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

程序员文章站 2022-06-23 18:37:01

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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

<?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：

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：

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：

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("[email protected] Mr.Shao");
    }

    @Override
    public void destroy() {
        logger.info("Response Filter destroyed.");
    }
}

LogFilter类：

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：

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：

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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