像GenericServlet实现Servlet接口的方式去实现Filter接口

编写Filter的时候,我们需要实现Filter接口,需要去实现init(FilterConfig arg0),doFilter(ServletRequest request, ServletResponse response, FilterChain chain),destroy()等方法,有时候我们并不需要去实现init与destory方法,但又必须在代码里面写上这两个方法.如果我们不想多写这个两个方法,我们可以用一个类去实现Filter接口,在我们开发的时候直接继承这个类,实现doFilter方法即可.

代码如下:

 1 package com.zhx.http.filter;
 2
 3 import java.io.IOException;
 4
 5 import javax.servlet.Filter;
 6 import javax.servlet.FilterChain;
 7 import javax.servlet.FilterConfig;
 8 import javax.servlet.ServletException;
 9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13
14 /**
15  *
16  * @author zhaoxin
17  * 自定义的HttpFilter,实现Filter接口,参考自GenericServlet的实现方式
18  */
19 public abstract class HttpFilter implements Filter,java.io.Serializable {
20
21     private static final long serialVersionUID = 1L;
22
23     private FilterConfig filterConfig;
24
25     /**
26      * 该方法由servlet容器进行调用,有且只调用一次
27      * 不建议子类直接重写该方法
28      */
29     @Override
30     public void init(FilterConfig arg0) throws ServletException {
31         this.filterConfig = arg0;
32         this.init();
33     }
34
35     /**
36      * 供子类重写的初始化方法,在子类中可以在init()方法中调用getFilterConfig()方法来获取FilterConfig对象,来获取初始化参数
37      * @throws ServletException
38      */
39     protected void init() throws ServletException {
40         //TODO Auto-generated method stub
41     }
42
43     /**
44      * 供子类调用,来获取FilterConfig对象
45      * @return
46      */
47     public FilterConfig getFilterConfig() {
48         return filterConfig;
49     }
50
51     /**
52      * 该方法由servlet容器调用,不建议之类直接进行重写
53      */
54     @Override
55     public void doFilter(ServletRequest req, ServletResponse res,
56             FilterChain fc) throws IOException, ServletException {
57
58         HttpServletRequest request;
59         HttpServletResponse response;
60
61         try {
62             request = (HttpServletRequest)req;
63             response = (HttpServletResponse)res;
64         } catch (Exception e) {
65              throw new ServletException("non-HTTP request or response");
66         }
67         doFilter(request, response, fc);
68     }
69
70     /**
71      * 该方法由子类必须重写的过滤方法
72      * @param request
73      * @param response
74      * @param filterChain
75      * @throws IOException
76      * @throws ServletException
77      */
78     public abstract void doFilter(HttpServletRequest request, HttpServletResponse response,
79             FilterChain filterChain) throws IOException, ServletException;
80
81     /**
82      * 由servlet容器进行调用
83      */
84     @Override
85     public void destroy() {
86         // TODO Auto-generated method stub
87
88     }
89
90 }

开发的时候我们只需新建一个类,然后去继承HttpFilter即可.如果有初始化的需要,建议重写无参的init()方法,如果想在该方法内使用FilterConfig对象,通过调用this.getFilterConfig()方法即可获得.编写过滤方法时建议重写doFilter(HttpServletRequest request, HttpServletResponse response,FilterChain filterChain).该方法的好处是可以直接使用HttpServletRequest,HttpServletResponse,不用自己再去将ServletRequest,ServletResponse对象强制转换为HttpServletRequest,HttpServletResponse对象.如果有释放资源等操作的时候,直接重写destory()方法即可,没有的话就不用重写.可以让代码看上去更美观.