Servlet中init-param与context-param的区别

时间：2021-02-22 13:23:16

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>

Servlet中init-param与context-param的区别

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




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