一直没有仔细去研究下filter ，最近系统的测试了下：

先看代码吧

FirstFilter.java
==================
package com.test.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;

public class FirstFilter implements Filter {

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("before invoke firstFilter's chain.doFilter() ..");
        chain.doFilter(request, response);
        System.out.println("after invoke firstFilter's chain.doFilter() ..");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        System.out.println("firstFilter init()...");

    }

}


============

SecondFilter.java
==============

package com.test.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;

public class SecondFilter implements Filter {

    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("before invoke secondFilter's chain.doFilter() ..");
        chain.doFilter(request, response);
        System.out.println("after invoke secondFilter's chain.doFilter() ..");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("secondFilter init()...");
    }

}
==========

FirstServlet.java
=============
package com.test.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("servlet doGet be invoked...");
        req.getRequestDispatcher("test.jsp").forward(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(req, resp);
    }

}

=========

web.xml

===========
<?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">
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <filter>
        <filter-name>firstFilter</filter-name>
        <filter-class>com.test.filter.FirstFilter</filter-class>
    </filter>
    <filter>
        <filter-name>secondFilter</filter-name>
        <filter-class>com.test.filter.SecondFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>secondFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>firstFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <servlet>
        <servlet-name>firstServlet</servlet-name>
        <servlet-class>com.alimama.servlet.FirstServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>firstServlet</servlet-name>
        <url-pattern>/firstServlet</url-pattern>
    </servlet-mapping>
</web-app>

============

 然后发布，发现打印的日志如下：

。。。

firstFilter init()...

secondFilter init()...

。。。

2008-10-23 11:36:43 org.apache.catalina.startup.Catalina start

信息: Server startup in 3665 ms

 

这里过滤器初始化好了。

当我们访问我们的 应用：

发现打印日记如下：

before invoke secondFilter's chain.doFilter() ..

before invoke firstFilter's chain.doFilter() ..

after invoke firstFilter's chain.doFilter() ..

after invoke secondFilter's chain.doFilter() ..

 

当我们将web.xml中filter的位置进行调整后：

<?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">
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <filter>
        <filter-name>firstFilter</filter-name>
        <filter-class>com.test.filter.FirstFilter</filter-class>
    </filter>
    <filter>
        <filter-name>secondFilter</filter-name>
        <filter-class>com.test.filter.SecondFilter</filter-class>
    </filter>
   <filter-mapping>
        <filter-name>firstFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>secondFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping></span>

    <servlet>
        <servlet-name>firstServlet</servlet-name>
        <servlet-class>com.alimama.servlet.FirstServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>firstServlet</servlet-name>
        <url-pattern>/firstServlet</url-pattern>
    </servlet-mapping>
</web-app>

  然后在启动应用，会看到打印：

before invoke firstFilter's chain.doFilter() ..

before invoke secondFilter's chain.doFilter() ..

after invoke secondFilter's chain.doFilter() ..

after invoke firstFilter's chain.doFilter() ..

总结：

filter的执行顺序是按照web.xml中定义的顺序进行执行的（当多个filter都匹配的时候）。