（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：