【转】关于Filter的若干

filter的执行顺序

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内容如下：

<?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>  
            <span style="color: rgb(255, 0, 0);" mce_style="color: #ff0000;"> <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），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）

出处：http://esteem.javaeye.com/blog/256894

FilterChain 执行过程

下面是一个避免提交数据乱码问题的EncodingFilter:

package anni;  
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 EncodingFilter implements Filter {  
public void init(FilterConfig config) throws ServletException {}  
public void destroy() {}  
public void doFilter(ServletRequest request,  
ServletResponse response,  
FilterChain chain)  
throws IOException, ServletException {  
request.setCharacterEncoding("gb2312");  
chain.doFilter(request, response);  
}  
}  

相应的web.xml为：

<filter>  
<filter-name>EncodingFilter</filter-name>  
<filter-class>anni.EncodingFilter</filter-class>  
</filter>  
<filter-mapping>  
<filter-name>EncodingFilter</filter-name>  
<url-pattern>/*</url-pattern>  
</filter-mapping>

过滤控制访问权限的SecurityFilter:

public void doFilter(ServletRequest request,  
ServletResponse response,  
FilterChain chain)  
throws IOException, ServletException {  
HttpServletRequest req = (HttpServletRequest) request;  
HttpServletResponse res = (HttpServletResponse) response;  
HttpSession session = req.getSession();  
if (session.getAttribute("username") != null) {  
chain.doFilter(request, response);  
} else {  
res.sendRedirect("../failure.jsp");  
}  
}

相应的web.xml为：

<filter>  
<filter-name>SecurityFilter</filter-name>  
<filter-class>anni.SecurityFilter</filter-class>  
</filter>  
<filter-mapping>  
<filter-name>SecurityFilter</filter-name>  
<url-pattern>/admin/*</url-pattern>  
</filter-mapping>

EncodingFilter负责设置编码，SecurityFilter负责控制权限，那这两个过滤器是怎么起作用的呢？它们两个同时过滤一个请求时谁先谁后呢？

所有的奥秘就在Filter中的FilterChain中。服务器会按照web.xml中过滤器定义的先后循序组装成一条链，然后一次执行其中的 doFilter()方法。执行的顺序就如上图所示，执行第一个过滤器的chain.doFilter()之前的代码，第二个过滤器的 chain.doFilter()之前的代码，请求的资源，第二个过滤器的chain.doFilter()之后的代码，第一个过滤器的 chain.doFilter()之后的代码，最后返回响应。

因此在07-02中执行的代码顺序是：

1. 执行EncodingFilter.doFilter()中chain.doFilter()之前的部分：request.setCharacterEncoding("gb2312");

2. 执行SecurityFilter.doFilter()中chain.doFilter()之前的部分：判断用户是否已登录。

   如果用户已登录，则访问请求的资源：/admin/index.jsp。

   如果用户未登录，则页面重定向到：/failure.jsp。

3. 执行SecurityFilter.doFilter()中chain.doFilter()之后的部分：这里没有代码。

4. 执行EncodingFilter.doFilter()中chain.doFilter()之后的部分：这里也没有代码。

过滤链的好处是，执行过程中任何时候都可以打断，只要不执行chain.doFilter()就不会再执行后面的过滤器和请求的内容。而在实际使用时，就要特别注意过滤链的执行顺序问题，像EncodingFilter就一定要放在所有Filter之前，这样才能确保在使用请求中的数据前设置正确的编码。

出处：http://blog.csdn.net/wibnmo/archive/2009/10/22/4714227.aspx