編寫Filter的時候,我們需要實現Filter接口,需要去實現init(FilterConfig arg0),doFilter(ServletRequest request, ServletResponse response, FilterChain chain),destroy()等方法,有時候我們並不需要去實現init與destory方法,但又必須在代碼裡面寫上這兩個方法.如果我們不想多寫這個兩個方法,我們可以用一個類去實現Filter接口,在我們開發的時候直接繼承這個類,實現doFilter方法即可.
代碼如下:
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 * 自定義的HttpFilter,實現Filter接口,參考自GenericServlet的實現方式
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 * 該方法由servlet容器進行調用,有且只調用一次
27 * 不建議子類直接重寫該方法
28 */
29 @Override
30 public void init(FilterConfig arg0) throws ServletException {
31 this.filterConfig = arg0;
32 this.init();
33 }
34
35 /**
36 * 供子類重寫的初始化方法,在子類中可以在init()方法中調用getFilterConfig()方法來獲取FilterConfig對象,來獲取初始化參數
37 * @throws ServletException
38 */
39 protected void init() throws ServletException {
40 //TODO Auto-generated method stub
41 }
42
43 /**
44 * 供子類調用,來獲取FilterConfig對象
45 * @return
46 */
47 public FilterConfig getFilterConfig() {
48 return filterConfig;
49 }
50
51 /**
52 * 該方法由servlet容器調用,不建議之類直接進行重寫
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 * 該方法由子類必須重寫的過濾方法
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容器進行調用
83 */
84 @Override
85 public void destroy() {
86 // TODO Auto-generated method stub
87
88 }
89
90 }
開發的時候我們只需新建一個類,然後去繼承HttpFilter即可.如果有初始化的需要,建議重寫無參的init()方法,如果想在該方法內使用FilterConfig對象,通過調用this.getFilterConfig()方法即可獲得.編寫過濾方法時建議重寫doFilter(HttpServletRequest request, HttpServletResponse response,FilterChain filterChain).該方法的好處是可以直接使用HttpServletRequest,HttpServletResponse,不用自己再去將ServletRequest,ServletResponse對象強制轉換為HttpServletRequest,HttpServletResponse對象.如果有釋放資源等操作的時候,直接重寫destory()方法即可,沒有的話就不用重寫.可以讓代碼看上去更美觀.
