struts2值栈与OGNL

1. struts2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。

新建项目HeadFirstStruts2Chap04

2. struts2引入OGNL

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
<%@taglib prefix="s" uri="/struts-tags" %>
<s:property value="account"/>

OGNL访问ActionContext数据
访问某个范围下的数据要用#
#parameters.xxx 请求参数 request.getParameter(xxx);
#request.xxx 请求作用域中的数据 request.getAttribute(xxx);
#session.xxx 会话作用域中的数据 session.getAttribute(xxx);
#application.xxx 应用程序作用域中的数据 application.getAttribute(xxx);
#attr.xxx 按照page request session application顺序查找值

1) OGNL访问数据

HelloAction.java

package com.andrew.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 {
    @Override
    public String execute() throws Exception {
        ActionContext actionContext = ActionContext.getContext();
        // 获取狭义上的值栈
        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;
    }
}

struts.xml

<package name="manage" namespace="/" extends="struts-default">
      <action name="hello" class="com.andrew.action.HelloAction">
          <result name="success" >success.jsp</result>
      </action>
</package>

success.jsp

<%@taglib prefix="s" uri="/struts-tags" %>
<%
    request.setAttribute("name", "李四(request)");
    request.setAttribute("age", "12");
%>
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/>

http://localhost:8080/HeadFirstStruts2Chap04/hello
获取狭义上的值栈数据：张三(valueStack) 11
请求参数： 
request：李四(request) 12
session：王五(session) 13
application：赵六(application) 14
attr取值：李四(request) 12

2) 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；

Student.java

package com.andrew.model;
public class Student {
    private String name;
    private int age;
    public Student() {}
    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;
    }
}

StudentAction.java

package com.andrew.action;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.andrew.model.Student;
import com.opensymphony.xwork2.ActionSupport;
public class StudentAction extends ActionSupport {
    private Student student;
    private List<Student> students;
    private Map<String, Student> studentMap;
    public Student getStudent() {
        return student;
    }
    public void setStudent(Student student) {
        this.student = student;
    }
    public List<Student> getStudents() {
        return students;
    }
    public void setStudents(List<Student> students) {
        this.students = students;
    }
    public Map<String, Student> getStudentMap() {
        return studentMap;
    }
    public void setStudentMap(Map<String, Student> studentMap) {
        this.studentMap = studentMap;
    }
    @Override
    public String execute() throws Exception {
        student = new Student("小三", 12);
        students = new ArrayList<Student>();
        students.add(new Student("小四", 13));
        students.add(new Student("小五", 14));
        studentMap = new HashMap<String, Student>();
        studentMap.put("goodStudent", new Student("学霸", 20));
        studentMap.put("badStudent", new Student("学渣", 19));
        return SUCCESS;
    }
}

struts.xml

<package name="manage" namespace="/" extends="struts-default">
      <action name="student" class="com.andrew.action.StudentAction">
          <result name="success" >student.jsp</result>
      </action>
</package>

http://localhost:8080/HeadFirstStruts2Chap04/student
ognl访问javaBean对象：小三 12
ognl访问List集合：小四 13
小五 14
ognl访问Map：学霸 20
学渣 19

3) OGNL访问静态方法和属性

1. 访问静态属性；
2. 访问静态方法；
<constant name="struts.ognl.allowStaticMethodAccess" value="true"></constant>

MyStatic.java

package com.andrew.common;
public class MyStatic {
    public static final String str = "百度";
    public static String printUrl(){
        System.out.println("http://www.baidu.com");
        return "http://www.baidu.com";
    }
}

struts.xml

<constant name="struts.ognl.allowStaticMethodAccess" value="true"></constant>

ognl_static.jsp

<%@taglib prefix="s" uri="/struts-tags" %>
访问静态属性：<s:property value="@com.andrew.common.MyStatic@str"/><br/>
访问静态方法：<s:property value="@com.andrew.common.MyStatic@printUrl()"/>

http://localhost:8080/HeadFirstStruts2Chap04/ognl_static.jsp
访问静态属性：百度
访问静态方法：http://www.baidu.com