Struts2系列（四）OGNL表达式

一.OGNL表达式概述

Struts2支持OGNL表达式
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。
webwork2和现在的Struts2.x中使用OGNL取代原来的EL来做界面数据绑定，所谓界面数据绑定，也就是把界面元素（例如一个textfield,hidden)和对象层某个类的某个属性绑定在一起，修改和显示自动同步。

二.OGNL测试代码

直接上代码，具体解释见代码注释

OGNL.java

/*
OGNL表达式：对象视图导航语言
与EL表达式相似，但比EL表达式强大

关于EL表达式：
11大内置对象可以取值
requestscope
sessionscope
applicationscope
pagescope
pagecontext
params
paramvalues
header
headervalues
cookie
initparams

关于OGNL表达式：只有一个内置对象可以取值
OGNL context：OGNL上下文对象包括两部分
root部分：可以放置任何对象
context部分：只能放置map对象
 */

//测试OGNL
public class OGNL {
    @Test
    //OGNL操作代码演示
    public void funone() throws OgnlException{
        //准备root
        User root=new User("tom",18);
        //准备Context
        Map<String, User> context=new HashMap<String, User>();
        context.put("u1", new User("jake",19));
        context.put("u2", new User("rose",20));
        //准备OGNL context
        OgnlContext oc=new OgnlContext();
        oc.setRoot(root);
        oc.setValues(context);
        /*写OGNL*/
        //取出root中user对象的name属性
        //直接写属性
        String name= (String) Ognl.getValue("name", oc, oc.getRoot());
        System.out.println(name);
        //取出Context中user对象的name属性
        //#代表从context部分取值
        name= (String) Ognl.getValue("#u1.name", oc, oc.getRoot());
        System.out.println(name);
        //为root中user对象的name属性赋值
        name=  (String) Ognl.getValue("name='jerry'", oc, oc.getRoot());
        System.out.println(name);
        name= (String) Ognl.getValue("name", oc, oc.getRoot());
        System.out.println(name);
        //为Context中user对象的name属性赋值
        name= (String) Ognl.getValue("#u1.name='cat'", oc, oc.getRoot());
        System.out.println(name);
        name= (String) Ognl.getValue("#u1.name", oc, oc.getRoot());
        System.out.println(name);
        //调用root中user对象的方法
        name=  (String) Ognl.getValue("setName('lililili')", oc, oc.getRoot());
        System.out.println(name);
        name=  (String) Ognl.getValue("getName()", oc, oc.getRoot());
        System.out.println(name);
        //调用Context中user对象的方法
        name= (String) Ognl.getValue("#u1.setName('babababa')", oc, oc.getRoot());
        System.out.println(name);
        name= (String) Ognl.getValue("#u1.getName()", oc, oc.getRoot());
        System.out.println(name);
        //调用静态方法,得到返回值
        //@+全路径+@+方法名(参数)
        name=  (String) Ognl.getValue("@cjx.user.Util@echo('hello!')", oc, oc.getRoot());
        System.out.println(name);
        //得到静态属性
        double pi=  (double) Ognl.getValue("@java.lang.Math@PI", oc, oc.getRoot());
        System.out.println(pi);
        pi=  (double) Ognl.getValue("@@PI", oc, oc.getRoot());//java.lang.Math是内置对象
        System.out.println(pi);
        //创建对象之list对象
        Integer in= (Integer) Ognl.getValue("{'ab','bb','cb','db'}.size()", oc, oc.getRoot());
        System.out.println(in);
        name= (String) Ognl.getValue("{'ab','bb','cb','db'}[1]", oc, oc.getRoot());
        System.out.println(name);
        //创建对象map对象
        //#代表map对象
         in= (Integer) Ognl.getValue("#{'name':'tom','age':'18'}.size()", oc, oc.getRoot());
        System.out.println(in);
        name= (String) Ognl.getValue("#{'name':'tom','age':'18'}['name']", oc, oc.getRoot());
        System.out.println(name);
    }   
}

OgnlTestlAction.java

public class OgnlTestlAction extends ActionSupport{
    /*为什么OGNL表达式会取到值?
* OGNL与Struts2的整合
    Struts2为ognl准备了一个ValueStack对象,作为ognl取值范围
    ValueStack(ognl的取值域)
            |-Root      栈
            |-Context   ActionContext(数据中心)
    栈 => 默认放置当前访问的Action对象
    ActionContext 
            |- request
            |- response
            |- servletContext
            |- requestScope
            |- sessionScope
            |- applicationScope
            |- parameters
            |- attrs
*获得原生ServletAPI.详见/struts2/src/cjx/api/ServletAPI.java
    ActionContext 数据中心
        |-request
        |-response
        |-ServletContext
        |-requestScope
        |-sessionScope
        |-applicationScope
        |-params
        |-attrs
        ....
    //获得ActionContext
    ActionContext.getContext(); 
        |-requestScope
        |-sessionScope
        |-applicationScope
        |-params
        |-attrs
    //获得ActionContext中原生对象的工具类
    ServletActionContext
        |-request
        |-response
        |-ServletContext
*OGNL与Struts2结合的应用
    |- 参数接收 => struts2中的参数交给ognl引擎处理
    |- 配置文件中 => ${ognl表达式}
    |- 标签 => struts2标签

     */
    private String name;
    public String execute() throws Exception {
        System.out.println("OgnlTestlAction.得到name参数："+name);
        return "success";
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

OgnlActionStruts.xml

<?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" namespace="/ognl" extends="struts-default">
    <action  name="ognlaction" class="cjx.ojnl.OgnlAction" >
    <result name="success" type="redirectAction">
        <param name="actionName">ognltestaction</param>
        <param name="namespace">/ognl</param>
        <param name="name">${name}</param>
    </result>
    </action>

    <action  name="ognltestaction" class="cjx.ojnl.OgnlTestlAction" >
    <result name="success" >/ognl.jsp</result>
    </action>

    </package>
    </struts>

OgnlAction.java

public class OgnlAction extends ActionSupport{
/*在ognl.jsp中点击测试后
测试ognl:根据配置会先进入cjx.ojnl.OgnlAction
在cjx.ojnl.OgnlAction中为name属性赋值了
根据配置会redirectAction到ognltestaction
param属性中name属性在Struts2中不存在
所以Struts2会将其作为参数传递，利用ognl表达式取值
利用ognl表达式动态取值，地址栏会传递参数
 */
    private String name;
    public String execute() throws Exception {
        System.out.println("OgnlAction.name被赋值为:"+name);
        return "success";
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

ognl.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<form action="${pageContext.request.contextPath}/ognl/ognlaction" method="post">
<input type="text" name="name"><br>
<input type="submit" value="测试ognl" >
</form><br>
</body>
</html>

TagAction.java

public class TagAction extends ActionSupport{

    public String execute() throws Exception {
        List<String> list= new ArrayList<String>();
        list.add("tom");
        list.add("rose");
        list.add("jack");
        list.add("jerry");
        ActionContext.getContext().put("list", list);       
        this.addActionError("这是一个来自TagAction的错误信息！");       
        return SUCCESS;
    }           
}

TagActionStruts.xml

<?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="tag" namespace="/tag" extends="struts-default">  
    <action  name="tagaction" class="cjx.tag.TagAction" >
    <result name="success" >/tag.jsp</result>
    </action>   
</package>
    </struts>

tag.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@taglib prefix="s"  uri="/struts-tags"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>tag</title>
</head>
<body>
遍历标签iterator <br>
1.取栈顶元素<br>
<s:iterator value="#list">
<s:property/><br>
</s:iterator>
2.遍历元素<br>
<s:iterator value="#list" var="name">
<s:property value="#name"/><br>
</s:iterator>
3.计次遍历
<s:iterator begin="1" end="100" step="2">
<s:property/> -
</s:iterator><br>
if else elseif标签 <br>
<s:if test="#list.size()==4">
list长度为4<br>
</s:if>
<s:elseif test="#list.size()==5">
list长度为5<br>
</s:elseif>
<s:else>
list长度不为4和5<br>
</s:else>
取值标签property <br>
<s:property value="#list.size()"/><br>
<s:property value="#session.user.name"/><br>
<br>表单标签<br>
 form theme="simple"可以取消Struts2提供的样式
<s:form action="ognlaction" namespace="/ognl">
<s:textfield name="name" label="用户名" ></s:textfield>根据栈中的属性自动回显
<s:password name="password" label="密码"></s:password>
<s:radio list="#{1:'男',2:'女'}" name="sex" label="性别"></s:radio>
<s:checkboxlist list="{'运动','游戏'}" name="like"  label="爱好"></s:checkboxlist>
<s:select list="{'本科','硕士','院士'}"  headerKey="" headerValue="请选择"  name="edu" label="学历"></s:select>
<s:file name="photo" label="照片"></s:file>
<s:textarea name="desc" label="个人简历" ></s:textarea>
<s:submit value="提交"></s:submit>
</s:form>
<br>actionerror标签:取出错误信息<br>
<s:actionerror/><br>
</body>
</html>

User.java

public class User {

    private String name;
    private Integer age;
    private Date date;      
    public User() {
        super();
    }
    public User(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public Date getDate() {
        return date;
    }
    public void setDate(Date date) {
        this.date = date;
    }
    @Override
    public String toString() {
        return "User [name=" + name + ", age=" + age + ", date=" + date + "]";
    }   
}

Util.java

public class Util {
//回音方法，用于测试
public static Object echo(Object  o){
    return o;
    }
}

不要忘了主配置文件struts.xml

<?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>    
    <!-- 引入其他配置文件 -->   
    <include file="cjx/ojnl/OgnlActionStruts.xml"></include>
    <include file="cjx/tag/TagActionStruts.xml"></include>
    </struts>