JavaWeb學習 (二十四)————Filter(過濾器)常見應用
阿新 • • 發佈：2019-01-05
一、統一全站字元編碼
通過配置引數charset指明使用何種字元編碼,以處理Html Form請求引數的中文問題
1 package me.gacl.web.filter;
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 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletRequestWrapper;
12 import javax.servlet.http.HttpServletResponse;
13
14 /**
15 * @ClassName: CharacterEncodingFilter
16 * @Description: 此過濾器用來解決全站中文亂碼問題
17 * @author: 孤傲蒼狼
18 * @date: 2014-8-31 下午11:09:37
19 *
20 */
21 public class CharacterEncodingFilter implements Filter {
22
23 private FilterConfig filterConfig = null;
24 //設定預設的字元編碼
25 private String defaultCharset = "UTF-8";
26
27 public void doFilter(ServletRequest req, ServletResponse resp,
28 FilterChain chain) throws IOException, ServletException {
29
30 HttpServletRequest request = (HttpServletRequest) req;
31 HttpServletResponse response = (HttpServletResponse) resp;
32 String charset = filterConfig.getInitParameter("charset");
33 if(charset==null){
34 charset = defaultCharset;
35 }
36 request.setCharacterEncoding(charset);
37 response.setCharacterEncoding(charset);
38 response.setContentType("text/html;charset="+charset);
39
40 MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request);
41 chain.doFilter(requestWrapper, response);
42 }
43
44 public void init(FilterConfig filterConfig) throws ServletException {
45 //得到過濾器的初始化配置資訊
46 this.filterConfig = filterConfig;
47 }
48
49 public void destroy() {
50
51 }
52 }
53
54 /*
55 1.實現與被增強物件相同的介面
56 2、定義一個變數記住被增強物件
57 3、定義一個構造器，接收被增強物件
58 4、覆蓋需要增強的方法
59 5、對於不想增強的方法，直接呼叫被增強物件（目標物件）的方法
60 */
61
62 class MyCharacterEncodingRequest extends HttpServletRequestWrapper{
63
64 private HttpServletRequest request;
65 public MyCharacterEncodingRequest(HttpServletRequest request) {
66 super(request);
67 this.request = request;
68 }
69 /* 重寫getParameter方法
70 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
71 */
72 @Override
73 public String getParameter(String name) {
74
75 try{
76 //獲取引數的值
77 String value= this.request.getParameter(name);
78 if(value==null){
79 return null;
80 }
81 //如果不是以get方式提交資料的，就直接返回獲取到的值
82 if(!this.request.getMethod().equalsIgnoreCase("get")) {
83 return value;
84 }else{
85 //如果是以get方式提交資料的，就對獲取到的值進行轉碼處理
86 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());
87 return value;
88 }
89 }catch (Exception e) {
90 throw new RuntimeException(e);
91 }
92 }
93 }
web.xml檔案中的配置如下：
1 <filter> 2 <filter-name>CharacterEncodingFilter</filter-name> 3 <filter-class>me.gacl.web.filter.CharacterEncodingFilter</filter-class> 4 <init-param> 5 <param-name>charset</param-name> 6 <param-value>UTF-8</param-value> 7 </init-param> 8 </filter> 9 10 <filter-mapping> 11 <filter-name>CharacterEncodingFilter</filter-name> 12 <url-pattern>/*</url-pattern> 13 </filter-mapping>
二、禁止瀏覽器快取所有動態頁面
有3 個HTTP 響應頭欄位都可以禁止瀏覽器快取當前頁面，它們在 Servlet 中的示例程式碼如下：
1 response.setDateHeader("Expires",-1);
2 response.setHeader("Cache-Control","no-cache");
3 response.setHeader("Pragma","no-cache");
並不是所有的瀏覽器都能完全支援上面的三個響應頭，因此最好是同時使用上面的三個響應頭。
- Expires資料頭：值為GMT時間值，為-1指瀏覽器不要快取頁面
- Cache-Control響應頭有兩個常用值：
- no-cache指瀏覽器不要快取當前頁面。
- max-age:xxx指瀏覽器快取頁面xxx秒。
1 package me.gacl.web.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 * @ClassName: NoCacheFilter
16 * @Description: 禁止瀏覽器快取所有動態頁面
17 * @author: 孤傲蒼狼
18 * @date: 2014-8-31 下午11:25:40
19 *
20 */
21 public class NoCacheFilter implements Filter {
22
23
24 public void doFilter(ServletRequest req, ServletResponse resp,
25 FilterChain chain) throws IOException, ServletException {
26 //把ServletRequest強轉成HttpServletRequest
27 HttpServletRequest request = (HttpServletRequest) req;
28 //把ServletResponse強轉成HttpServletResponse
29 HttpServletResponse response = (HttpServletResponse) resp;
30 //禁止瀏覽器快取所有動態頁面
31 response.setDateHeader("Expires", -1);
32 response.setHeader("Cache-Control", "no-cache");
33 response.setHeader("Pragma", "no-cache");
34
35 chain.doFilter(request, response);
36 }
37
38 public void init(FilterConfig filterConfig) throws ServletException {
39
40 }
41
42 public void destroy() {
43
44 }
45 }
web.xml檔案中的配置如下：
1 <filter> 2 <filter-name>NoCacheFilter</filter-name> 3 <filter-class>me.gacl.web.filter.NoCacheFilter</filter-class> 4 </filter> 5 6 <filter-mapping> 7 <filter-name>NoCacheFilter</filter-name> 8 <!--只攔截Jsp請求--> 9 <servlet-name>*.jsp</servlet-name> 10 </filter-mapping>
三、控制瀏覽器快取頁面中的靜態資源
有些動態頁面中引用了一些圖片或css檔案以修飾頁面效果，這些圖片和css檔案經常是不變化的，所以為減輕伺服器的壓力，可以使用filter控制瀏覽器快取這些檔案，以提升伺服器的效能。
1 package me.gacl.web.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 * @ClassName: CacheFilter
16 * @Description: 控制快取的filter
17 * @author: 孤傲蒼狼
18 * @date: 2014-9-1 下午9:39:38
19 *
20 */
21 public class CacheFilter implements Filter {
22
23 private FilterConfig filterConfig;
24
25 public void doFilter(ServletRequest req, ServletResponse resp,
26 FilterChain chain) throws IOException, ServletException {
27
28 HttpServletRequest request = (HttpServletRequest) req;
29 HttpServletResponse response = (HttpServletResponse) resp;
30
31 //1.獲取使用者想訪問的資源
32 String uri = request.getRequestURI();
33
34 //2.得到使用者想訪問的資源的字尾名
35 String ext = uri.substring(uri.lastIndexOf(".")+1);
36
37 //得到資源需要快取的時間
38 String time = filterConfig.getInitParameter(ext);
39 if(time!=null){
40 long t = Long.parseLong(time)*3600*1000;
41 //設定快取
42 response.setDateHeader("expires", System.currentTimeMillis() + t);
43 }
44
45 chain.doFilter(request, response);
46
47 }
48
49 public void init(FilterConfig filterConfig) throws ServletException {
50 this.filterConfig = filterConfig;
51 }
52
53 public void destroy() {
54
55 }
56 }
web.xml檔案中的配置如下：
1 <!-- 配置快取過濾器 --> 2 <filter> 3 <filter-name>CacheFilter</filter-name> 4 <filter-class>me.gacl.web.filter.CacheFilter</filter-class> 5 <!-- 配置要快取的web資源以及快取時間，以小時為單位 --> 6 <init-param> 7 <param-name>css</param-name> 8 <param-value>4</param-value> 9 </init-param> 10 <init-param> 11 <param-name>jpg</param-name> 12 <param-value>1</param-value> 13 </init-param> 14 <init-param> 15 <param-name>js</param-name> 16 <param-value>4</param-value> 17 </init-param> 18 <init-param> 19 <param-name>png</param-name> 20 <param-value>4</param-value> 21 </init-param> 22 </filter> 23 <!-- 配置要快取的web資源的字尾--> 24 <filter-mapping> 25 <filter-name>CacheFilter</filter-name> 26 <url-pattern>*.jpg</url-pattern> 27 </filter-mapping> 28 29 <filter-mapping> 30 <filter-name>CacheFilter</filter-name> 31 <url-pattern>*.css</url-pattern> 32 </filter-mapping> 33 34 <filter-mapping> 35 <filter-name>CacheFilter</filter-name> 36 <url-pattern>*.js</url-pattern> 37 </filter-mapping> 38 <filter-mapping> 39 <filter-name>CacheFilter</filter-name> 40 <url-pattern>*.png</url-pattern> 41 </filter-mapping>
四、實現使用者自動登陸
思路是這樣的：
1、在使用者登陸成功後，傳送一個名稱為user的cookie給客戶端，cookie的值為使用者名稱和md5加密後的密碼。
2、編寫一個AutoLoginFilter，這個filter檢查使用者是否帶有名稱為user的cookie來，如果有，則呼叫dao查詢cookie的使用者名稱和密碼是否和資料庫匹配，匹配則向session中存入user物件（即使用者登陸標記），以實現程式完成自動登陸。
核心程式碼如下：
處理使用者登入的控制器：LoginServlet
1 package me.gacl.web.controller;
2
3 import java.io.IOException;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.http.Cookie;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10
11 import me.gacl.dao.UserDao;
12 import me.gacl.domain.User;
13 import me.gacl.util.WebUtils;
14
15 public class LoginServlet extends HttpServlet {
16
17 public void doGet(HttpServletRequest request, HttpServletResponse response)
18 throws ServletException, IOException {
19
20 String username = request.getParameter("username");
21 String password = request.getParameter("password");
22
23 UserDao dao = new UserDao();
24 User user = dao.find(username, password);
25 if(user==null){
26 request.setAttribute("message", "使用者名稱或密碼不對！！");
27 request.getRequestDispatcher("/message.jsp").forward(request, response);
28 return;
29 }
30 request.getSession().setAttribute("user", user);
31 //傳送自動登陸cookie給客戶端瀏覽器進行儲存
32 sendAutoLoginCookie(request,response,user);
33 request.getRequestDispatcher("/index.jsp").forward(request, response);
34 }
35
36 /**
37 * @Method: sendAutoLoginCookie
38 * @Description: 傳送自動登入cookie給客戶端瀏覽器
39 * @Anthor:孤傲蒼狼
40 *
41 * @param request
42 * @param response
43 * @param user
44 */
45 private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) {
46 if (request.getParameter("logintime")!=null) {
47 int logintime = Integer.parseInt(request.getParameter("logintime"));
48 //建立cookie,cookie的名字是autologin，值是使用者登入的使用者名稱和密碼，使用者名稱和密碼之間使用.進行分割，密碼經過md5加密處理
49 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword()));
50 //設定cookie的有效期
51 cookie.setMaxAge(logintime);
52 //設定cookie的有效路徑
53 cookie.setPath(request.getContextPath());
54 //將cookie寫入到客戶端瀏覽器
55 response.addCookie(cookie);
56 }
57 }
58
59 public void doPost(HttpServletRequest request, HttpServletResponse response)
60 throws ServletException, IOException {
61
62 doGet(request, response);
63 }
64
65 }
處理使用者自動登入的過濾器：AutoLoginFilter
1 package me.gacl.web.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.Cookie;
12 import javax.servlet.http.HttpServletRequest;
13 import javax.servlet.http.HttpServletResponse;
14
15 import me.gacl.dao.UserDao;
16 import me.gacl.domain.User;
17 import me.gacl.util.WebUtils;
18
19 public class AutoLoginFilter implements Filter {
20
21 public void doFilter(ServletRequest req, ServletResponse resp,
22 FilterChain chain) throws IOException, ServletException {
23
24 HttpServletRequest request = (HttpServletRequest) req;
25 HttpServletResponse response = (HttpServletResponse) resp;
26 //如果已經登入了，就直接chain.doFilter(request, response)放行
27 if(request.getSession().getAttribute("user")!=null){
28 chain.doFilter(request, response);
29 return;
30 }
31
32 //1.得到使用者帶過來的authlogin的cookie
33 String value = null;
34 Cookie cookies[] = request.getCookies();
35 for(int i=0;cookies!=null && i<cookies.length;i++){
36 if(cookies[i].getName().equals("autologin")){
37 value = cookies[i].getValue();
38 }
39 }
40
41 //2.得到 cookie中的使用者名稱和密碼
42 if(value!=null){
43 String username = value.split("\\.")[0];
44 String password = value.split("\\.")[1];
45
46 //3.呼叫dao獲取使用者對應的密碼
47 UserDao dao = new UserDao();
48 User user = dao.find(username);
49 String dbpassword = user.getPassword();
50
51 //4.檢查使用者帶過來的md5的密碼和資料庫中的密碼是否匹配,如匹配則自動登陸
52 if(password.equals(WebUtils.md5(dbpassword))){
53 request.getSession().setAttribute("user", user);
54 }
55 }
56
57 chain.doFilter(request, response);
58 }
59
60 public void destroy() {
61
62 }
63
64 public void init(FilterConfig filterConfig) throws ServletException {
65
66 }
67 }
如果想取消自動登入，那麼可以在使用者登出時刪除自動登入cookie，核心程式碼如下：
1 package me.gacl.web.controller;
2
3 import java.io.IOException;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.http.Cookie;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10
11 public class CancelAutoLoginServlet extends HttpServlet {
12
13 public void doGet(HttpServletRequest request, HttpServletResponse response)
14 throws ServletException, IOException {
15 //移除儲存在session中的user
16 request.getSession().removeAttribute("user");
17 //移除自動登入的cookie
18 removeAutoLoginCookie(request,response);
19 //登出使用者後跳轉到登入頁面
20 request.getRequestDispatcher("/login.jsp").forward(request, response);
21 }
22
23 /**
24 * @Method: removeAutoLoginCookie
25 * @Description: 刪除自動登入cookie，
26 * JavaWeb中刪除cookie的方式就是新建立一個cookie，新建立的cookie與要刪除的cookie同名，
27 * 設定新建立的cookie的cookie的有效期設定為0，有效路徑與要刪除的cookie的有效路徑相同
28 * @Anthor:孤傲蒼狼
29 *
30 * @param request
31 * @param response
32 */
33 private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) {
34 //建立一個名字為autologin的cookie
35 Cookie cookie = new Cookie("autologin","");
36 //將cookie的有效期設定為0，命令瀏覽器刪除該cookie
37 cookie.setMaxAge(0);
38 //設定要刪除的cookie的path
39 cookie.setPath(request.getContextPath());
40 response.addCookie(cookie);
41 }
42
43 public void doPost(HttpServletRequest request, HttpServletResponse response)
44 throws ServletException, IOException {
45 doGet(request, response);
46 }
47 }
以上就是過濾器的幾個常見應用場景。
通過配置引數charset指明使用何種字元編碼,以處理Html Form請求引數的中文問題
1 package me.gacl.web.filter;
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 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletRequestWrapper;
12 import javax.servlet.http.HttpServletResponse;
13
14 /**
15 * @ClassName: CharacterEncodingFilter
16 * @Description: 此過濾器用來解決全站中文亂碼問題
17 * @author: 孤傲蒼狼
18 * @date: 2014-8-31 下午11:09:37
19 *
20 */
21 public class CharacterEncodingFilter implements Filter {
22
23 private FilterConfig filterConfig = null;
24 //設定預設的字元編碼
25 private String defaultCharset = "UTF-8";
26
27 public void doFilter(ServletRequest req, ServletResponse resp,
28 FilterChain chain) throws IOException, ServletException {
29
30 HttpServletRequest request = (HttpServletRequest) req;
31 HttpServletResponse response = (HttpServletResponse) resp;
32 String charset = filterConfig.getInitParameter("charset");
33 if(charset==null){
34 charset = defaultCharset;
35 }
36 request.setCharacterEncoding(charset);
37 response.setCharacterEncoding(charset);
38 response.setContentType("text/html;charset="+charset);
39
40 MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request);
41 chain.doFilter(requestWrapper, response);
42 }
43
44 public void init(FilterConfig filterConfig) throws ServletException {
45 //得到過濾器的初始化配置資訊
46 this.filterConfig = filterConfig;
47 }
48
49 public void destroy() {
50
51 }
52 }
53
54 /*
55 1.實現與被增強物件相同的介面
56 2、定義一個變數記住被增強物件
57 3、定義一個構造器，接收被增強物件
58 4、覆蓋需要增強的方法
59 5、對於不想增強的方法，直接呼叫被增強物件（目標物件）的方法
60 */
61
62 class MyCharacterEncodingRequest extends HttpServletRequestWrapper{
63
64 private HttpServletRequest request;
65 public MyCharacterEncodingRequest(HttpServletRequest request) {
66 super(request);
67 this.request = request;
68 }
69 /* 重寫getParameter方法
70 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
71 */
72 @Override
73 public String getParameter(String name) {
74
75 try{
76 //獲取引數的值
77 String value= this.request.getParameter(name);
78 if(value==null){
79 return null;
80 }
81 //如果不是以get方式提交資料的，就直接返回獲取到的值
82 if(!this.request.getMethod().equalsIgnoreCase("get")) {
83 return value;
84 }else{
85 //如果是以get方式提交資料的，就對獲取到的值進行轉碼處理
86 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());
87 return value;
88 }
89 }catch (Exception e) {
90 throw new RuntimeException(e);
91 }
92 }
93 }
web.xml檔案中的配置如下：
1 <filter> 2 <filter-name>CharacterEncodingFilter</filter-name> 3 <filter-class>me.gacl.web.filter.CharacterEncodingFilter</filter-class> 4 <init-param> 5 <param-name>charset</param-name> 6 <param-value>UTF-8</param-value> 7 </init-param> 8 </filter> 9 10 <filter-mapping> 11 <filter-name>CharacterEncodingFilter</filter-name> 12 <url-pattern>/*</url-pattern> 13 </filter-mapping>
二、禁止瀏覽器快取所有動態頁面
有3 個HTTP 響應頭欄位都可以禁止瀏覽器快取當前頁面，它們在 Servlet 中的示例程式碼如下：
1 response.setDateHeader("Expires",-1);
2 response.setHeader("Cache-Control","no-cache");
3 response.setHeader("Pragma","no-cache");
並不是所有的瀏覽器都能完全支援上面的三個響應頭，因此最好是同時使用上面的三個響應頭。
- Expires資料頭：值為GMT時間值，為-1指瀏覽器不要快取頁面
- Cache-Control響應頭有兩個常用值：
- no-cache指瀏覽器不要快取當前頁面。
- max-age:xxx指瀏覽器快取頁面xxx秒。
1 package me.gacl.web.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 * @ClassName: NoCacheFilter
16 * @Description: 禁止瀏覽器快取所有動態頁面
17 * @author: 孤傲蒼狼
18 * @date: 2014-8-31 下午11:25:40
19 *
20 */
21 public class NoCacheFilter implements Filter {
22
23
24 public void doFilter(ServletRequest req, ServletResponse resp,
25 FilterChain chain) throws IOException, ServletException {
26 //把ServletRequest強轉成HttpServletRequest
27 HttpServletRequest request = (HttpServletRequest) req;
28 //把ServletResponse強轉成HttpServletResponse
29 HttpServletResponse response = (HttpServletResponse) resp;
30 //禁止瀏覽器快取所有動態頁面
31 response.setDateHeader("Expires", -1);
32 response.setHeader("Cache-Control", "no-cache");
33 response.setHeader("Pragma", "no-cache");
34
35 chain.doFilter(request, response);
36 }
37
38 public void init(FilterConfig filterConfig) throws ServletException {
39
40 }
41
42 public void destroy() {
43
44 }
45 }
web.xml檔案中的配置如下：
1 <filter> 2 <filter-name>NoCacheFilter</filter-name> 3 <filter-class>me.gacl.web.filter.NoCacheFilter</filter-class> 4 </filter> 5 6 <filter-mapping> 7 <filter-name>NoCacheFilter</filter-name> 8 <!--只攔截Jsp請求--> 9 <servlet-name>*.jsp</servlet-name> 10 </filter-mapping>
三、控制瀏覽器快取頁面中的靜態資源
有些動態頁面中引用了一些圖片或css檔案以修飾頁面效果，這些圖片和css檔案經常是不變化的，所以為減輕伺服器的壓力，可以使用filter控制瀏覽器快取這些檔案，以提升伺服器的效能。
1 package me.gacl.web.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 * @ClassName: CacheFilter
16 * @Description: 控制快取的filter
17 * @author: 孤傲蒼狼
18 * @date: 2014-9-1 下午9:39:38
19 *
20 */
21 public class CacheFilter implements Filter {
22
23 private FilterConfig filterConfig;
24
25 public void doFilter(ServletRequest req, ServletResponse resp,
26 FilterChain chain) throws IOException, ServletException {
27
28 HttpServletRequest request = (HttpServletRequest) req;
29 HttpServletResponse response = (HttpServletResponse) resp;
30
31 //1.獲取使用者想訪問的資源
32 String uri = request.getRequestURI();
33
34 //2.得到使用者想訪問的資源的字尾名
35 String ext = uri.substring(uri.lastIndexOf(".")+1);
36
37 //得到資源需要快取的時間
38 String time = filterConfig.getInitParameter(ext);
39 if(time!=null){
40 long t = Long.parseLong(time)*3600*1000;
41 //設定快取
42 response.setDateHeader("expires", System.currentTimeMillis() + t);
43 }
44
45 chain.doFilter(request, response);
46
47 }
48
49 public void init(FilterConfig filterConfig) throws ServletException {
50 this.filterConfig = filterConfig;
51 }
52
53 public void destroy() {
54
55 }
56 }
web.xml檔案中的配置如下：
1 <!-- 配置快取過濾器 --> 2 <filter> 3 <filter-name>CacheFilter</filter-name> 4 <filter-class>me.gacl.web.filter.CacheFilter</filter-class> 5 <!-- 配置要快取的web資源以及快取時間，以小時為單位 --> 6 <init-param> 7 <param-name>css</param-name> 8 <param-value>4</param-value> 9 </init-param> 10 <init-param> 11 <param-name>jpg</param-name> 12 <param-value>1</param-value> 13 </init-param> 14 <init-param> 15 <param-name>js</param-name> 16 <param-value>4</param-value> 17 </init-param> 18 <init-param> 19 <param-name>png</param-name> 20 <param-value>4</param-value> 21 </init-param> 22 </filter> 23 <!-- 配置要快取的web資源的字尾--> 24 <filter-mapping> 25 <filter-name>CacheFilter</filter-name> 26 <url-pattern>*.jpg</url-pattern> 27 </filter-mapping> 28 29 <filter-mapping> 30 <filter-name>CacheFilter</filter-name> 31 <url-pattern>*.css</url-pattern> 32 </filter-mapping> 33 34 <filter-mapping> 35 <filter-name>CacheFilter</filter-name> 36 <url-pattern>*.js</url-pattern> 37 </filter-mapping> 38 <filter-mapping> 39 <filter-name>CacheFilter</filter-name> 40 <url-pattern>*.png</url-pattern> 41 </filter-mapping>
四、實現使用者自動登陸
思路是這樣的：
1、在使用者登陸成功後，傳送一個名稱為user的cookie給客戶端，cookie的值為使用者名稱和md5加密後的密碼。
2、編寫一個AutoLoginFilter，這個filter檢查使用者是否帶有名稱為user的cookie來，如果有，則呼叫dao查詢cookie的使用者名稱和密碼是否和資料庫匹配，匹配則向session中存入user物件（即使用者登陸標記），以實現程式完成自動登陸。
核心程式碼如下：
處理使用者登入的控制器：LoginServlet
1 package me.gacl.web.controller;
2
3 import java.io.IOException;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.http.Cookie;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10
11 import me.gacl.dao.UserDao;
12 import me.gacl.domain.User;
13 import me.gacl.util.WebUtils;
14
15 public class LoginServlet extends HttpServlet {
16
17 public void doGet(HttpServletRequest request, HttpServletResponse response)
18 throws ServletException, IOException {
19
20 String username = request.getParameter("username");
21 String password = request.getParameter("password");
22
23 UserDao dao = new UserDao();
24 User user = dao.find(username, password);
25 if(user==null){
26 request.setAttribute("message", "使用者名稱或密碼不對！！");
27 request.getRequestDispatcher("/message.jsp").forward(request, response);
28 return;
29 }
30 request.getSession().setAttribute("user", user);
31 //傳送自動登陸cookie給客戶端瀏覽器進行儲存
32 sendAutoLoginCookie(request,response,user);
33 request.getRequestDispatcher("/index.jsp").forward(request, response);
34 }
35
36 /**
37 * @Method: sendAutoLoginCookie
38 * @Description: 傳送自動登入cookie給客戶端瀏覽器
39 * @Anthor:孤傲蒼狼
40 *
41 * @param request
42 * @param response
43 * @param user
44 */
45 private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) {
46 if (request.getParameter("logintime")!=null) {
47 int logintime = Integer.parseInt(request.getParameter("logintime"));
48 //建立cookie,cookie的名字是autologin，值是使用者登入的使用者名稱和密碼，使用者名稱和密碼之間使用.進行分割，密碼經過md5加密處理
49 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword()));
50 //設定cookie的有效期
51 cookie.setMaxAge(logintime);
52 //設定cookie的有效路徑
53 cookie.setPath(request.getContextPath());
54 //將cookie寫入到客戶端瀏覽器
55 response.addCookie(cookie);
56 }
57 }
58
59 public void doPost(HttpServletRequest request, HttpServletResponse response)
60 throws ServletException, IOException {
61
62 doGet(request, response);
63 }
64
65 }
處理使用者自動登入的過濾器：AutoLoginFilter
1 package me.gacl.web.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.Cookie;
12 import javax.servlet.http.HttpServletRequest;
13 import javax.servlet.http.HttpServletResponse;
14
15 import me.gacl.dao.UserDao;
16 import me.gacl.domain.User;
17 import me.gacl.util.WebUtils;
18
19 public class AutoLoginFilter implements Filter {
20
21 public void doFilter(ServletRequest req, ServletResponse resp,
22 FilterChain chain) throws IOException, ServletException {
23
24 HttpServletRequest request = (HttpServletRequest) req;
25 HttpServletResponse response = (HttpServletResponse) resp;
26 //如果已經登入了，就直接chain.doFilter(request, response)放行
27 if(request.getSession().getAttribute("user")!=null){
28 chain.doFilter(request, response);
29 return;
30 }
31
32 //1.得到使用者帶過來的authlogin的cookie
33 String value = null;
34 Cookie cookies[] = request.getCookies();
35 for(int i=0;cookies!=null && i<cookies.length;i++){
36 if(cookies[i].getName().equals("autologin")){
37 value = cookies[i].getValue();
38 }
39 }
40
41 //2.得到 cookie中的使用者名稱和密碼
42 if(value!=null){
43 String username = value.split("\\.")[0];
44 String password = value.split("\\.")[1];
45
46 //3.呼叫dao獲取使用者對應的密碼
47 UserDao dao = new UserDao();
48 User user = dao.find(username);
49 String dbpassword = user.getPassword();
50
51 //4.檢查使用者帶過來的md5的密碼和資料庫中的密碼是否匹配,如匹配則自動登陸
52 if(password.equals(WebUtils.md5(dbpassword))){
53 request.getSession().setAttribute("user", user);
54 }
55 }
56
57 chain.doFilter(request, response);
58 }
59
60 public void destroy() {
61
62 }
63
64 public void init(FilterConfig filterConfig) throws ServletException {
65
66 }
67 }
如果想取消自動登入，那麼可以在使用者登出時刪除自動登入cookie，核心程式碼如下：
1 package me.gacl.web.controller;
2
3 import java.io.IOException;
4
5 import javax.servlet.ServletException;
6 import javax.servlet.http.Cookie;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10
11 public class CancelAutoLoginServlet extends HttpServlet {
12
13 public void doGet(HttpServletRequest request, HttpServletResponse response)
14 throws ServletException, IOException {
15 //移除儲存在session中的user
16 request.getSession().removeAttribute("user");
17 //移除自動登入的cookie
18 removeAutoLoginCookie(request,response);
19 //登出使用者後跳轉到登入頁面
20 request.getRequestDispatcher("/login.jsp").forward(request, response);
21 }
22
23 /**
24 * @Method: removeAutoLoginCookie
25 * @Description: 刪除自動登入cookie，
26 * JavaWeb中刪除cookie的方式就是新建立一個cookie，新建立的cookie與要刪除的cookie同名，
27 * 設定新建立的cookie的cookie的有效期設定為0，有效路徑與要刪除的cookie的有效路徑相同
28 * @Anthor:孤傲蒼狼
29 *
30 * @param request
31 * @param response
32 */
33 private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) {
34 //建立一個名字為autologin的cookie
35 Cookie cookie = new Cookie("autologin","");
36 //將cookie的有效期設定為0，命令瀏覽器刪除該cookie
37 cookie.setMaxAge(0);
38 //設定要刪除的cookie的path
39 cookie.setPath(request.getContextPath());
40 response.addCookie(cookie);
41 }
42
43 public void doPost(HttpServletRequest request, HttpServletResponse response)
44 throws ServletException, IOException {
45 doGet(request, response);
46 }
47 }
以上就是過濾器的幾個常見應用場景。