Servlet中init-param与context-param的区别

web.xml文件中Servlet中配置如下:

<servlet>

    <servlet-name>loginServlet</servlet-name>

    <servlet-class>com.qcc.study.servlet02.LoginServlet</servlet-class>

    <!-- 配置Servlet初始化参数 -->

    <init-param>

        <param-name>initParam</param-name>

        <param-value>qcc</param-value>

    </init-param>

    <!-- Web容器启动时就加载并实例化该Servlet -->

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

</servlet>

<servlet-mapping>

    <servlet-name>loginServlet</servlet-name>

    <url-pattern>/login</url-pattern>

</servlet-mapping>

<!-- 配置ContextParam全局参数 -->

<context-param>

    <param-name>contextParam</param-name>

    <param-value>admin</param-value>

</context-param>

使用示例如下:

有login.jsp页面,代码如下:

<%@ 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="login" method="post">

        user:<input type="text" name="username" /><br/>

        password:<input type="password" name="password" /><br/>

        <input type="submit" value="Submit" />

    </form>

</body>

</html>

当访问该jsp页面,并点击表单的提交按钮时,会将表单数据发送到login这个地址,这个login对应定义的serlvet的<url-mapping>的入口文件,请求被LoginServlet的doPost()方法处理,

LoginServlet的源码如下:

package com.qcc.study.servlet02;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException {

        //获取servlet初始化参数:

        String initParam = getServletConfig().getInitParameter("initParam");

        System.out.println("initParam: ---->" + initParam);

        //获取全局初始化参数:

        String contextParam = getServletContext().getInitParameter("contextParam");

        System.out.println("contextParam: ---->" + contextParam);

        //获取用户提交过来的数据:

        String username = req.getParameter("username");

        String password = req.getParameter("password");

        System.out.println("用户提交的数据:" + username + " , " + password);

    }

}

二者的区别:
<init-parm>配置在<servlet>标签中,用来初始化当前的Servlet的,属于当前Servlet的配置,因此存放在servletConfig对象中;

通过getServletConfig().getInitParameter("initParam")的方式获取;

<context-param>直接配置在web.xml的<web-app>标签中,属于上下文参数,在整个web应用中都可以使用,它是全局的,因此存放在servletContext对象中(即application对象);

通过getServletContext().getInitParameter("contextParam")的方式获取;

打印结果:

initParam: ---->qcc

contextParam: ---->admin

用户提交的数据:admin , 123

WEB

Servlet中init-param与context-param的区别