读取容器配置参数---context-param和init-param区别

web.xml里面可以定义两种参数：
(1)application范围内的参数，存放在servletcontext中，在web.xml中配置如下：

<context-param>  
           <param-name>context/param</param-name>  
           <param-value>avalible during application</param-value>  
</context-param>  

<context-param>          

<param-name>context/param</param-name>          

<param-value>avalible during application</param-value>

</context-param>

(2)servlet范围内的参数，只能在servlet的init()方法中取得，在web.xml中配置如下：


<servlet>  
    <servlet-name>MainServlet</servlet-name>  
    <servlet-class>com.wes.controller.MainServlet</servlet-class>  
    <init-param>  
       <param-name>param1</param-name>  
       <param-value>avalible in servlet init()</param-value>  
    </init-param>  
    <load-on-startup>0</load-on-startup>  
</servlet>  

<servlet>    

<servlet-name>MainServlet</servlet-name>    

<servlet-class>com.wes.controller.MainServlet</servlet-class>    

<init-param>      

<param-name>param1</param-name>      

<param-value>avalible in servlet init()</param-value>    

</init-param>    

<load-on-startup>0</load-on-startup>

</servlet>

在servlet中可以通过代码分别取用：


package com.wes.controller;   
  
import javax.servlet.ServletException;   
import javax.servlet.http.HttpServlet;   
  
public class MainServlet extends HttpServlet{   
  
    public MainServlet(){   
        super();   
      }   
    public void init() throws ServletException ...{   
          System.out.println("下面的两个参数param1是在servlet中存放的");   
          System.out.println(this.getInitParameter("param1"));   
          System.out.println("下面的参数是存放在servletcontext中的");   
          System.out.println(getServletContext().getInitParameter("context/param"));   
       }   
}  

package com.wes.controller;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

public class MainServlet extends HttpServlet{ 

    public MainServlet(){        

       super();    

}    

public void init() throws ServletException ...{        

System.out.println("下面的两个参数param1是在servlet中存放的");       

System.out.println(this.getInitParameter("param1"));        

System.out.println("下面的参数是存放在servletcontext中的");        

System.out.println(getServletContext().getInitParameter("context/param"));        } }


第一种参数在servlet里面可以通过getServletContext().getInitParameter("context/param")得到

在JSP中可以用config.getServletContext().getInitParameter("context/param")得到

或者this.getServletContext().getInitParameter("context/param")


第二种参数只能在servlet的init()方法中通过this.getInitParameter("param1")取得
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