Struts2入门03

三、Struts与OGNL

1、OGNL基本使用

OGNL:对象导航图语言/对象视图导航语言（Object Graph Navigation Language）

OGNL分为root与context区域,在Strtus2中，ValueStack就是OGNLContext

那么ValueStack中也就有root（栈）与context(ActionContext)

并且ActionContext与ValueStack是相互引用的，所以获取ValueStack的方式为：

ActionContext.getcontext().getValueStack();

root:存放当前Action对象(栈结构)

context:存放ActionContext

准备工作：
导包:struts2的默认包中已经包含了OGNL需要的jar包

public class OgnlDemo1 {

    //展示OGNL语法
    @Test
    public void fun1() throws Exception {
        //准备OGNLContext
        //准备root
        User rootUser=new User("tom",18,new Date());
        //准备context
        Map<String,User> context = new HashMap();
        context.put("user1", new User("jack",20,new Date()));
        context.put("user2", new User("rose",22,new Date()));
        
        OgnlContext oc = new OgnlContext();
        
        oc.setRoot(rootUser);
        oc.setValues(context);
        //书写OGNL
        
        //取root中user对象的name属性
        String name=(String) Ognl.getValue("name", context, oc.getRoot());
        System.out.println(name);
        int age=(int) Ognl.getValue("age", context,oc.getRoot());
        System.out.println(age);
        
        //取出contxt中的属性    #代表要从取值
        String name1=(String) Ognl.getValue("#user1.name", context, oc.getRoot());
        System.out.println(name1);
    }
    
    
    //基本语法演示
    //为属性赋值
    @Test
    public void fun2() throws Exception {
        //准备OGNLContext
        //准备root
        User rootUser=new User("tom",18,new Date());
        //准备context
        Map<String,User> context = new HashMap();
        context.put("user1", new User("jack",20,new Date()));
        context.put("user2", new User("rose",22,new Date()));
        
        OgnlContext oc = new OgnlContext();
        //将rootUser作为root部分
        oc.setRoot(rootUser);
        //将context作为context部分
        oc.setValues(context);
        //书写OGNL
        
                
        //OGNL修改值root
         Ognl.getValue("name='jerry'", context, oc.getRoot());
         //取值
         String name=(String)Ognl.getValue("name", context, oc.getRoot());
        System.out.println(name);
        
        //OGNL修改context 
         Ognl.getValue("#user1.name='张三',#user2.name='李四'",context, oc.getRoot());
        String cname=(String) Ognl.getValue("#user1.name",context, oc.getRoot());
        String cname1=(String)Ognl.getValue("#user2.name",context, oc.getRoot());
        System.out.println(cname+"_"+cname1);
        
        //OGNL调用方法 
        System.out.println(Ognl.getValue("getName()", context, oc.getRoot()));
        System.out.println(Ognl.getValue("#user1.setName('lucy'),#user1.getName()", context, oc.getRoot()));
        
        //OGNL调用静态方法 使用    @符号完整类名加上@方法名
        System.out.println(Ognl.getValue("@java.lang.Math@random()",context, oc.getRoot()));
        System.out.println(Ognl.getValue("@java.lang.Math@PI",context, oc.getRoot()));
        System.out.println(Ognl.getValue("@@PI",context, oc.getRoot()));
        


    }
    
    //OGNL创建对象
    @Test
    public void fun3() throws Exception 
    {
        OgnlContext oc = new OgnlContext();
        int num=(int) Ognl.getValue("{'tom','jerry','lucy','rose'}.size()", oc,oc.getRoot());
        String name=(String) Ognl.getValue("{'tom','jerry','lucy','rose'}[0]", oc,oc.getRoot());
        String name1=(String) Ognl.getValue("{'tom','jerry','lucy','rose'}.get(0)", oc,oc.getRoot());
//        System.out.println(num);
//        System.out.println(name);
//        System.out.println(name1);
        
        //创建Map集合 并取值
        int num1=(int) Ognl.getValue("#{'name':'tom','age':18}.size()", oc,oc.getRoot());
        String name2=(String) Ognl.getValue("#{'name':'tom','age':18}['name']", oc,oc.getRoot());
        int age=(int) Ognl.getValue("#{'name':'tom','age':18}.get('age')", oc,oc.getRoot());
        System.out.println(num1);
        System.out.println(age);
        
        
    }
    
}

 2、OGNL与Struts2结合

　　在配置文件中使用OGNL动态获取资料参数，需要在Action设置对应属性

public class ValueStackDemo extends ActionSupport {

    private String name;
    private String address;
    @Override
    public String execute() throws Exception 
    {
        ValueStack valueStack = ActionContext.getContext().getValueStack();

        name="zhangsan";
        address="重庆";

        
        return SUCCESS;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    
    
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
    "http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>
    <package name="ognl" extends="struts-default" namespace="/">
        <action name="valueS" class="Ognl.ValueStackDemo">
            <result name="success" type="redirectAction">
                <param name="actionName">valueST</param>
                <param name="namespace">/</param>
                <param name="name">${name}</param>
                <param name="address">${address}</param>
            </result>
        </action>
        
        <action name="valueST" class="Ognl.ValueSTest">            
        </action>
    </package>
</struts>
http://localhost:8080/Struts2_day01/valueST.action?name=zhangsan&address=重庆

3、Struts2中的request

由于request被struts2包装，在JSP页面获取ActionContext.getcontext().put(key,value)中的值的时候的获取顺序即request.getAttribute()的获取：

1、原生request域

2、查找ValueStack的栈部分(root)

3、查找ValueStack的context部分（ActionContext)

4、Struts2参数接受与OGNL

不管是属性驱动还是对象驱动还是模型驱动的方式获取参数，

其原理就是将获取到的页面参数放入栈中，再通过OGNL表达式赋值