web三大组件的加载顺序

Web三大组件：过滤器组件  监听器组件  Servlet组件

过滤器的顶级接口:javax.servlet.Filter

监听器的顶级接口:javax.servlet.ServletContextListener

Servlet的顶级接口:javax.servlet.Servlet

测试如下:

MyServlet:

package web;import java.io.IOException;import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class MyServlet implements Servlet {
    public void destroy() {
        System.out.println("Servelt销毁了");
    }
    public ServletConfig getServletConfig() {
        return null;
    }
    public String getServletInfo() {
        return null;
    }
    public void init(ServletConfig arg0) throws ServletException {
        System.out.println("Servelt加载了");
    }
    public void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException {    }
}

MyFilter：

package web;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class MyFilter implements Filter {
    public void destroy() {
        System.out.println("Filter销毁了");
    }    public void doFilter(ServletRequest arg0, ServletResponse arg1,
            FilterChain arg2) throws IOException, ServletException {    }    public void init(FilterConfig config) throws ServletException {
        System.out.println("Filter加载了");
    }
}

MyListener：

package web;import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;public class MyListener implements ServletContextListener {    public void contextDestroyed(ServletContextEvent arg0) {
        System.out.println("Listener销毁了");
    }    public void contextInitialized(ServletContextEvent arg0) {
            System.out.println("Listener加载了");
    }}

接着需要在web.xml文件中配置这些组件，注意看web.xml文件中的配置顺序:

web.xml文件:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
  <display-name>loadOrder</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <!-- 过滤器-->
  <filter>
    <display-name>MyFilter</display-name>
    <filter-name>MyFilter</filter-name>
    <filter-class>web.MyFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>MyFilter</filter-name>
    <url-pattern>/MyFilter</url-pattern>
  </filter-mapping>    <!-- Servlet组件 -->
  <servlet>
    <description></description>
    <display-name>MyServlet</display-name>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>web.MyServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>  <!-- 监听器 -->
  <listener>
    <listener-class>web.MyListener</listener-class>
  </listener></web-app>

按照如上配置之后:

当启动服务器后其结果为:

Listener加载了

Filter加载了

Servelt加载了

总结:所以三大组件的加载顺序与配置文件的顺序无关,其加载顺序为：Listener>Filter>Servlet