【SSH】Struts2学习（三）OGNL、OGNL与Struts2结合

一、OGNL

1、OGNL概述

OGNL是Object-Graph Navigation Language的缩写，它是一种功能强大的表达式语言，通过它简单一致的表达式语法，可以存取对象的任意属性，调用对象的方法，遍历整个对象的结构图，实现字段类型转化等功能。它使用相同的表达式去存取对象的属性。

${user.addr.name}这种写法就叫对象视图导航，OGNL不仅仅可以视图导航，支持比EL更加丰富的功能

2、OGNL准备工作

（1）导包，struts2已经自带，无需重复导

（2）代码准备

@Test//准备工作public void fun1() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap<String,User> context = new HashMap<String,User>();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();//将rootUser作为root部分oc.setRoot(rootUser);//将context这个Map作为Context部分oc.setValues(context);//书写OGNLOgnl.getValue("", oc, oc.getRoot());}

3、OGNL基本语法

package com.sh.a_ognl;import java.util.HashMap;import java.util.Map;import org.junit.Test;import com.sh.bean.User;import ognl.Ognl;import ognl.OgnlContext;//展示OGNL语法public class Demo {@Test//准备工作public void fun1() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();//将rootUser作为root部分oc.setRoot(rootUser);//将context这个Map作为Context部分oc.setValues(context);//书写OGNLOgnl.getValue("", oc, oc.getRoot());}@Test//基本语法演示//取出root中的属性值public void fun2() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNL//取出root中user对象的name属性String name = (String) Ognl.getValue("name", oc, oc.getRoot());Integer age = (Integer) Ognl.getValue("age", oc, oc.getRoot());System.out.println(name);System.out.println(age);}@Test//基本语法演示//取出context中的属性值public void fun3() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNL//取出root中user对象的name属性String name = (String) Ognl.getValue("#user1.name", oc, oc.getRoot());Integer age = (Integer) Ognl.getValue("#user1.age", oc, oc.getRoot());System.out.println(name+":"+age);}@Test//基本语法演示//为属性赋值public void fun4() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNLOgnl.getValue("name='jerry'", oc,oc.getRoot());String name = (String) Ognl.getValue("name", oc, oc.getRoot());System.out.println(name);Ognl.getValue("#user1.name='麦客子'", oc,oc.getRoot());String name1 = (String) Ognl.getValue("#user1.name", oc, oc.getRoot());System.out.println(name1);}@Test//基本语法演示//调用方法public void fun5() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNLOgnl.getValue("setName('孙悟空')", oc, oc.getRoot());String name = (String) Ognl.getValue("getName()", oc, oc.getRoot());System.out.println(name);String name1 = (String) Ognl.getValue("#user1.setName('猪八戒'),#user1.getName()", oc, oc.getRoot());System.out.println(name1);}@Test//基本语法演示//调用静态方法public void fun6() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNLString name = (String) Ognl.getValue("@com.sh.a_ognl.HahaUtils@echo('hello java')", oc, oc.getRoot());/*double name1 = (double) Ognl.getValue("@ java.lang.Math@PI", oc, oc.getRoot());*/double name1 = (double) Ognl.getValue("@@PI", oc, oc.getRoot());System.out.println(name);System.out.println(name1);}@Test//基本语法演示//ognl创建对象list|mappublic void fun7() throws Exception{//准备ONGLContext//准备RootUser rootUser = new User("tom",18);//准备ContextMap context = new HashMap();context.put("user1", new User("jack",18));context.put("user2", new User("rose",22));OgnlContext oc = new OgnlContext();oc.setRoot(rootUser);oc.setValues(context);//书写OGNL//创建listInteger size = (Integer) Ognl.getValue("{'宝钗','黛玉','晴雯'}.size()", oc, oc.getRoot());String name = (String) Ognl.getValue("{'宝钗','黛玉','晴雯'}[0]", oc, oc.getRoot());String name2 = (String) Ognl.getValue("{'宝钗','黛玉','晴雯'}[0]", oc, oc.getRoot());System.out.println(size);System.out.println(name);System.out.println(name2);//创建mapInteger size2 = (Integer) Ognl.getValue("#{'name':'宝钗','age':'18'}.size()", oc, oc.getRoot());String name3 = (String) Ognl.getValue("#{'name':'宝钗','age':'18'}['name']", oc, oc.getRoot());Integer age = (Integer) Ognl.getValue("#{'name':'宝钗','age':18}.get('age')", oc, oc.getRoot());System.out.println(size2);System.out.println(name3);System.out.println(age);}}

二、Struts2与OGNL表达式的结合

1、结合原理

查看值栈两部分内容

Root

Context

2、栈的原理

3、浅尝值栈

(1)值栈的内部结构

在ValueStack的实现类OngValueStack中包含两部分，分别是值栈和Map

（2）ActionContext与ValueStrack的关系

4、Struts2与OGNL结合体现

（1）参数接收

获得值栈的2种方式：

（2）配置文件中

配置文件：

（3）Struts2标签

详见【SSH】Struts2学习（四）

参考源码：https://github.com/AmazeLee/Struts2.git

If we believe that tomorrow will be better, we can bear a hardship today. 

如果我们相信明天会更好，今天就能承受艰辛。