struts2与Servlet API解耦

与Servlet API解耦的访问方式

　　为了避免与 Servlet API 耦合在一起, 方便 Action 做单元测试, Struts2 对 HttpServletRequest, HttpSession 和 ServletContext 进行了封装, 构造了 3 个 Map 对象来替代这 3 个对象, 在 Action 中可以直接使用 HttpServletRequest, HttpSession, ServletContext 对应的 Map 对象来保存和读取数据. 

访问request/session/application对象

　　方法一:通过ServletActionContext类直接获取

　　　　ActionContext 是 Action 执行的上下文对象, 在 ActionContext 中保存了 Action 执行所需要的所有对象, 包括 parameters, request, session, application 等. 

　　　　a) 获取 HttpServletRequest 对应的 Map 对象

　　　　　　•public Object get(Object key): ActionContext 类中没有提供类似 getRequest() 这样的方法来获取 HttpServletRequest 对应的 Map 对象.

　　　　　　 要得到 HttpServletRequest 对应的 Map 对象, 可以通过为 get() 方法传递 “request” 参数实现

　　　　b) 获取 HttpSession 对应的 Map 对象: 

　　　　　　•public Map getSession()

　　　　c) 获取 ServletContext 对应的 Map 对象:

　　　　　　•public Map getApplication()

import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionSupport;

@SuppressWarnings("serial")
public class ContextAction extends ActionSupport {

    public String test(){
        System.out.println("ContextAction*********test()");
        
        HttpServletRequest request = ServletActionContext.getRequest();
        request.setAttribute("username", "username_request");
        HttpServletResponse response = ServletActionContext.getResponse();
        
        Map  sessionMap = ServletActionContext.getContext().getSession();
        sessionMap.put("username","username_session");
        
        ServletContext  sc =  ServletActionContext.getServletContext();
        sc.setAttribute("username","username_context");
        
        return "attr";
    }
}

　　　　如果你只是想访问session的属性（Attribute），你也可以通过ActionContext.getContext().getSession()获取

　　方法二:实现指定接口，由struts框架运行时注入：

　　Action 类通过可以实现某些特定的接口, 让Struts2 框架在运行时向 Action 实例注入parameters, request, session 和 application 对应的 Map 对象: 

　　

import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts2.ServletActionContext;
import org.apache.struts2.interceptor.ServletRequestAware;
import org.apache.struts2.interceptor.ServletResponseAware;
import org.apache.struts2.interceptor.SessionAware;
import org.apache.struts2.util.ServletContextAware;

import com.opensymphony.xwork2.ActionSupport;

@SuppressWarnings("serial")
public class ContextAction2 extends ActionSupport implements ServletRequestAware,ServletResponseAware,ServletContextAware,SessionAware{

    HttpServletRequest request;
    HttpServletResponse response;
    Map  sessionMap;
    ServletContext  sc;
    
    public String test(){
        System.out.println("ContextAction*********test()");
        HttpServletRequest request = ServletActionContext.getRequest();
        request.setAttribute("username", "username_request");
        sessionMap.put("username","username_session");
        sc.setAttribute("username","username_context");
        return "attr";
    }
    @Override
    public void setSession(Map<String, Object> session) {
        this.sessionMap =session;
    }
    @Override
    public void setServletContext(ServletContext context) {
        this.sc = context;
    }
    @Override
    public void setServletResponse(HttpServletResponse response) {
        this.response = response;
    }
    @Override
    public void setServletRequest(HttpServletRequest request) {
        
    }
}

　　struts_context.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="context" namespace="/context"  extends="struts-default"> 
         <action name="contextAction_test" class="cn.zengfansheng.struts.context.ContextAction" method="test">
            <result name="success">
                <param name="location">/context/success.jsp</param>
            </result>
            <result name="attr">/context/attr.jsp</result>
         </action>
         <action name="contextAction2_test" class="cn.zengfansheng.struts.context.ContextAction2" method="test">
            <result name="success">
                <param name="location">/context/success.jsp</param>
            </result>
            <result name="attr">/context/attr.jsp</result>
         </action>
    </package>
</struts>

　　attr.sjp

<%@ page language="java" pageEncoding="utf-8"%>
<%@ taglib uri="/struts-tags"   prefix="s"%>
<html>
  <head>
    <title>My JSP 'index.jsp' starting page</title>
    <meta http-equiv="description" content="This is my page">
  </head>
  <body>
    ${requestScope.username}<br>
    ${sessionScope.username}<br>
    ${applicationScope.username}<br>
  </body>
</html>