struts-核心内容-10-Ognl表达式语言

OGNL 对象图导航语言

Struts框架默认支持ognl表达式语言

作用-页面取值

ognl必须配合struts标签用

OgnlContext类

原理代码演示一

User.java

package com.cx.ognl;/** * Created by cxspace on 16-7-13. */public class User {    private String id;    private String name;    private Address address = new Address("江西省","南昌市");    public Address getAddress() {        return address;    }    public void setAddress(Address address) {        this.address = address;    }    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

测试

    @Test    public void testOgnl() throws OgnlException {        //创建一个ognl对象        OgnlContext context = new OgnlContext();        User user = new User();        user.setId("1");        user.setName("cx");        //设置根元素值        context.setRoot(user);
        //存放一个非根元素        //context.put("user",user);                                          //需要用#号拿值
        //Object ognl = Ognl.parseExpression("#user.name");

        // 底层解析，根元素，不需要加警号        Object ognl = Ognl.parseExpression("name");        //得到value        Object value = Ognl.getValue(ognl,context,context.getRoot());        System.out.println(value);        //context.put("cn","China");        //String value = (String) context.get("cn");        //System.out.println(value);    }

 

 

原理代码演示二

Address.java

package com.cx.ognl;/** * Created by cxspace on 16-7-13. */public class Address {    private String province;    private String city;    public String getProvince() {        return province;    }    public void setProvince(String province) {        this.province = province;    }    public String getCity() {        return city;    }    public void setCity(String city) {        this.city = city;    }    public Address(String province, String city) {        this.province = province;        this.city = city;    }}

    @Test    public void testOngl2() throws OgnlException {        OgnlContext context = new OgnlContext();        User user = new User();        user.setId("122");        user.setName("cxspace");        context.setRoot(user);
        //非根元素
        Object ongl = Ognl.parseExpression("address.province");        Object value = Ognl.getValue(ongl,context,context.getRoot());        System.out.println(value);    }

调用静态方法

    public void testOgnl3() throws Exception{        OgnlContext context = new OgnlContext();        //Ognl调用类的静态方法        Object ognl = Ognl.parseExpression("@Math@floor(10.9)");        //由于math类在开发中常用上面ognl表达式也可以写为@@floor                Object value =  Ognl.getValue(ognl,context,context.getRoot());        System.out.println(value);    }

ValueStack类--值栈

 

是整个Struts数据存储的核心，或者叫中转站。

    每次用户访问struts的action,都会创建一个action对象、值栈对象、ActionContext对象,然后把Action对象放入值栈中，最后把值栈对象放入request中，传入jsp页面。

 

 

开发者只要通过ActionContext对象就可以访问struts的其他的关键对象。

（ActionContext是给开发者用）

 

获取值栈对象的两种方式

 

package com.cx.ognl;import com.opensymphony.xwork2.ActionContext;import com.opensymphony.xwork2.ActionSupport;import com.opensymphony.xwork2.util.ValueStack;import org.apache.struts2.ServletActionContext;import javax.servlet.http.HttpServletRequest;/** * Created by cxspace on 16-7-14. */public class OgnlDemo2 extends ActionSupport {    @Override    public String execute() throws Exception {        //获取值栈对象,方式1        HttpServletRequest request = ServletActionContext.getRequest();        ValueStack vs1 = (ValueStack)request.getAttribute("struts.valueStack");        //获取值栈对象，方式2        ActionContext ac = ActionContext.getContext();        ValueStack vs2 = ac.getValueStack();                System.out.println(vs1==vs2);        //显示true                return SUCCESS;    }}

 

 

ValueStack对象中存储的数据结构图

 

 

 

 

 

值栈对象中的值

 

<br/>1. 取根元素的值<br/>
<s:property value="user.id"/>
<s:property value="user.name"/>
<s:property value="user.address"/>
<s:property value="user.address.city"/>
<s:property value="user.address.province"/>

<br/>2. 取非根元素的值<br/>
<s:property value="#request.cn"/>
<s:property value="#session.Session_data"/>
<s:property value="#application.Application_data"/> <br/>

<!-- 自动找request/session/application,找到后立刻返回 -->
<s:property value="#request_data"/>
<s:property value="#attr.Session_data"/>
<s:property value="#attr.Application_data"/> <br/>

<!-- 获取请求的参数数据 -->
<s:property value="#parameters.userName"/>

<!-- struts的调试标签：可以观测值栈数据 -->
<s:debug></s:debug>

 

OGNL表达式的几个特殊符号

# 非根元素取值、动态构建map集合

$ 配置文件取值

% 提供一个ognl表达式运行环境