filter的执行顺序

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J2EE

Servlet JavaEE Web XML SUN

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：http://127.0.0.1:8080/appName

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>
	
	<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），执行顺序如下图表示。（PS图取自http://hi.baidu.com/cathy_200182/blog/item/1f686238df10eb22b8998fe3.html 感谢之）