt;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： 
 首先新建名为Struts2_OGNL的Web工程，配置开发环境。之前很多朋友在使用Struts 2的过程中都遇到乱码问题。当然乱码问题由来已久，而且涉及多方面的知识，所以并非三言两语可以说明白，而且互联网上也已经有很多这方便的文章，大家可以Google一下。不过，如果你在开发的过程，多注意一下，避免乱码问题也不难。乱码多数是由于编码与解码所使用的方式不同造成的，所以我建议大家将编码方式都设为“utf-8”，如&lt;%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %&gt;。另外，在配置web.xml时使用ActionContextCleanUp过滤器（Filter），如下面代码所示： 
 清单1 WebContent/WEB-INF/web.xml 
 &lt;?xml version="1.0" encoding="UTF-8"?&gt; &lt;web-app id="WebApp_9" version="2.4" &nbsp;&nbsp;&nbsp; xmlns="<a href="http://java.sun.com/xml/ns/j2ee" rel="nofollow">http://java.sun.com/xml/ns/j2ee</a>" &nbsp;&nbsp;&nbsp; xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" rel="nofollow">http://www.w3.org/2001/XMLSchema-instance</a>" &nbsp;&nbsp;&nbsp; xsi:schemaLocation="<a href="http://java.sun.com/xml/ns/j2ee" rel="nofollow">http://java.sun.com/xml/ns/j2ee</a> <a href="http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" rel="nofollow">http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd</a>"&gt; 
 &nbsp;&nbsp;&nbsp; &lt;display-name&gt;Struts 2 OGNL&lt;/display-name&gt; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &lt;filter&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-name&gt;struts-cleanup&lt;/filter-name&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-class&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; org.apache.struts2.dispatcher.ActionContextCleanUp &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/filter-class&gt; &nbsp;&nbsp;&nbsp; &lt;/filter&gt; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &lt;filter-mapping&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-name&gt;struts-cleanup&lt;/filter-name&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;url-pattern&gt;/*&lt;/url-pattern&gt; &nbsp;&nbsp;&nbsp; &lt;/filter-mapping&gt; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &lt;filter&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-name&gt;struts2&lt;/filter-name&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-class&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; org.apache.struts2.dispatcher.FilterDispatcher &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/filter-class&gt; &nbsp;&nbsp;&nbsp; &lt;/filter&gt; 
 &nbsp;&nbsp;&nbsp; &lt;filter-mapping&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;filter-name&gt;struts2&lt;/filter-name&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;url-pattern&gt;/*&lt;/url-pattern&gt; &nbsp;&nbsp;&nbsp; &lt;/filter-mapping&gt; 
 &nbsp;&nbsp;&nbsp; &lt;welcome-file-list&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;welcome-file&gt;index.html&lt;/welcome-file&gt; &nbsp;&nbsp;&nbsp; &lt;/welcome-file-list&gt; 
 &lt;/web-app&gt; 
 “#”主要有三种用途： 
 <p style="text-align: left; line-height: 150%; text-indent: -18pt; background: white; margin-left: 36pt; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l4 level1 lfo4;">1.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 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： 
 
 <table style="margin-left: 36pt; mso-padding-alt: 1.5pt 1.5pt 1.5pt 1.5pt; mso-cellspacing: 0cm;"> 
 <tbody> 
 <tr style="height: 14.25pt; mso-yfti-irow: 0; mso-yfti-firstrow: yes;"> 
 <td style="border-bottom: green 1pt solid; border-left: medium none; background: #ccffcc; height: 14.25pt; border-top: medium none; border-right: medium none; mso-border-bottom-alt: solid green .75pt; padding: 1.5pt;"> 名称 </td> 
 <td style="border-bottom: green 1pt solid; border-left: medium none; background: #ccffcc; height: 14.25pt; border-top: medium none; border-right: medium none; mso-border-bottom-alt: solid green .75pt; padding: 1.5pt;"> 作用 </td> 
 <td style="border-bottom: green 1pt solid; border-left: medium none; background: #ccffcc; height: 14.25pt; border-top: medium none; border-right: medium none; mso-border-bottom-alt: solid green .75pt; padding: 1.5pt;"> 例子 </td> 
 </tr> 
 <tr style="mso-yfti-irow: 1;"> 
 <td style="padding: 1.5pt;"> parameters </td> 
 <td style="padding: 1.5pt;"> 包含当前HTTP请求参数的Map </td> 
 <td style="padding: 1.5pt;"> #parameters.id[0]作用相当于request.getParameter("id") </td> 
 </tr> 
 <tr style="mso-yfti-irow: 2;"> 
 <td style="padding: 1.5pt;"> request </td> 
 <td style="padding: 1.5pt;"> 包含当前HttpServletRequest的属性（attribute)的Map </td> 
 <td style="padding: 1.5pt;"> #request.userName相当于request.getAttribute("userName") </td> 
 </tr> 
 <tr style="mso-yfti-irow: 3;"> 
 <td style="padding: 1.5pt;"> session </td> 
 <td style="padding: 1.5pt;"> 包含当前HttpSession的属性（attribute）的Map </td> 
 <td style="padding: 1.5pt;"> #session.userName相当于session.getAttribute("userName") </td> 
 </tr> 
 <tr style="mso-yfti-irow: 4;"> 
 <td style="padding: 1.5pt;"> application </td> 
 <td style="padding: 1.5pt;"> 包含当前应用的ServletContext的属性（attribute）的Map </td> 
 <td style="padding: 1.5pt;"> #application.userName相当于application.getAttribute("userName") </td> 
 </tr> 
 <tr style="mso-yfti-irow: 5; mso-yfti-lastrow: yes;"> 
 <td style="padding: 1.5pt;"> attr </td> 
 <td style="padding: 1.5pt;"> 用于按request &gt; session &gt; application顺序访问其属性（attribute） </td> 
 <td style="padding: 1.5pt;"> #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 </td> 
 </tr> 
 </tbody> 
 </table> 
 
 <p style="text-align: left; line-height: 150%; text-indent: -18pt; background: white; margin-left: 36pt; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l4 level1 lfo4;">2.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 用于过滤和投影（projecting)集合，如books.{?#this.price&lt;100}； 
 <p style="text-align: left; line-height: 150%; text-indent: -18pt; background: white; margin-left: 36pt; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-list: l4 level1 lfo4;">3.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 构造Map，如#{'foo1':'bar1', 'foo2':'bar2'}。 
 下面让我们它们的具体写法，首先是Action类代码： 
 清单2 src/tutorial/action/OgnlAction.java 
 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&nbsp;&nbsp; { &nbsp;&nbsp; private static final long serialVersionUID = 1L; &nbsp;&nbsp; &nbsp;&nbsp; private HttpServletRequest request; &nbsp;&nbsp; private Map&lt;String, String&gt; session; &nbsp;&nbsp; private ServletContext application; &nbsp;&nbsp; private List&lt;Book&gt; books; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; public void setServletRequest(HttpServletRequest request) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.request = request;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; } 
 &nbsp;&nbsp; @SuppressWarnings("unchecked") &nbsp;&nbsp; public void setSession(Map session) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.session = session;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; } 
 &nbsp;&nbsp; public void setServletContext(ServletContext application) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.application = application; &nbsp;&nbsp; } &nbsp;&nbsp; &nbsp;&nbsp; public List&lt;Book&gt; getBooks() { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return books; &nbsp;&nbsp; } 
 &nbsp;&nbsp; @Override &nbsp;&nbsp; public String execute() { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; request.setAttribute("userName", "Max From request"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; session.put("userName", "Max From session"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; application.setAttribute("userName", "Max From application"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books = new LinkedList&lt;Book&gt;(); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books.add(new Book("978-0735619678", "Code Complete, Second Edition", 32.99)); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books.add(new Book("978-0596007867", "The Art of Project Management", 35.96)); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books.add(new Book("978-0201633610", "Design Patterns: Elements of Reusable Object-Oriented Software", 43.19)); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books.add(new Book("978-0596527341", "Information Architecture for the World Wide Web: Designing Large-Scale Web Sites", 25.19)); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; books.add(new Book("978-0735605350", "Software Estimation: Demystifying the Black Art", 25.19)); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return SUCCESS; &nbsp;&nbsp; } } 
 清单3 WebContent/Ognl.jsp 
 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，至于Book的代码大家可以在我前一文章《在Struts 2中实现CRUD》看到。 
 下面是Ognl.jsp的代码，内容如下： 
 &lt;%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %&gt; &lt;%@ taglib prefix="s" uri="/struts-tags" %&gt; 
 &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "<a href="http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" rel="nofollow">http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd</a>"&gt; &lt;html xmlns="<a href="http://www.w3.org/1999/xhtml" rel="nofollow">http://www.w3.org/1999/xhtml</a>"&gt; &lt;head&gt; &nbsp;&nbsp;&nbsp; &lt;title&gt;Struts OGNL Demo&lt;/title&gt; &lt;/head&gt; &lt;body&gt;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &lt;h3&gt;访问OGNL上下文和Action上下文&lt;/h3&gt; &nbsp;&nbsp; &lt;p&gt;parameters:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;s:property value="#parameters.userName" /&gt;&lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;request.userName:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;s:property value="#request.userName" /&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;session.userName:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;s:property value="#session.userName" /&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;application.userName: &lt;s:property value="#application.userName" /&gt; &lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;attr.userName:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;s:property value="#attr.userName" /&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;hr /&gt; &nbsp;&nbsp;&nbsp; &lt;h3&gt;用于过滤和投影（projecting)集合&lt;/h3&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;Books more than $35&lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;ul&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;s:iterator value="books.{?#this.price &gt; 35}"&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;li&gt;&lt;s:property value="title" /&gt; - $&lt;s:property value="price" /&gt;&lt;/li&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/s:iterator&gt; &nbsp;&nbsp;&nbsp; &lt;/ul&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;The price of "Code Complete, Second Edition" is: 
 &nbsp;&nbsp;&nbsp;&nbsp; &lt;s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/&gt;&lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;hr /&gt; &nbsp;&nbsp;&nbsp; &lt;h3&gt;构造Map&lt;/h3&gt; &nbsp;&nbsp;&nbsp; &lt;s:set name="foobar" value="#{'foo1':'bar1', 'foo2':'bar2'}" /&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;The value of key "foo1" is &lt;s:property value="#foobar['foo1']" /&gt;&lt;/p&gt; &lt;/body&gt; &lt;/html&gt; 
 清单4 src/struts.xml 
 以上代码值得注意的是“&lt;s:property value="books.{?#this.title=='Code Complete, Second Edition'}.{price}[0]"/&gt;”，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。 
 最后是Struts 2的配置文件struts.xml，内容如下： 
 &lt;?xml version="1.0" encoding="UTF-8"?&gt; 
 &lt;!DOCTYPE struts PUBLIC &nbsp;&nbsp;&nbsp; "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" &nbsp;&nbsp;&nbsp; "<a href="http://struts.apache.org/dtds/struts-2.0.dtd" rel="nofollow">http://struts.apache.org/dtds/struts-2.0.dtd</a>"&gt; 
 &lt;struts&gt; &nbsp;&nbsp;&nbsp; &lt;constant name="struts.devMode" value="true" /&gt; &nbsp;&nbsp;&nbsp; &lt;package name="Struts2_OGNL_DEMO" extends="struts-default"&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;action name="Ognl" class="tutorial.action.OgnlAction"&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;result&gt;/Ognl.jsp&lt;/result&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/action&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &lt;/package&gt; &lt;/struts&gt; 
 清单5 示例运行结果1 
 发布运行应用程序，结果如下所示： 
 <img src="http://hiphotos.baidu.com/%EE%D1%D7%D300544/pic/item/d2ec9f97b9b21c4254fb963a.jpg" alt=""> 清单6 演示%用途的代码片段 
 “%”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： 
 &lt;hr /&gt; &nbsp;&nbsp;&nbsp; &lt;h3&gt;%的用途&lt;/h3&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;&lt;s:url value="#foobar['foo1']" /&gt;&lt;/p&gt; &nbsp;&nbsp;&nbsp; &lt;p&gt;&lt;s:url value="%{#foobar['foo1']}" /&gt;&lt;/p&gt; 
 清单7 示例运行结果2 
 刷新页面，结果如下所示： 
 <img src="http://hiphotos.baidu.com/%EE%D1%D7%D300544/pic/item/ca85b0239236776193580707.jpg" alt=""> 
 清单8 演示$用途的代码片段 
 “$”有两个主要的用途 
 1.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 用于在国际化资源文件中，引用OGNL表达式，例子请参考《在Struts 2.0中国际化(i18n)您的应用程序》 
 2.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 在Struts 2配置文件中，引用OGNL表达式，如 
 &lt;action name="AddPhoto" class="addPhoto"&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;interceptor-ref name="fileUploadStack" /&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;result type="redirect"&gt;ListPhotos.action?albumId=${albumId}&lt;/result&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;/action&gt; 
 清单9 src/bean/Book.java 
 public class Book { 
 private String isbn; private String title; private double price; 
 public Book(String isbn, String title, double price) { &nbsp;&nbsp; super(); &nbsp;&nbsp; this.isbn = isbn; &nbsp;&nbsp; this.price = price; &nbsp;&nbsp; this.title = title; } 
 public String getIsbn() { &nbsp;&nbsp; return isbn; } 
 public void setIsbn(String isbn) { &nbsp;&nbsp; this.isbn = isbn; } 
 public String getTitle() { &nbsp;&nbsp; return title; } 
 public void setTitle(String title) { &nbsp;&nbsp; this.title = title; } 
 public double getPrice() { &nbsp;&nbsp; return price; } 
 public void setPrice(double price) { &nbsp;&nbsp; this.price = price; } 
 } 
 总结 
 OGNL是一种功能很大的表达式语言，熟悉它可以使我们的开发变得更快捷。 
 </div> </td> 
 </tr> 
 </tbody> 
</table>