context-param和init-param区别

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web.xml文件中Servlet中配置如下:

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<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>

    <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:

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<%@ 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>

<%@ 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:

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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);
}
}

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:

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initParam: —->qcc
contextParam: —->admin
用户提交的数据:admin , 123

initParam: ---->qcccontextParam: ---->admin用户提交的数据:admin , 123

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