Listener,Filter,Servlet执行顺序和生命周期

Listener,Filter,Servlet执行顺序和生命周期

Listener,Filter和servlet都是配置在web.xml文件中。

Listener、Filter、Servlet定义：

Listener:

首先定义一个Listener，实现以下接口：

HttpSessionListener(用来监控session的创建，销毁等)

ServletRequestListener(用于监控servlet上下文request)

ServletRequestAttributeListener(用于监控request中的attribute的操作)

package com.xy.web.listener;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TestListener implements HttpSessionListener,ServletRequestListener,ServletRequestAttributeListener {  
    private Logger logger = LoggerFactory.getLogger(TestListener.class);  

    //sessionListener start!  
    public void sessionCreated(HttpSessionEvent arg0) {  
        logger.info(".......TestListener sessionCreated().......");  
    }  

    public void sessionDestroyed(HttpSessionEvent arg0) {  
        logger.info(".......TestListener sessionDestroyed().......");  
    }  
    //sessionListener end!  

    //requestListener start!  
    public void requestInitialized(ServletRequestEvent arg0) {  
        logger.info("......TestListener requestInitialized()......");  
    }  

    public void requestDestroyed(ServletRequestEvent arg0) {  
        logger.info("......TestListener requestDestroyed()......");  
    }  
    //requestListener end!  

    //attributeListener start!  
    public void attributeAdded(ServletRequestAttributeEvent srae) {  
        logger.info("......TestListener attributeAdded()......");  
    }  

    public void attributeRemoved(ServletRequestAttributeEvent srae) {  
        logger.info("......TestListener attributeRemoved()......");  
    }  

    public void attributeReplaced(ServletRequestAttributeEvent srae) {  
        logger.info("......TestListener attributeReplaced()......");  
    }  
    //attributeListener end!   }

Filter：

package com.xy.web.filter; 
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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TestFilter implements Filter {  
    private Logger logger = LoggerFactory.getLogger(TestFilter.class);  

    public void destroy() {  
        logger.info("..............execute TestFilter destory()..............");  
    }  

    public void doFilter(ServletRequest arg0, ServletResponse arg1,FilterChain arg2) throws IOException, ServletException {  
        logger.info("..............execute TestFilter doFilter()..............");  
        arg2.doFilter(arg0, arg1);  
    }  

    public void init(FilterConfig arg0) throws ServletException {  
        logger.info("..............execute TestFilter  init()..............");  
    }
   }

Servlet

package com.xy.web.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.Logger;  import org.slf4j.LoggerFactory;
public class TestServlet extends HttpServlet {  

    private Logger logger = LoggerFactory.getLogger(TestServlet.class);  

    /** 
     *  
     */  
    private static final long serialVersionUID = -4263672728918819141L;  

    @Override  
    public void init() throws ServletException {  
        logger.info("...TestServlet init() init..........");  
        super.init();  
    }  

    @Override  
    public void destroy() {  
        logger.info("...TestServlet init() destory..........");  
        super.destroy();  
    }  
    @Override  
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)  
            throws ServletException, IOException {  
        this.doPost(req, resp);  
    }  

    @Override  
    protected void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        logger.info("...TestServlet doPost() start..........");  
        //操作attribute  
        request.setAttribute("a", "a");  
        request.setAttribute("a", "b");  
        request.getAttribute("a");  
        request.removeAttribute("a");  
        //操作session  
        request.getSession().setAttribute("a", "a");  
        request.getSession().getAttribute("a");  
        request.getSession().invalidate();  
        logger.info("...TestServlet doPost() end..........");  
    }   
}

配置XML：

<!-- 测试filter -->  
<filter>  
    <filter-name>TestFilter</filter-name>  
    <filter-class>com.xy.web.filter.TestFilter</filter-class>  
</filter>  
<filter-mapping>  
    <filter-name>TestFilter</filter-name>  
    <url-pattern>*.do</url-pattern>  
</filter-mapping>  
<!-- 测试servlet -->  
<servlet>  
    <servlet-name>TestServlet</servlet-name>  
    <servlet-class>com.xy.web.servlet.TestServlet</servlet-class>  
</servlet>  
<servlet-mapping>  
    <servlet-name>TestServlet</servlet-name>  
    <url-pattern>/*</url-pattern>  
</servlet-mapping>  
<!-- 测试listener -->  
<listener>  
    <listener-class>com.xy.web.listener.TestListener</listener-class>  
</listener>  

配置好以后启动项目。

加载顺序：
日志：
查看启动日志如下：

信息: Initializing Coyote HTTP/1.1 on http-80

…………

2016-1-14 0:47:04 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextInitialized()
2016-1-14 0:47:04 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextInitialized()

………..

2016-01-14 00:47:23,369 INFO TestFilter:28 - …………..execute TestFilter init()…………..
2016-1-14 0:47:23 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet ‘spring’
………..

2016-1-14 0:47:25 org.apache.catalina.startup.Catalina start
信息: Server startup in 21565 ms

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结论：

从启动日志来看，

启动的顺序为listener->Filter->servlet.

简单记为：理(Listener)发(Filter)师(servlet).

执行的顺序不会因为三个标签在配置文件中的先后顺序而改变。

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生命周期：
日志：
访问项目路径：http://localhost/MyWebProject/common/test.do，访问action两次，打断点后查看日志情况：
第一次访问：

2016-01-14 00:03:03,991 INFO TestListener:26 - ……TestListener requestInitialized()……
2016-01-14 00:03:04,001 INFO TestServlet:24 - …TestServlet init() init……….
2016-01-14 00:03:04,011 INFO TestFilter:23 - …………..execute TestFilter doFilter()…………..
2016-01-14 00:03:15,275 INFO TestServlet:42 - …TestServlet doPost() start……….
2016-01-14 00:03:16,255 INFO TestListener:36 - ……TestListener attributeAdded()……
2016-01-14 00:03:16,853 INFO TestListener:44 - ……TestListener attributeReplaced()……
2016-01-14 00:03:18,561 INFO TestListener:40 - ……TestListener attributeRemoved()……
2016-01-14 00:03:20,065 INFO TestListener:16 - …….TestListener sessionCreated()…….
2016-01-14 00:03:22,908 INFO TestListener:20 - …….TestListener sessionDestroyed()…….
2016-01-14 00:03:25,624 INFO TestServlet:52 - …TestServlet doPost() end……….
2016-01-14 00:03:27,746 INFO TestListener:30 - ……TestListener requestDestroyed()……

第二次访问：

2016-01-14 00:04:08,908 INFO TestListener:26 - ……TestListener requestInitialized()……
2016-01-14 00:04:08,909 INFO TestFilter:23 - …………..execute TestFilter doFilter()…………..
2016-01-14 00:04:14,385 INFO TestServlet:42 - …TestServlet doPost() start……….
2016-01-14 00:04:14,778 INFO TestListener:36 - ……TestListener attributeAdded()……
2016-01-14 00:04:14,974 INFO TestListener:44 - ……TestListener attributeReplaced()……
2016-01-14 00:04:15,342 INFO TestListener:40 - ……TestListener attributeRemoved()……
2016-01-14 00:04:15,904 INFO TestListener:16 - …….TestListener sessionCreated()…….
2016-01-14 00:04:17,354 INFO TestListener:20 - …….TestListener sessionDestroyed()…….
2016-01-14 00:04:17,815 INFO TestServlet:52 - …TestServlet doPost() end……….
2016-01-14 00:04:19,044 INFO TestListener:30 - ……TestListener requestDestroyed()……

关闭项目，打印日志如下：

2016-1-14 0:40:15 org.apache.coyote.http11.Http11Protocol pause
信息: Pausing Coyote HTTP/1.1 on http-80
2016-1-14 0:40:16 org.apache.catalina.core.StandardService stop
信息: Stopping service Catalina
2016-1-14 0:40:16 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextDestroyed()
2016-1-14 0:40:16 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextDestroyed()
2016-01-14 00:40:16,561 INFO TestServlet:30 - …TestServlet init() destory……….
…….
2016-01-14 00:40:22,091 INFO TestFilter:19 - …………..execute TestFilter destroy()…………..

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结论：
从启动，结束和运行时候的日志看：

Listener生命周期：一直从程序启动到程序停止运行。

ServletRequestListener：每次访问一个Request资源前，都会执行requestInitialized()方法，方法访问完毕，都会执行requestDestroyed()方法。

HttpSessionListener：每次调用request.getSession()，都会执行sessionCreated()方法，执行session.invalidate()方法，都会执行sessionDestroyed()方法。

ServletRequestAttributeListener：每次调用request.setAttribute()都会执行attributeAdded()方法，如果set的key在request里面存在，就会执行attributeReplacerd()方法，调用request.removeAttribute()方法，都会执行attributeRemoved()方法。

Filter生命周期：程序启动调用Filter的init()方法(永远只调用一次,具体看启动日志)，程序停止调用Filter的destroy()方法(永远只调用一次，具体看关闭日志)，doFilter()方法每次的访问请求如果符合拦截条件都会调用(程序第一次运行，会在servlet调用init()方法以后调用，不管第几次，都在调用doGet(),doPost()方法之前)。

Servlet生命周期：程序第一次访问，会调用servlet的init()方法初始化(只执行一次，具体看日志)，每次程序执行都会根据请求调用doGet()或者doPost()方法，程序停止调用destory()方法(具体看结束日志)。

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