OGNL使用詳解二：Struts2的OGNL應用

                                OGNL使用詳解二：Struts2的OGNL應用

        在上一篇的博文基礎上，現在來看一下OGNL在Struts2中的應用。

        在上一篇文章中，我提到了，OgnlContext有一個稱之爲root的根對象，ognl取值默認從root中取。

        而在Struts2中的根對象就是：ValueStack（請記住，在Struts2中，OnglContext的root對象永遠都是ValueStack）

        現在來解釋一下ValueStack是什麼。

        在Struts2中，ValueStack是一個值棧接口，可以將多個bean壓進ValueStack中。可以使用EL表達式來取出ValueStack裏面的東西與計算等等。ValueStack作爲一個棧，放進去對象後。在查找時，必須從棧頂向棧底查找，一旦在棧頂查找到了，直接返回，不會再向棧底方向繼續查找了。例如：先放了一個person對象（屬性：name,address）,再放了一個dog對象（屬性：name,size）。此時查找name屬性，就會把dog的name屬性取出來。查找address時，dog沒找到這個屬性，纔會向棧底方向繼續查找，找到person的address並返回。如果查找person對象的name，[1].name，過濾棧頂元素，從棧頂第二個元素開始的棧裏面尋找name屬性，就會找到了。

        現在再來介紹一下ValueStack子棧的概念，在ValueStack中，棧頂元素索引是0，棧底元素索引是n。[0]返回從第0個元素到第n個元素的子棧，即當前的ValueStack。[2]返回從第3個元素到第n個元素的子棧.用這個方式過濾棧頂的部分元素，達到查找某個屬性的效果。

        在Struts2中， OgnlValueStack實現了ValueStack接口，而在ValueStack中，在Struts2的任何流程中，ValueStack中最頂層的對象一定是action對象。因此在jsp用OGNL直接寫某個action的屬性可以直接取值。就是因爲ValueStack是OgnlContext的根對象，無需寫#，默認就是根對象ValueStack。而action對象永遠是ValueStack的棧頂元素，所以我們寫一個屬性名字，就會從action對象中取出來了。如果這個action中沒這個 屬性，纔會往下面找。

Struts2在OgnlContext中初始化放進去了幾個命名對象（沒有放在跟對象ValueStack中，而是放在OgnlContext中，與ValueStack平級）：request，application，parameters，session,attr 。
parameters:用戶向action訪問攜帶的參數，例如：#parameters.username（相當於request.getParameter("username")）
request:jsp內置對象之一，例如：#parameters.username（相當於request.getAttribute("username")） 
session:jsp內置對象之一，例如：#session.username（相當於session.getAttribute("username")） 
application:jsp內置對象之一，例如：#application.username（相當於application.getAttribute("username")）
<attr:不是一個實際的對象，在查找時，現在pageContext當前頁面中找，再去request，再去session,再去application找，例如：#attr.username

        好了，說了這麼多，太枯燥了，直接上代碼！

        首先看一下bean實體的兩個類：

   

<span style="font-size:24px;">package struts2.ognl.bean;

/**
 * 
 * @author wangjian
 * 
 */
public class Cat {
	private String name;

	private int age;

	private String color;

	public Cat(String name, int age, String color) {
		this.name = name;
		this.age = age;
		this.color = color;
	}

	public Cat() {

	}

	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;
	}

	public String getColor() {
		return color;
	}

	public void setColor(String color) {
		this.color = color;
	}

}
</span>

<span style="font-size:24px;">package struts2.ognl.bean;

import java.util.Map;

/**
 * 
 * @author wangjian
 * 
 */
public class Person {
	private String name;

	private int age;

	private String address;

	private String[] friends;

	private Cat cat;

	private Map<String, String> map;

	public Person(String name, int age, String address, String[] friends,
			Cat cat, Map<String, String> map) {
		this.name = name;
		this.age = age;
		this.address = address;
		this.friends = friends;
		this.cat = cat;
		this.map = map;
	}

	public Person() {

	}

	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;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	public String[] getFriends() {
		return friends;
	}

	public void setFriends(String[] friends) {
		this.friends = friends;
	}

	public Cat getCat() {
		return cat;
	}

	public void setCat(Cat cat) {
		this.cat = cat;
	}

	public Map<String, String> getMap() {
		return map;
	}

	public void setMap(Map<String, String> map) {
		this.map = map;
	}

}
</span>

        接下來看一下action：

<span style="font-size:24px;">

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.struts2.interceptor.ApplicationAware;
import org.apache.struts2.interceptor.RequestAware;
import org.apache.struts2.interceptor.SessionAware;

import struts2.ognl.bean.Cat;
import struts2.ognl.bean.Person;

import com.opensymphony.xwork2.ActionSupport;

/**
 * 
 * @author wangjian
 * 
 */
public class OgnlAction extends ActionSupport implements RequestAware,
		SessionAware, ApplicationAware {

	private String username;

	private String password;

	private Map<String, Object> requestMap;

	private Map<String, Object> sessionMap;

	private Map<String, Object> applicationMap;

	private List<Person> list;

	public List<Person> getList() {
		return list;
	}

	public void setList(List<Person> list) {
		this.list = list;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public void setRequest(Map<String, Object> arg0) {
		System.out.println("setRequest invoked");

		this.requestMap = arg0;
	}

	public void setSession(Map<String, Object> arg0) {
		System.out.println("setSession invoked!");

		this.sessionMap = arg0;
	}

	public void setApplication(Map<String, Object> arg0) {
		this.applicationMap = arg0;
	}

	@Override
	public String execute() throws Exception {
		Thread.sleep(20000);

		requestMap.put("hello", "world");
		sessionMap.put("hello", "hello");
		applicationMap.put("hello", "hello world");

		Cat cat1 = new Cat("cat1", 20, "red");
		Cat cat2 = new Cat("cat2", 30, "blue");

		String[] friends1 = { "test1", "test2", "test3" };
		String[] friends2 = { "welcome1", "welcome2", "welcome3" };

		Map<String, String> map1 = new HashMap<String, String>();
		Map<String, String> map2 = new HashMap<String, String>();

		map1.put("test1", "test1");
		map1.put("test2", "test2");

		map2.put("hello1", "hello1");
		map2.put("hello2", "hello2");

		Person person1 = new Person("zhangsan", 20, "beijing", friends1, cat1,
				map1);
		Person person2 = new Person("lisi", 30, "shanghai", friends2, cat2,
				map2);

		list = new ArrayList<Person>();

		list.add(person1);
		list.add(person2);

		return SUCCESS;
	}
}
</span>

   下面來看一下在jsp網頁中，如何通過OGNL來取得action傳過來的信息。

 

<span style="font-size:24px;"><%@ page language="java"
	import="java.util.*, com.opensymphony.xwork2.* "
	pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags"%>


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>OGNL(Object Graph Navigation Language)對象圖導航語言OGNL</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">


</head>

<body>

	<br>username:
	<s:property value="username" />
	<br> password:
	<s:property value="password" />
	<br> ----------------------------------------
	<br> username:
	<s:property value="#parameters.username" />
	<br> password:
	<s:property value="#parameters.password" />
	<br> ----------------------------------------

	<br> request:
	<s:property value="#request.hello" />
	<br> session:
	<s:property value="#session.hello" />
	<br> application:
	<s:property value="#application.hello" />
	<br> attr:
	<s:property value="#attr.hello" />
	<br> ----------------------------------------

	<br> request:
	<%=((Map) ActionContext.getContext().get("request"))
					.get("hello")%><br> session:
	<%=ActionContext.getContext().getSession().get("hello")%><br>
	application:
	<%=ActionContext.getContext().getApplication().get("hello")%><br>
	attr:
	<%=((Map) ActionContext.getContext().get("attr"))
					.get("hello")%>
	<br> ----------------------------------------

	<br> person1: address:
	<s:property value="list[0].address" />
	<br> person2: age:
	<s:property value="list[1].age" />
	<br> person1: cat1: name:
	<s:property value="list[0].cat.name" />
	<br> size:
	<s:property value="list.size" />
	<br> isEmpty:
	<s:property value="list.isEmpty()" />
	<br> ----------------------------------------

	<br> person1: address:
	<%=((OgnlAction) ActionContext.getContext().getValueStack()
					.peek()).getList().get(0).getAddress()%><br> person2: age:
	<%=((OgnlAction) ActionContext.getContext().getValueStack()
					.peek()).getList().get(1).getAge()%><br> person1: cat1: name:
	<%=((OgnlAction) ActionContext.getContext().getValueStack()
					.peek()).getList().get(0).getCat().getName()%><br>

	----------------------------------------

	<br> person2:friend:
	<s:property value="list[1].friends[2]" />
	<br> person2:friend:
	<%=((OgnlAction) ActionContext.getContext().getValueStack()
					.peek()).getList().get(1).getFriends()[2]%><br>

	----------------------------------------

	<br> person2: map2:
	<s:property value="list[1].map['hello2']" />
	<br> ----------------------------------------
	<br> filtering:

	<s:property value="list.{? #this.name.length() > 2}[1].name" />
	<br> ----------------------------------------
	<br>

	<s:iterator value="list.{? #this.name.length() > 2}">

		<s:property value="name" />
		<br>
		<s:property value="cat.color" />
		<br>
		<s:property value="friends[0]" />
		<br>

	</s:iterator>

	----------------------------------------
	<br> projection:
	<br>

	<s:iterator value="list.{age}">

		<s:property />
		<br>

	</s:iterator>

</body>
</html>
</span>