（四）值栈与OGNL

所有的学习我们必须先搭建好Struts2的环境（1、导入对应的jar包，2、web.xml，3、struts.xml）

第一节：值栈简介

值栈是对应每个请求对象的一套内存数据的封装，Struts2 会给每个请求创建一个新的值栈。

值栈能够线程安全地为每个请求提供公共的数据存取服务。

第二节：OGNL 引入

OGNL 是对象图导航语言Object-Graph Navigation Language 的缩写，它是一种功能强大的表达式语言。

OGNL 访问ValueStack 数据

　　<s:property value=”account” />

　　注：这里要添加<%@taglib prefix="s" uri="/struts-tags" %>struts的标签库

OGNL 访问ActionContext 数据

　　访问某个范围下的数据要用#

　　　　#parameters 请求参数request.getParameter(...)；

　　　　#request 请求作用域中的数据request.getAttribute(...)；

　　　　#session 会话作用域中的数据session.getAttribute(...)；

　　　　#application 应用程序作用域中的数据application.getAttribute(...)；

　　　　#attr 按照page request session application 顺序查找值

例子：

 struts.xml
 1 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE struts PUBLIC
     "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
     "http://struts.apache.org/dtds/struts-2.0.dtd">
 
 <struts>
 
   <package name="manage" namespace="/" extends="struts-default">
 
       <action name="hello" class="com.wishwzp.action.HelloAction">
           <result name="success" >success.jsp</result>
       </action>
   </package>
 
 </struts>

 HelloAction.java
 1 package com.wishwzp.action;
 
 import java.util.Map;
 
 import com.opensymphony.xwork2.ActionContext;
 import com.opensymphony.xwork2.ActionSupport;
 import com.opensymphony.xwork2.util.ValueStack;
 
 public class HelloAction extends ActionSupport{
 
     /**
      *
      */
     private static final long serialVersionUID = 1L;
 
     @Override
     public String execute() throws Exception {
         // 获取ActionContext
         ActionContext actionContext=ActionContext.getContext();
         // 获取狭义上的值栈
         // 值栈是用来存储数据的
         ValueStack valueStack=actionContext.getValueStack();
         valueStack.set("name", "张三(valueStack)");
         valueStack.set("age", 11);
 
         Map<String, Object> session=actionContext.getSession();
         session.put("name", "王五(session)");
         session.put("age", 13);
 
         Map<String, Object> application=actionContext.getApplication();
         application.put("name", "赵六(application)");
         application.put("age", 14);
         return SUCCESS;
     }
 }

 success.jsp
 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@taglib prefix="s" uri="/struts-tags" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Insert title here</title>
 <%
     request.setAttribute("name", "李四(request)");
     request.setAttribute("age", "12");
 %>
 </head>
 <body>
 获取狭义上的值栈数据：<s:property value="name"/>
                 <s:property value="age"/><br/>
 请求参数：<s:property value="#parameters.name"/>
        <s:property value="#parameters.age"/><br/>
 request：<s:property value="#request.name"/>
         <s:property value="#request.age"/><br/>
 session：<s:property value="#session.name"/>
         <s:property value="#session.age"/><br/>
 application：<s:property value="#application.name"/>
             <s:property value="#application.age"/><br/>
 attr取值：<s:property value="#attr.name"/>
         <s:property value="#attr.age"/><br/>
 </body>
 </html>

url:http://localhost:8080/Struts2Chap04/hello?name=ssss&age=23

结果：

第三节：OGNL 访问复杂对象

1，访问javaBean 对象；

2，访问集合对象；

3，访问Map 对象；

例子：

 struts.xml
 1 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE struts PUBLIC
     "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
     "http://struts.apache.org/dtds/struts-2.0.dtd">
 
 <struts>
 
   <package name="manage" namespace="/" extends="struts-default">
 
       <action name="hello" class="com.wishwzp.action.HelloAction">
           <result name="success" >success.jsp</result>
       </action>
   </package>
 
 </struts>

 Student.java
 1 package com.wishwzp.model;
 
 public class Student {
 
     private String name;
     private int age;
 
     public Student() {
         super();
         // TODO Auto-generated constructor stub
     }
     public Student(String name, int age) {
         super();
         this.name = name;
         this.age = age;
     }
 
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
 
 }

 HelloAction.java
 1 package com.wishwzp.action;
 
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
 import com.wishwzp.model.Student;
 import com.opensymphony.xwork2.ActionContext;
 import com.opensymphony.xwork2.ActionSupport;
 import com.opensymphony.xwork2.util.ValueStack;
 
 public class HelloAction extends ActionSupport{
 
     /**
      *
      */
     private static final long serialVersionUID = 1L;
 
     //访问javaBean对象,并get...和set...
     private Student student;
 
     //访问集合对象,并get...和set...
     private List<Student> students;
 
     //访问Map对象,并get...和set...
     private Map<String,Student> studentMap;
 
     public Map<String, Student> getStudentMap() {
         return studentMap;
     }
 
     public void setStudentMap(Map<String, Student> studentMap) {
         this.studentMap = studentMap;
     }
 
     public List<Student> getStudents() {
         return students;
     }
 
     public void setStudents(List<Student> students) {
         this.students = students;
     }
 
     public Student getStudent() {
         return student;
     }
 
     public void setStudent(Student student) {
         this.student = student;
     }
 
     @Override
     public String execute() throws Exception {
 
         //javaBean对象
         student=new Student("小扒", 12);
 
         //集合对象
         students=new ArrayList<Student>();
         students.add(new Student("老九",13));
         students.add(new Student("老十",14));
 
         //Map对象
         studentMap=new HashMap<String,Student>();
         studentMap.put("goodStudent", new Student("学霸",20));
         studentMap.put("badStudent", new Student("学渣",19));
         return SUCCESS;
     }
 
 }

 success.jsp
 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@taglib prefix="s" uri="/struts-tags" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Insert title here</title>
 </head>
 <body>
 ognl访问javaBean对象：<s:property value="student.name"/>
                     <s:property value="student.age"/><br/>
 
 ognl访问List集合：<s:property value="students[0].name"/>
                 <s:property value="students[0].age"/><br/>
                 <s:property value="students[1].name"/>
                 <s:property value="students[1].age"/><br/>
 
 ognl访问Map：<s:property value="studentMap['goodStudent'].name"/>
             <s:property value="studentMap['goodStudent'].age"/><br/>
             <s:property value="studentMap['badStudent'].name"/>
             <s:property value="studentMap['badStudent'].age"/><br/>
 </body>
 </html>

url访问：http://localhost:8080/Struts2Chap04/hello

结果：

第四节：OGNL 访问静态方法和属性

1，访问静态属性；

2，访问静态方法；需要在struts.xml加上<constant name="struts.ognl.allowStaticMethodAccess" value="true"></constant>

例子：

 struts.xml
 1 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE struts PUBLIC
     "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
     "http://struts.apache.org/dtds/struts-2.0.dtd">
 
 <struts>
 
     <constant name="struts.ognl.allowStaticMethodAccess" value="true"></constant>
 
   <package name="manage" namespace="/" extends="struts-default">
 
   </package>
 
 </struts>

 MyStatic.java
 1 package com.wishwzp.common;
 
 public class MyStatic {
 
     //静态属性
     public static final String str="Struts2开心学习";
 
     //静态方法
     public static String printUrl(){
         System.out.println("http://www.baidu.com");
         return "http://www.baidu.com";
     }
 }

 ognl_static.jsp
 1 <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@taglib prefix="s" uri="/struts-tags" %>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Insert title here</title>
 </head>
 <body>
 访问静态属性： <s:property value="@com.wishwzp.common.MyStatic@str"/><br/>
 访问静态方法：<s:property value="@com.wishwzp.common.MyStatic@printUrl()"/>
 </body>
 </html>

url:http://localhost:8080/Struts2Chap04/ognl_static.jsp

结果：