Filter系列五 谈谈启动方面

转自：http://tianhei.iteye.com/blog/970393

Listener、Filter、Servlet都有一个初始化的过程，对应的方法分别为：

contextInitialized(ServletContextEvent arg0)

init(FilterConfig filterConfig)

init(ServletConfig config)

 

那么它们的初始化顺序是什么呢？

Listener > Filter > Servlet

 

TestServlet.java

Java代码  

1. package com.cos;   
2. import java.io.IOException;   
3. import javax.servlet.GenericServlet;   
4. import javax.servlet.ServletConfig;   
5. import javax.servlet.ServletException;   
6. import javax.servlet.ServletRequest;   
7. import javax.servlet.ServletResponse;   
8.   
9. public class TestServlet extends GenericServlet {   
10.     @Override  
11.     public void init(ServletConfig config){   
12.         System.out.println("Servlet 初始化 。。。");   
13.     }   
14.     @Override  
15.     public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {   
16.         System.out.println("Servlet service 。。。");   
17.     }   
18. }  

package com.cos;import java.io.IOException;import javax.servlet.GenericServlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class TestServlet extends GenericServlet {    @Override    public void init(ServletConfig config){        System.out.println("Servlet 初始化 。。。");    }    @Override    public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {        System.out.println("Servlet service 。。。");    }}

 

TestFilter.java

Java代码  

1. package com.cos;   
2. import java.io.IOException;   
3. import javax.servlet.Filter;   
4. import javax.servlet.FilterChain;   
5. import javax.servlet.FilterConfig;   
6. import javax.servlet.ServletException;   
7. import javax.servlet.ServletRequest;   
8. import javax.servlet.ServletResponse;   
9.   
10. public class TestFilter implements Filter{   
11.     public void init(FilterConfig filterConfig) throws ServletException {   
12.         System.out.println("Filter 初始化。。。");   
13.     }   
14.     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {   
15.         System.out.println("doFilter 。。。");   
16.         chain.doFilter(request, response);   
17.     }   
18.     public void destroy() {   
19.         System.out.println("Filter 销毁。。。");   
20.     }   
21. }  

package com.cos;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 TestFilter implements Filter{    public void init(FilterConfig filterConfig) throws ServletException {        System.out.println("Filter 初始化。。。");    }    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {        System.out.println("doFilter 。。。");        chain.doFilter(request, response);    }    public void destroy() {        System.out.println("Filter 销毁。。。");    }}

 

TestListener.java

Java代码  

1. package com.cos;   
2. import javax.servlet.ServletContextEvent;   
3. import javax.servlet.ServletContextListener;   
4.   
5. public class TestListener implements ServletContextListener{   
6.     public void contextInitialized(ServletContextEvent arg0) {   
7.         System.out.println("Listener 初始化。。。");   
8.     }   
9.     public void contextDestroyed(ServletContextEvent arg0) {   
10.         System.out.println("Listener 销毁。。。");   
11.     }   
12. }  

package com.cos;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;public class TestListener implements ServletContextListener{    public void contextInitialized(ServletContextEvent arg0) {        System.out.println("Listener 初始化。。。");    }    public void contextDestroyed(ServletContextEvent arg0) {        System.out.println("Listener 销毁。。。");    }}

 

web.xml

Xml代码  

1. <?xml version="1.0" encoding="UTF-8"?>  
2. <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  
3.     <servlet>  
4.         <servlet-name>s</servlet-name>  
5.         <servlet-class>com.cos.TestServlet</servlet-class>  
6.     </servlet>  
7.     <servlet-mapping>  
8.         <servlet-name>s</servlet-name>  
9.         <url-pattern>/login</url-pattern>  
10.     </servlet-mapping>  
11.     <filter>  
12.         <filter-name>f</filter-name>  
13.         <filter-class>com.cos.TestFilter</filter-class>  
14.     </filter>  
15.     <filter-mapping>  
16.         <filter-name>f</filter-name>  
17.         <url-pattern>/*</url-pattern>  
18.     </filter-mapping>  
19.     <listener>  
20.         <listener-class>com.cos.TestListener</listener-class>  
21.     </listener>  
22. </web-app>  

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">    <servlet>        <servlet-name>s</servlet-name>        <servlet-class>com.cos.TestServlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>s</servlet-name>        <url-pattern>/login</url-pattern>    </servlet-mapping>    <filter>        <filter-name>f</filter-name>        <filter-class>com.cos.TestFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>f</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>    <listener>        <listener-class>com.cos.TestListener</listener-class>    </listener></web-app>

 

启动tomcat后，在控制台里以此打印出：

Listener 初始化。。。

Filter 初始化。。。

信息: Server startup in 675 ms

 

可以看出Listener的初始化最早，Filter次之。他俩的初始化都是在容器启动完成之前初始化的。

Servlet没有初始化，原因是没有匹配的请求进来。

如果想要servlet自动初始化，需要在指定的servlet中配置<load-on-startup>参数，没有此标签，默认启动时servlet不进行初始化。

 

初始化的顺序跟Listener、Filter、Servlet在web.xml中的顺序无关

而多个Filter或多个Servlet的时候，谁的mapping在前面，谁先初始化。

 

如果web.xml中配置了<context-param>，初始化顺序：

context-param > Listener > Filter > Servlet