結論:

1.jsp中用EL表示式（${attribute_name}）的讀取順序：model > session > application > requset

2.慎重使用session變數,這個範圍太大了,如果因為一個模組把變數存在session中實現起來更容易,就這樣做了,那麼這就很容易為後面埋下bug.

測試程式碼：

controller類：

package com.my.innerParam.test;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * 測試幾個內建變數中在EL讀取的順序
 * @author rocky
 *
 */
@Controller
public class InnerParam
{
    @RequestMapping("/innerParamTest")
    public String innerParamTest(HttpServletRequest request,HttpServletResponse response,Model model)
    {
        HttpSession session = request.getSession();
        session.setAttribute("session", "session223");
        
        ServletContext application = request.getServletContext();
       // application.setInitParameter("appicationParam", "appicationParam");
        //Initialization parameters can not be set after the context has been initialized
        application.setAttribute("appicationAttr", "applicationAttr");
        request.setAttribute("request", "request");
       
        
        model.addAttribute("model", "model123");
        return "/testParam/testParam1";
    }
    
    //當變數名字相同時判斷EL表示式用哪一個
    @RequestMapping("/innerParamTest2")
    public String innerParamTest2(HttpServletRequest request,HttpServletResponse response,Model model)
    {
        HttpSession session = request.getSession();
        session.setAttribute("test", "session223");
        
        ServletContext application = request.getServletContext();
       // application.setInitParameter("appicationParam", "appicationParam");
        //Initialization parameters can not be set after the context has been initialized
        application.setAttribute("test", "applicationAttr");
  
        request.setAttribute("test", "request");
        model.addAttribute("test", "model123");
        return "/testParam/testParam2";
    }
    
    //當model是null的時候
    @RequestMapping("/innerParamTest3")
    public String innerParamTest3(HttpServletRequest request,HttpServletResponse response,Model model)
    {
        HttpSession session = request.getSession();
        session.setAttribute("test", "session223");
        
        ServletContext application = request.getServletContext();
       // application.setInitParameter("appicationParam", "appicationParam");
        //Initialization parameters can not be set after the context has been initialized
        application.setAttribute("test", "applicationAttr");
  
        request.setAttribute("test", "request");
        model.addAttribute("test", null);
        return "/testParam/testParam3";
    }
}
 

jsp頁面：

1、顯示

<h3>session : ${session}</h3>
<h3>appicationAttr : '${appicationAttr}'</h3>
<h3>appicationParam : '${appicationParam}'</h3>
<h3>request : '${request}'</h3>
<h3>model : '${model}'</h3>

執行結果
session : session223

appicationAttr : 'applicationAttr'

appicationParam : ''

request : 'request'

model : 'model123'
 

<h3>session : ${test}</h3>
<h3>appicationAttr : '${test}'</h3>
<h3>appicationParam : '${test}'</h3>
<h3>request : '${test}'</h3>
<h3>model : '${test}'</h3>

執行結果
session : model123

appicationAttr : 'model123'

appicationParam : 'model123'

request : 'model123'

model : 'model123'