OGNL入门(转)
来源:互联网 发布:灯光矩阵 编辑:程序博客网 时间:2024/06/11 09:48
- package org.darkness.ognl.test;
- import java.util.ArrayList;
- import java.util.HashMap;
- import java.util.List;
- import java.util.Map;
- import junit.framework.TestCase;
- import ognl.Ognl;
- import org.darkness.oa.model.Person;
- import org.darkness.oa.model.User;
- public class OgnlTest extends TestCase {
- // ***************** root对象的概念 ******************* //
- public void testOgnl_01() throws Exception{
- User user = new User();
- user.setUsername("暗之幻影");
- //相当于调用user.getUsername()方法
- String value = (String)Ognl.getValue("username", user);
- System.out.println(value);
- }
- public void testOgnl_02() throws Exception{
- User user = new User();
- Person p = new Person();
- p.setName("暗之幻影");
- user.setPerson(p);
- //相当于调用user.getPerson().getName()方法
- String value = (String)Ognl.getValue("person.name", user);
- System.out.println(value);
- }
- public void testOgnl_03() throws Exception{
- User user = new User();
- Person p = new Person();
- p.setName("暗之幻影");
- user.setPerson(p);
- //可以使用#root来引用根对象,相当于调用user.getPerson().getName()方法
- String value = (String)Ognl.getValue("#root.person.name", user);
- System.out.println(value);
- }
- // *********************** context的概念 **********************//
- public void testOgnl_04() throws Exception{
- Person p1 = new Person();
- Person p2 = new Person();
- p1.setName("风");
- p2.setName("云");
- Map<String,Person> context = new HashMap<String,Person>();
- context.put("p1", p1);
- context.put("p2", p2);
- // 需要加上#才表示到context中取数据,否则表示从根目录下取值
- String value = (String)Ognl.getValue("#p1.name + ',' + #p2.name", context, new Object());
- System.out.println(value);
- }
- public void testOgnl_05() throws Exception{
- Person p1 = new Person();
- Person p2 = new Person();
- p1.setName("风");
- p2.setName("云");
- Map<String,Person> context = new HashMap<String,Person>();
- context.put("p1", p1);
- context.put("p2", p2);
- User root = new User();
- root.setUsername("雨");
- String value = (String)Ognl.getValue("#p1.name + ',' + #p2.name + ',' + username", context, root);
- System.out.println(value);
- }
- // ******************* OGNL赋值操作 ************************//
- public void testOgnl_06() throws Exception{
- User user = new User();
- //给root对象的属性赋值,相当于调用user.setUsername()
- Ognl.setValue("username", user, "暗之幻影");
- System.out.println(user.getUsername());
- }
- public void testOgnl_07() throws Exception{
- User user = new User();
- Map<String, User> context = new HashMap<String, User>();
- context.put("u", user);
- //给context中的对象属性赋值,相当于调用user.setUsername()
- Ognl.setValue("#u.username", context, new Object(), "暗之幻影");
- System.out.println(user.getUsername());
- }
- public void testOgnl_08() throws Exception{
- User user = new User();
- Map<String, User> context = new HashMap<String, User>();
- context.put("u", user);
- //给context中的对象属性赋值,相当于调用user.setUsername()
- //在表达式中使用=赋值操作符来赋值
- Ognl.getValue("#u.username = '暗之幻影'",context, new Object());
- System.out.println(user.getUsername());
- }
- public void testOgnl_09() throws Exception{
- User user = new User();
- Person p = new Person();
- Map<String,Object> context = new HashMap<String,Object>();
- context.put("u", user);
- context.put("p", p);
- //给context中的对象属性赋值,相当于调用user.setUsername()
- //在表达式中使用=赋值操作符来赋值
- Ognl.getValue("#u.username = '风',#p.name = '云'",context, new Object());
- System.out.println(user.getUsername()+","+p.getName());
- }
- //****************** 使用OGNL调用对象的方法 **********************//
- public void testOgnl_10() throws Exception{
- User user = new User();
- user.setUsername("暗之幻影");
- String value = (String)Ognl.getValue("getUsername()", user);
- System.out.println(value);
- }
- public void testOgnl_11() throws Exception{
- User user = new User();
- Ognl.getValue("setUsername('暗之幻影')", user);
- System.out.println(user.getUsername());
- }
- // ******************* OGNL调用类变量、静态方法 *************************//
- public void testOgnl_12() throws Exception{
- User user = new User();
- Ognl.getValue("setUsername('暗之幻影')", user);
- Ognl.getValue("@System@out.println(username)", user);
- }
- public void testOgnl_13() throws Exception{
- User user = new User();
- Ognl.getValue("setUsername('暗之幻影')", user);
- Ognl.getValue("@System@out.println(@org.darkness.struts2.test.Utils@toLowerCase(username))", user);
- }
- // ********************* OGNL中的this表达式 **********************//
- public void testOgnl_14() throws Exception{
- Object root = new Object();
- Map context = new HashMap();
- List values = new ArrayList();
- for(int i=0; i<11; i++){
- values.add(i);
- }
- context.put("values", values);
- Ognl.getValue("@System@out.println(#values.size.(#this > 10 ? /"大于10/" : '不大于10'))", context, root);
- }
- public void testOgnl_15() throws Exception{
- User user = new User();
- Ognl.getValue("setUsername('暗之幻影')", user);
- Ognl.getValue("@System@out.println(#this.username)", user);
- }
- public void testOgnl_16() throws Exception{
- User user = new User();
- Ognl.getValue("setUsername('暗之幻影')", user);
- Ognl.getValue("@System@out.println(username.(#this.toLowerCase()))", user);
- }
- // ******************* 如何把表达式的解释结果作为另外一个表达式,OGNL中括号的使用 **********************//
- public void testOgnl_17() throws Exception{
- Object root = new Object();
- Map context = new HashMap();
- User u = new User();
- u.setUsername("暗之幻影");
- context.put("u", u);
- context.put("fact", "username");
- /**
- * 1、首先把#fact表达式进行解释,得到一个值:username
- * 2、解释括号中的表达式#u,其结果是user对象
- * 3、把括号中表达式的结果作为root对象,解释在第一步中得到的结果(即把第一步的结果看成另外一个表达式)
- */
- String value = (String)Ognl.getValue("#fact(#u)", context, root);
- System.out.println(value);
- }
- public void testOgnl_18() throws Exception{
- Person person = new Person();
- Map context = new HashMap();
- User u = new User();
- u.setUsername("暗之幻影");
- context.put("u", u);
- /**
- * 相当于调用person这个根对象的fact方法,并把#u的解释结果作为参数传入此方法
- */
- String value = (String)Ognl.getValue("fact(#u)", context, person);
- System.out.println(value); //输出是 "暗之幻影,"
- }
- public void testOgnl_19() throws Exception{
- Person person = new Person();
- Map context = new HashMap();
- User u = new User();
- u.setUsername("暗之幻影");
- context.put("u", u);
- /**
- * 1、先计算表达式fact,得到结果是:username
- * 2、解释括号中的表达式#u,其结果是user对象
- * 3、把括号中表达式的结果作为root对象,解释在第一步中得到的结果(即把第一步的结果看成另外一个表达式)
- */
- String value = (String)Ognl.getValue("(fact)(#u)", context, person);
- System.out.println(value); //输出"暗之幻影"
- }
- // ********************* OGNL访问集合元素 **************************//
- public void testOgnl_20() throws Exception{
- Object root = new Object();
- Map context = new HashMap();
- //用OGNL创建List对象
- List listvalue = (List)Ognl.getValue("{123,'暗之幻影','风之水影'}", context, root);
- context.put("listvalue", listvalue);
- //用OGNL创建数组
- int[] intarray= (int[])Ognl.getValue("new int[]{23,45,67}", context, root);
- context.put("intarray", intarray);
- //用OGNL创建Map对象
- Map mapvalue = (Map)Ognl.getValue("#{'listvalue':#listvalue,'intarray':#intarray}", context, root);
- context.put("mapvalue", mapvalue);
- Ognl.getValue("@System@out.println(#listvalue[0])", context, root);
- Ognl.getValue("@System@out.println(#intarray[1])", context, root);
- Ognl.getValue("@System@out.println(#mapvalue['intarray'][2])", context, root);
- Ognl.getValue("@System@out.println(#mapvalue.intarray[0])", context, root);
- }
- }
经常有同事问我关于Struts2标签中,OGNL的使用问题,最近抽空整理了理解和使用OGNL的要点,分享一下
1、理解Struts2中的ValueStack
ValueStack实际是一个接口,在Struts2中利用OGNL时,实际上使用的是实现了该接口的OgnlValueStack类,这个类是Struts2利用OGNL的基础。OgnlValueStack类的主要属性关系图如下:
|
|--application
|
|--session
context map (OgnlValueStack属性)--|
|--value stack (OgnlValueStack的root属性,实际是个ArrayList)
|
|--request
|
|--parameters
|
|--attr (searches page, request, session, then application scopes)
OgnlValueStack类包含两个重要的属性,一个root和一个context。其中root本质上是一个ArrayList,而context是一个Map(更确切的说是一个OgnlContext对象)。在这个OgnlContext对象(context)中,有一个默认的顶层对象root,OGNL访问context中这个默认顶层对象中的元素时,是不需要#号的,直接通过元素的名称来进行访问,而访问其他对象时,如request、session、attr等,则需要#号引用。Struts2将OgnlValueStack的root对象赋值给了context中的root对象,在OgnlValueStack的root对象中,保存着调用Action的实例,因此,在页面上通过Struts2标签访问Action的属性时,就不需要通过#号来引用。
2、OgnlValueStack与ActionContext的关系
在Struts2中,OgnlValueStack是ActionContext的基础,在ActionContext中,有一个Map类型的属性context,而这个context就是OgnlValueStack的context对象,ActionContext中的getSession()、getApplication()等方法,底层都是通过context.get()来实现的。
OGNL全称为Object-Graph Navigation Language,是一种表达式语言(EL)。
EL的支持者认为,在JSP页面中应尽可能地避免 <% %> 这样的标记,而代之以Tag,以使页面更简洁,并体现页面与后台代码分离的设计原则。对此我持保留意见,因为我并不认为使用Tag后的页面的可读性要高于使用<% %>。
Struts 2支持如下几种EL:
- OGNL(Object-Graph Navigation Language): 可以方便地操作对象属性的开源表达式语言
- JSTL(JSP Standard Tag Library): JSP 2.0集成的标准的表达式语言
- Groovy: 基于Java平台的动态语言,它具有时下比较流行的动态语言(如Python、Ruby和Smarttalk等)的一些新特性
- Velocity: 严格来说不是表达式语言,它是一种基于Java的模板匹配引擎,据说其性能要比JSP好
Struts 2默认的表达式语言是OGNL,原因是它相对其它表达式语言具有下面几大优势:
- 支持对象方法调用,如xxx.doSomeSpecial();
- 支持类静态的方法调用和值访问,表达式的格式为@[类全名(包括包路径)]@[方法名 | 值名],例如: @java.lang.String@format('foo %s', 'bar')或 @tutorial.MyConstant@APP_NAME;
- 支持赋值操作和表达式串联,如price=100, discount=0.8, calculatePrice(),这个表达式会返回80;
- 访问OGNL上下文(OGNL context)和ActionContext;
- 操作集合对象。
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。下面我讲述这个问题:
4.1 “#”的用途
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:
- 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Ma, #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
过滤和投影(projecting)集合
如books.{?#this.price<100}
构造Map
如#{'foo1':'bar1', 'foo2':'bar2'}
在此我演示一下这三种用途:
Book.java
这是一个Bean,用于描述一本书的信息
package example;
public class Book {
private String isbn;
private String title;
private double price;
public Book() {
}
public Book(String isbn, String title, double price) {
this.isbn = isbn;
this.title = title;
this.price = price;
}
public String getIsbn() {
return isbn;
}
public void setIsbn(String isbn) {
this.isbn = isbn;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
}
BookDao.java
一个伪DAO类
package example;
import java.util.Collection;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
public class BookDao
{
private static final BookDao instance;
private static final ConcurrentMap<String, Book> data;
static {
instance = new BookDao();
data = new ConcurrentHashMap<String, Book>();
data.put("978-0735619678", new Book("978-0735619678", "Code Complete, Second Edition", 32.99));
data.put("978-0596007867", new Book("978-0596007867", "The Art of Project Management", 35.96));
data.put("978-0201633610", new Book("978-0201633610", "Design Patterns: Elements of Reusable Object-Oriented Software", 43.19));
data.put("978-0596527341", new Book("978-0596527341", "Information Architecture for the World Wide Web: Designing Large-Scale Web Sites", 25.19));
data.put("978-0735605350", new Book("978-0735605350", "Software Estimation: Demystifying the Black Art", 25.19));
}
private BookDao() {}
public static BookDao getInstance() {
return instance;
}
public Collection<Book> getBooks() {
return data.values();
}
public Book getBook(String isbn) {
return data.get(isbn);
}
public void storeBook(Book book) {
data.put(book.getIsbn(), book);
}
public void removeBook(String isbn) {
data.remove(isbn);
}
public void removeBooks(String[] isbns) {
for(String isbn : isbns) {
data.remove(isbn);
}
}
}
OgnlAction.java
演示OGNL的Servlet类
package example;
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 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;
}
}
Ognl.jsp
演示OGNL的JSP
<%@ 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" /> - ___FCKpd___3lt;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>
example.xml
struts2 的MVC配置文件
<action name="Ognl" class="example.OgnlAction">
<result>/Ognl.jsp</result>
</action>
4.2 %的用法
“%”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:
<h3>%的用途</h3>
<p><s:url value="#foobar['foo1']" /></p>
<p><s:url value="%{#foobar['foo1']}" /></p>
刷新页面,显示以下内容
%的用途
#foobar['foo1']
bar1
4.3 $的用法
“$”有两个主要的用途:
- 用于在国际化资源文件中,引用OGNL表达式
- 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>
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