servlet过滤器的链式处理

分类： Java

先贴代码，用输出结果来阐述原理。

[java] view plaincopyprint?

1. package org.lxh.filterdemo;  
2.   
3. import java.io.IOException;  
4. import javax.servlet.Filter;  
5. import javax.servlet.FilterChain;  
6. import javax.servlet.FilterConfig;  
7. import javax.servlet.ServletException;  
8. import javax.servlet.ServletRequest;  
9. import javax.servlet.ServletResponse;  
10.   
11. public class SimpleFilter implements Filter{  
12.     public void init(FilterConfig config) throws ServletException{  
13.         String initParam = config.getInitParameter("ref");  
14.         System.out.println("** 过滤器初始化，初始化参数="+initParam+" **");  
15.     }  
16.     public void doFilter(ServletRequest req,ServletResponse resp,FilterChain chain)throws IOException,ServletException{  
17.         System.out.println("** 执行doFilter()方法之前. **");  
18.         System.out.println("** 过滤器开始工作 **");  
19.         chain.doFilter(req, resp);  
20.         System.out.println("** 执行doFilter()方法之后. **");  
21.     }  
22.     public void destroy(){  
23.         System.out.println("** 过滤器销毁 **");          
24.     }  
25. }  

[java] view plaincopyprint?

1. package org.lxh.filterdemo;  
2.   
3. import java.io.IOException;  
4. import javax.servlet.Filter;  
5. import javax.servlet.FilterChain;  
6. import javax.servlet.FilterConfig;  
7. import javax.servlet.ServletException;  
8. import javax.servlet.ServletRequest;  
9. import javax.servlet.ServletResponse;  
10.   
11. public class SimpleFilter2 implements Filter{  
12.     public void init(FilterConfig config) throws ServletException{  
13.         String initParam = config.getInitParameter("ref");  
14.         System.out.println("** SimpleFilter2.过滤器初始化，初始化参数="+initParam+" **");  
15.     }  
16.     public void doFilter(ServletRequest req,ServletResponse resp,FilterChain chain)throws IOException,ServletException{  
17.         System.out.println("** 执行SimpleFilter2.doFilter()方法之前. **");  
18.         System.out.println("** SimpleFilter2.过滤器开始工作 **");  
19.         chain.doFilter(req, resp);  
20.         System.out.println("** 执行SimpleFilter2.doFilter()方法之后. **");  
21.     }  
22.     public void destroy(){  
23.         System.out.println("** SimpleFilter2.过滤器销毁 **");          
24.     }  
25. }  

web.xml

[html] view plaincopyprint?

1. <filter>  
2.     <filter-name>simple</filter-name>  
3.     <filter-class>org.lxh.filterdemo.SimpleFilter</filter-class>  
4.     <init-param>  
5.         <param-name>ref</param-name>  
6.         <param-value>HELLO WORLD</param-value>  
7.     </init-param>  
8. </filter>  
9. <filter-mapping>  
10.     <filter-name>simple</filter-name>  
11.     <url-pattern>/*</url-pattern>  
12. </filter-mapping>  
13. <filter>  
14.     <filter-name>simple2</filter-name>  
15.     <filter-class>org.lxh.filterdemo.SimpleFilter2</filter-class>  
16.     <init-param>  
17.         <param-name>ref</param-name>  
18.         <param-value>HELLO WORLD</param-value>  
19.     </init-param>  
20. </filter>  
21. <filter-mapping>  
22.     <filter-name>simple2</filter-name>  
23.     <url-pattern>/*</url-pattern>  
24. </filter-mapping>  

代码完毕,然后刷新任意Context下的任意页面，输出如下：

** 执行doFilter()方法之前. **
** 过滤器开始工作 **
** 执行SimpleFilter2.doFilter()方法之前. **
** SimpleFilter2.过滤器开始工作 **
** 执行SimpleFilter2.doFilter()方法之后. **
** 执行doFilter()方法之后. **

这时候想想链式处理，每个过滤器都会输出自己的doFilter()方法处理前后。而且最早声明的过滤器会包围最末声明的过滤器。这就是链式的处理特点！


使用ServletFilter的例子有：登录验证，设置Request.setCharacterEncoding编码