ognl表达式

*******

1，

package junit.test;

import java.util.HashMap;
import java.util.Map;

import ognl.Ognl;
import ognl.OgnlException;

import org.junit.Test;

import com.maple.ognl.Animal;

public class OGNLTest {
    
    @Test
    public void test1(){
        Map<String,Object> context=new HashMap<String,Object>();
        
        Animal a1=new Animal("rabit1");
        Animal a2=new Animal("rabit2");
        Animal a3=new Animal("rabit3");
        Animal a4=new Animal("rabit4");
        
        context.put("aaa1", a1);
        context.put("aaa2", a2);
        context.put("aaa3", a3);
        
        try {
            Object value1=Ognl.getValue("name", context, a1);
            System.out.println(value1); //rabit1
            Object value2=Ognl.getValue("#aaa1.name", context,a1);
            System.out.println(value2);//rabit1
            
            Object value3=Ognl.getValue("#aaa1.name", context, a2);
            System.out.println(value3);//rabit1
            
　　　　　　//将a4作为root对象，获取a4对象的name属性，a4不在上下文中
            Object value4=Ognl.getValue("name", context, a4);
            System.out.println(value4);//rabit4
            
            Object value5=Ognl.getValue("#aaa4.name", context, a4);
            //System.out.println(value5); //抛异常
        } catch (OgnlException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

总结：对于使用上下文的ognl，若不指定从哪个对象中查找"name"属性，则默认从root对象中查找；

若指定了（通过#指定，如#aaa1，），则从指定对象中查找，如果指定对象不在上下文中，则ognlException异常，

 2，调用成员变量，静态方法，静态变量

@Test
    public void test2(){
        OgnlContext context=new OgnlContext();
        Animal a1=new Animal("ra1");
        Animal a2=new Animal("rabit2");
        Animal a3=new Animal("rabi3");
        
        context.put("aa1", a1);
        context.put("aa2", a2);
        context.put("aa3", a3);
        context.setRoot(a1);
        try {
            /*调用成员方法*/
            Object value=Ognl.getValue("name.length()",context,context.getRoot());
            System.out.println(value);//3
            Object value2=Ognl.getValue("#aa2.name.toUpperCase()", context,context.getRoot());
            System.out.println(value2); //RABIT2
            Object value3=Ognl.getValue("#aa3.name.charAt(2)", context,context.getRoot());
            System.out.println(value3); //b
            /*调用静态方法*/
            Object value4=Ognl.getValue("@java.lang.Math@min(2,4)", context,context.getRoot());
            System.out.println(value4);//2
            Object value5=Ognl.getValue("@java.lang.Math@E", context,context.getRoot());
            System.out.println(value5);//2.718281828459045
        } catch (OgnlException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

成员方法调用：方法名+()，参数直接写里面；

静态方法调用：@类全名@方法名()；

静态变量调用：@类全名@字段；

3，ognl操作集合对象

@Test
    public void test3(){
        Classroom classroom=new Classroom();
        classroom.getStudents().add("mary");
        classroom.getStudents().add("lenka");
        classroom.getStudents().add("linda");
        classroom.getStudents().add("dan");
        
        Student stu=new Student();
        stu.getContactWays().put("cell", "111");
        stu.getContactWays().put("phone", "222");
        stu.getContactWays().put("mobile", "333");
        
        OgnlContext context=new OgnlContext();
        context.put("classroom", classroom); //list
        context.put("student", stu); //map
        
        context.setRoot(classroom);
        try {
            Object collection=Ognl.getValue("students", context, context.getRoot());
            System.out.println(collection); //[mary, lenka, linda, dan]
            Object collection3=Ognl.getValue("students[0]", context, context.getRoot());
            System.out.println(collection3); //mary
            Object collection4=Ognl.getValue("students.size()", context, context.getRoot());
            System.out.println(collection4); //4
            
            
            Object collection2=Ognl.getValue("#student.contactWays", context, context.getRoot());
            System.out.println(collection2); //{phone=222, cell=111, mobile=333}
            Object collection5=Ognl.getValue("#student.contactWays['cell']", context, context.getRoot());
            System.out.println(collection5); //111
            Object collection6=Ognl.getValue("#student.contactWays['ff']", context, context.getRoot());
            System.out.println(collection6); //null
            
            Object createcol=Ognl.getValue("{'aa','bb','cc'}", context, context.getRoot());
            System.out.println(createcol);//[aa, bb, cc]
            Object createmap=Ognl.getValue("#{'k1':'v1','k2':'v2','k3':'v3'}", context, context.getRoot());
            System.out.println(createmap); //{k1=v1, k2=v2, k3=v3}
            
        } catch (OgnlException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }

public class Classroom {
    private List<String> students=new ArrayList<String>();

    public List<String> getStudents() {
        return students;
    }

    public void setStudents(List<String> students) {
        this.students = students;
    }
    
}

public class Student {
    private Map<String,Object> contactWays=new HashMap<String,Object>();
    /*private Map<String,Object> contactWays=new LinkedHashMap<String,Object>();保持插入顺序*/

    public Map<String, Object> getContactWays() {
        return contactWays;
    }

    public void setContactWays(Map<String, Object> contactWays) {
        this.contactWays = contactWays;
    }
    
}

总结：ognl认为List和Array是一样的，创建List集合使用{}，创建Map集合使用#{}

4,ognl投影和过滤集合

package com.maple.ognl;

import java.util.ArrayList;
import java.util.List;

public class Human {
    private String name;
    private String sex;
    private int age;
    private List<Human> friends=new ArrayList<Human>();
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public List<Human> getFriends() {
        return friends;
    }
    public void setFriends(List<Human> friends) {
        this.friends = friends;
    }
    public Human(String name, String sex, int age) {
        super();
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Human [name=" + name + ", sex=" + sex + ", age=" + age + "]";
    }
    public Human(){}
    
}

测试

//过滤集合，投影集合
    @Test
    public void test4(){
        OgnlContext context=new OgnlContext();
        
        Human human=new Human();
        human.setName("maple");
        human.setSex("female");
        human.setAge(22);
        human.getFriends().add(new Human("mary","fe",2));
        human.getFriends().add(new Human("linda","fe",2));
        human.getFriends().add(new Human("serlina","male",2));
        context.put("human", human);
        context.setRoot(human);
        try {
            Object filter=Ognl.getValue("friends.{? #this.name.length()>4}", context,context.getRoot());
            //[Human [name=linda, sex=fe, age=2], Human [name=serlina, sex=male, age=2]]
            System.out.println(filter);
            Object filter2=Ognl.getValue("friends.{name}", context,context.getRoot());
            System.out.println(filter2);//[mary, linda, serlina]
        
        } catch (OgnlException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

总结：ognl可以对集合进行投影和过滤，就相当于数据库对表取列和取行操作；

过滤语法：collection.{? expression}，#this表示集合当前对象

投影语法：collection.{expression}

5，ognl是怎样从VlaueStack中取值的

每当一个请求到达Action，Struts2会把Action对象压入栈中

<s:property value="username"/>

username:<%= (HelloWorldAction)ActionContext.getContext().getValueStack().peek().getUsername() %>

*******

参考地址：http://developer.51cto.com/art/201203/322509.htm