Servlet、Filter 和 Listener 调用顺序、生命周期的实验分析

Servlet、Filter 和 Listener 调用顺序、生命周期的实验分析

博客分类：
• JAVA

 

通过实验来验证Servlet、Filter和Listener的调用顺序、生命周期。

1、示例项目

目录结构：

web.xml

Java代码  

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">  
3. <web-app>  
4.     <listener>  
5.         <listener-class>edu.shao.webapp.sample.listener.MyServletRequestListener</listener-class>  
6.     </listener>  
7.     <listener>  
8.         <listener-class>edu.shao.webapp.sample.listener.MyServletContextListener</listener-class>  
9.     </listener>  
10.       
11.     <filter>  
12.         <filter-name>ResponseFilter</filter-name>  
13.         <filter-class>edu.shao.webapp.sample.filter.ResponseFilter</filter-class>  
14.     </filter>  
15.     <filter-mapping>  
16.         <filter-name>ResponseFilter</filter-name>  
17.         <servlet-name>hello_world</servlet-name>  
18.     </filter-mapping>  
19.       
20.     <filter>  
21.         <filter-name>LogFilter</filter-name>  
22.         <filter-class>edu.shao.webapp.sample.filter.LogFilter</filter-class>  
23.     </filter>  
24.     <filter-mapping>  
25.         <filter-name>LogFilter</filter-name>  
26.         <url-pattern>/*</url-pattern>  
27.     </filter-mapping>  
28.       
29.     <servlet>  
30.         <servlet-name>hello_world</servlet-name>  
31.         <servlet-class>edu.shao.webapp.sample.HelloServlet</servlet-class>  
32.     </servlet>  
33.     <servlet-mapping>  
34.         <servlet-name>hello_world</servlet-name>  
35.         <url-pattern>/hello</url-pattern>  
36.     </servlet-mapping>  
37.       
38.     <servlet>  
39.         <servlet-name>early_servlet</servlet-name>  
40.         <servlet-class>edu.shao.webapp.sample.EarlyServlet</servlet-class>  
41.         <load-on-startup>1</load-on-startup>  
42.     </servlet>  
43.     <servlet-mapping>  
44.         <servlet-name>early_servlet</servlet-name>  
45.         <url-pattern>/early</url-pattern>  
46.     </servlet-mapping>  
47. </web-app>  

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd"><web-app>    <listener>        <listener-class>edu.shao.webapp.sample.listener.MyServletRequestListener</listener-class>    </listener>    <listener>        <listener-class>edu.shao.webapp.sample.listener.MyServletContextListener</listener-class>    </listener>        <filter>        <filter-name>ResponseFilter</filter-name>        <filter-class>edu.shao.webapp.sample.filter.ResponseFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>ResponseFilter</filter-name>        <servlet-name>hello_world</servlet-name>    </filter-mapping>        <filter>        <filter-name>LogFilter</filter-name>        <filter-class>edu.shao.webapp.sample.filter.LogFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>LogFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>        <servlet>        <servlet-name>hello_world</servlet-name>        <servlet-class>edu.shao.webapp.sample.HelloServlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>hello_world</servlet-name>        <url-pattern>/hello</url-pattern>    </servlet-mapping>        <servlet>        <servlet-name>early_servlet</servlet-name>        <servlet-class>edu.shao.webapp.sample.EarlyServlet</servlet-class>        <load-on-startup>1</load-on-startup>    </servlet>    <servlet-mapping>        <servlet-name>early_servlet</servlet-name>        <url-pattern>/early</url-pattern>    </servlet-mapping></web-app>

MyServletContextListener类：

Java代码  

1. public class MyServletContextListener implements ServletContextListener {  
2.     public static Logger logger=LogManager.getLogger(MyServletContextListener.class);  
3.   
4.     @Override  
5.     public void contextInitialized(ServletContextEvent sce) {  
6.         logger.info("Servlet context initialized.");  
7.     }  
8.   
9.     @Override  
10.     public void contextDestroyed(ServletContextEvent sce) {  
11.         logger.info("Servlet context destroyed.");  
12.     }  
13. }  

public class MyServletContextListener implements ServletContextListener {    public static Logger logger=LogManager.getLogger(MyServletContextListener.class);    @Override    public void contextInitialized(ServletContextEvent sce) {        logger.info("Servlet context initialized.");    }    @Override    public void contextDestroyed(ServletContextEvent sce) {        logger.info("Servlet context destroyed.");    }}

MyServletRequestListener类：

Java代码  

1. public class MyServletRequestListener implements ServletRequestListener {  
2.     public static Logger logger=LogManager.getLogger(MyServletRequestListener.class);  
3.   
4.     @Override  
5.     public void requestDestroyed(ServletRequestEvent sre) {  
6.         logger.info("Servlet request destroyed.");  
7.     }  
8.   
9.     @Override  
10.     public void requestInitialized(ServletRequestEvent sre) {  
11.         logger.info("Servlet request initialized.");  
12.     }  
13. }  

public class MyServletRequestListener implements ServletRequestListener {    public static Logger logger=LogManager.getLogger(MyServletRequestListener.class);    @Override    public void requestDestroyed(ServletRequestEvent sre) {        logger.info("Servlet request destroyed.");    }    @Override    public void requestInitialized(ServletRequestEvent sre) {        logger.info("Servlet request initialized.");    }}

ResponseFilter类：

Java代码  

1. public class ResponseFilter implements Filter {  
2.     public static Logger logger=LogManager.getLogger(ResponseFilter.class);  
3.       
4.     @Override  
5.     public void init(FilterConfig arg0) throws ServletException {  
6.         logger.info("Response Filter initialized.");  
7.     }  
8.   
9.     @Override  
10.     public void doFilter(ServletRequest req, ServletResponse res,  
11.             FilterChain chain) throws IOException, ServletException {  
12.         chain.doFilter(req, res);  
13.         res.getWriter().write("--@2013 Mr.Shao");  
14.     }  
15.   
16.     @Override  
17.     public void destroy() {  
18.         logger.info("Response Filter destroyed.");  
19.     }  
20. }  

public class ResponseFilter implements Filter {    public static Logger logger=LogManager.getLogger(ResponseFilter.class);        @Override    public void init(FilterConfig arg0) throws ServletException {        logger.info("Response Filter initialized.");    }    @Override    public void doFilter(ServletRequest req, ServletResponse res,            FilterChain chain) throws IOException, ServletException {        chain.doFilter(req, res);        res.getWriter().write("--@2013 Mr.Shao");    }    @Override    public void destroy() {        logger.info("Response Filter destroyed.");    }}

LogFilter类：

Java代码  

1. public class LogFilter implements Filter {  
2.     public static Logger logger=LogManager.getLogger(LogFilter.class);  
3.       
4.     @Override  
5.     public void init(FilterConfig filterConfig) throws ServletException {  
6.         logger.info("Log Filter initialized.");  
7.     }  
8.   
9.     @Override  
10.     public void doFilter(ServletRequest request, ServletResponse response,  
11.             FilterChain chain) throws IOException, ServletException {  
12.         HttpServletRequest httpServletRequest = (HttpServletRequest)request;  
13.         logger.info("Intercept Url="+httpServletRequest.getRequestURI());  
14.           
15.         long start=System.currentTimeMillis();  
16.         chain.doFilter(request, response);  
17.         long end=System.currentTimeMillis();  
18.         logger.info(request.getRemoteAddr()+": time used :"+(end-start));  
19.     }  
20.   
21.     @Override  
22.     public void destroy() {  
23.         logger.info("Log Filter destroyed.");  
24.     }  
25. }  

public class LogFilter implements Filter {    public static Logger logger=LogManager.getLogger(LogFilter.class);        @Override    public void init(FilterConfig filterConfig) throws ServletException {        logger.info("Log Filter initialized.");    }    @Override    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        HttpServletRequest httpServletRequest = (HttpServletRequest)request;        logger.info("Intercept Url="+httpServletRequest.getRequestURI());                long start=System.currentTimeMillis();        chain.doFilter(request, response);        long end=System.currentTimeMillis();        logger.info(request.getRemoteAddr()+": time used :"+(end-start));    }    @Override    public void destroy() {        logger.info("Log Filter destroyed.");    }}

HelloServlet类：

Java代码  

1. public class HelloServlet extends HttpServlet {  
2.     public static Logger logger=LogManager.getLogger(HelloServlet.class);  
3.   
4.     @Override  
5.     public void doGet(HttpServletRequest req, HttpServletResponse resp)  
6.             throws ServletException, IOException {  
7.         logger.debug("Do Get Method.");  
8.         resp.getWriter().print("Hello World");  
9.     }  
10.       
11.     public void init() throws ServletException {  
12.         logger.debug("Hello Servlet initialized.");  
13.     }  
14.       
15.     public void destroy() {  
16.         logger.debug("Hello Servlet destroyed.");  
17.     }  
18. }  

public class HelloServlet extends HttpServlet {    public static Logger logger=LogManager.getLogger(HelloServlet.class);    @Override    public void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        logger.debug("Do Get Method.");        resp.getWriter().print("Hello World");    }        public void init() throws ServletException {        logger.debug("Hello Servlet initialized.");    }        public void destroy() {        logger.debug("Hello Servlet destroyed.");    }}

EarlyServlet类：

Java代码  

1. public class EarlyServlet extends HttpServlet {  
2.     public static Logger logger=LogManager.getLogger(EarlyServlet.class);  
3.   
4.     @Override  
5.     public void doGet(HttpServletRequest req, HttpServletResponse resp)  
6.             throws ServletException, IOException {  
7.         logger.debug("Do Get Method.");  
8.         resp.getWriter().print("This message is created in EarlyServlet");  
9.     }  
10.       
11.     public void init() throws ServletException {  
12.         logger.debug("Early Servlet initialized.");  
13.     }  
14.       
15.     public void destroy() {  
16.         logger.debug("Early Servlet destroyed.");  
17.     }  
18. }  

public class EarlyServlet extends HttpServlet {    public static Logger logger=LogManager.getLogger(EarlyServlet.class);    @Override    public void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        logger.debug("Do Get Method.");        resp.getWriter().print("This message is created in EarlyServlet");    }        public void init() throws ServletException {        logger.debug("Early Servlet initialized.");    }        public void destroy() {        logger.debug("Early Servlet destroyed.");    }}

2、测试操作
1、启动tomcat服务
2、访问http://10.130.29.198:8080/test/  （访问index.html）
3、访问http://10.130.29.198:8080/test/hello
4、访问http://10.130.29.198:8080/test/early
5、停止tomcat服务

3、Log输出

(根据输出的时间，人为的把日志分割开来，便于观察)
1、启动tomcat服务
2013-03-28 18:14:08,954 INFO  - [MyServletContextListener - contextInitialized] Servlet context initialized.
2013-03-28 18:14:08,983 INFO  - [LogFilter - init] Log Filter initialized.
2013-03-28 18:14:08,984 INFO  - [ResponseFilter - init] Response Filter initialized.
2013-03-28 18:14:08,991 DEBUG - [EarlyServlet - init] Early Servlet initialized.
2、访问http://10.130.29.198:8080/test/  （访问index.html）
2013-03-28 18:14:18,946 INFO  - [MyServletRequestListener - requestInitialized] Servlet request initialized.
2013-03-28 18:14:18,957 INFO  - [LogFilter - doFilter] Intercept Url=/test/
2013-03-28 18:14:18,962 INFO  - [LogFilter - doFilter] 10.130.29.198: time used :4
2013-03-28 18:14:18,963 INFO  - [MyServletRequestListener - requestDestroyed] Servlet request destroyed.
3、访问http://10.130.29.198:8080/test/hello
2013-03-28 18:14:34,713 INFO  - [MyServletRequestListener - requestInitialized] Servlet request initialized.
2013-03-28 18:14:34,714 DEBUG - [HelloServlet - init] Hello Servlet initialized.
2013-03-28 18:14:34,716 INFO  - [LogFilter - doFilter] Intercept Url=/test/hello
2013-03-28 18:14:34,717 DEBUG - [HelloServlet - doGet] Do Get Method.
2013-03-28 18:14:34,720 INFO  - [LogFilter - doFilter] 10.130.29.198: time used :3
2013-03-28 18:14:34,721 INFO  - [MyServletRequestListener - requestDestroyed] Servlet request destroyed.
4、访问http://10.130.29.198:8080/test/early
2013-03-28 18:14:42,124 INFO  - [MyServletRequestListener - requestInitialized] Servlet request initialized.
2013-03-28 18:14:42,127 INFO  - [LogFilter - doFilter] Intercept Url=/test/early
2013-03-28 18:14:42,128 DEBUG - [EarlyServlet - doGet] Do Get Method.
2013-03-28 18:14:42,129 INFO  - [LogFilter - doFilter] 10.130.29.198: time used :1
2013-03-28 18:14:42,130 INFO  - [MyServletRequestListener - requestDestroyed] Servlet request destroyed.
5、停止tomcat服务
2013-03-28 18:14:49,723 DEBUG - [EarlyServlet - destroy] Early Servlet destroyed.
2013-03-28 18:14:49,724 DEBUG - [HelloServlet - destroy] Hello Servlet destroyed.
2013-03-28 18:14:49,724 INFO  - [LogFilter - destroy] Log Filter destroyed.
2013-03-28 18:14:49,726 INFO  - [ResponseFilter - destroy] Response Filter destroyed.
2013-03-28 18:14:49,727 INFO  - [MyServletContextListener - contextDestroyed] Servlet context destroyed.

4、分析

1、在Tomcat（Servlet容器）启动时，Listener和 ServletContext 最先初始化。因为最先输出的日志是：
　　2013-03-28 18:14:08,954 INFO - [MyServletContextListener - contextInitialized] Servlet context initialized.
2、Filter在Tomcat（Servlet容器）启动时初始化。
　　2013-03-28 18:14:08,983 INFO - [LogFilter - init] Log Filter initialized.
　　2013-03-28 18:14:08,984 INFO - [ResponseFilter - init] Response Filter initialized.
3、如果某个Servlet配置了 <load-on-startup >1 </load-on-startup >，该Servlet也是在Tomcat（Servlet容器）启动时初始化。例如 EarlyServlet：
　　2013-03-28 18:14:08,991 DEBUG - [EarlyServlet - init] Early Servlet initialized.
4、每次请求， Request都会被初始化，响应请求后，请求被销毁：
　　2013-03-28 18:14:18,946 INFO - [MyServletRequestListener - requestInitialized] Servlet request initialized.
　　......
　　2013-03-28 18:14:18,963 INFO - [MyServletRequestListener - requestDestroyed] Servlet request destroyed.
5、Filter在请求执行前后，都能做一些处理。
　　（1）请求执行前：2013-03-28 18:14:34,716 INFO - [LogFilter - doFilter] Intercept Url=/test/hello
　　（2）执行请求：2013-03-28 18:14:34,717 DEBUG - [HelloServlet - doGet] Do Get Method.
　　（3）请求执行后：2013-03-28 18:14:34,720 INFO - [LogFilter - doFilter] 10.130.29.198: time used :3
6、如果Servlet没有配置<load-on-startup >1 </load-on-startup >，该Servlet不会在Tomcat启动时初始化，而是在请求到来时初始化。例如 HelloServlet：
　　2013-03-28 18:14:34,714 DEBUG - [HelloServlet - init] Hello Servlet initialized.
7、Servlet初始化后，将不会随着请求的结束而注销。HelloServlet 初始化，当请求结束了，HelloServlet 的 destroy() 没有被调用。
8、关闭Tomcat时，Servlet、Filter、Listener依次被注销。

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