一、统一全站字符编码
通过配置参数charset指明使用何种字符编码,以处理Html Form请求参数的中文问题
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: 此过滤器用来解决全站中文乱码问题
17 * @author: 孤傲苍狼
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 //设置默认的字符编码
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 //得到过滤器的初始化配置信息
46 this.filterConfig = filterConfig;
47 }
48
49 public void destroy() {
50
51 }
52 }
53
54 /*
55 1.实现与被增强对象相同的接口
56 2、定义一个变量记住被增强对象
57 3、定义一个构造器，接收被增强对象
58 4、覆盖需要增强的方法
59 5、对于不想增强的方法，直接调用被增强对象（目标对象）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 /* 重写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 //获取参数的值
77 String value= this.request.getParameter(name);
78 if(value==null){
79 return null;
80 }
81 //如果不是以get方式提交数据的，就直接返回获取到的值
82 if(!this.request.getMethod().equalsIgnoreCase("get")) {
83 return value;
84 }else{
85 //如果是以get方式提交数据的，就对获取到的值进行转码处理
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文件中的配置如下：
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、禁止浏览器缓存所有动态页面
有3 个HTTP 响应头字段都可以禁止浏览器缓存当前页面，它们在 Servlet 中的示例代码如下：
1 response.setDateHeader("Expires",-1);
2 response.setHeader("Cache-Control","no-cache");
3 response.setHeader("Pragma","no-cache");
并不是所有的浏览器都能完全支持上面的三个响应头，因此最好是同时使用上面的三个响应头。
- Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面
- Cache-Control响应头有两个常用值：
- no-cache指浏览器不要缓存当前页面。
- max-age:xxx指浏览器缓存页面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: 禁止浏览器缓存所有动态页面
17 * @author: 孤傲苍狼
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强转成HttpServletRequest
27 HttpServletRequest request = (HttpServletRequest) req;
28 //把ServletResponse强转成HttpServletResponse
29 HttpServletResponse response = (HttpServletResponse) resp;
30 //禁止浏览器缓存所有动态页面
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文件中的配置如下：
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 <!--只拦截Jsp请求-->
9 <servlet-name>*.jsp</servlet-name>
10 </filter-mapping>
三、控制浏览器缓存页面中的静态资源
有些动态页面中引用了一些图片或css文件以修饰页面效果，这些图片和css文件经常是不变化的，所以为减轻服务器的压力，可以使用filter控制浏览器缓存这些文件，以提升服务器的性能。
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: 控制缓存的filter
17 * @author: 孤傲苍狼
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.获取用户想访问的资源
32 String uri = request.getRequestURI();
33
34 //2.得到用户想访问的资源的后缀名
35 String ext = uri.substring(uri.lastIndexOf(".")+1);
36
37 //得到资源需要缓存的时间
38 String time = filterConfig.getInitParameter(ext);
39 if(time!=null){
40 long t = Long.parseLong(time)*3600*1000;
41 //设置缓存
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文件中的配置如下：
1 <!-- 配置缓存过滤器 -->
2 <filter>
3 <filter-name>CacheFilter</filter-name>
4 <filter-class>me.gacl.web.filter.CacheFilter</filter-class>
5 <!-- 配置要缓存的web资源以及缓存时间，以小时为单位 -->
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 <!-- 配置要缓存的web资源的后缀-->
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、实现用户自动登陆
思路是这样的：
1、在用户登陆成功后，发送一个名称为user的cookie给客户端，cookie的值为用户名和md5加密后的密码。
2、编写一个AutoLoginFilter，这个filter检查用户是否带有名称为user的cookie来，如果有，则调用dao查询cookie的用户名和密码是否和数据库匹配，匹配则向session中存入user对象（即用户登陆标记），以实现程序完成自动登陆。
核心代码如下：
处理用户登录的控制器：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", "用户名或密码不对！！");
27 request.getRequestDispatcher("/message.jsp").forward(request, response);
28 return;
29 }
30 request.getSession().setAttribute("user", user);
31 //发送自动登陆cookie给客户端浏览器进行存储
32 sendAutoLoginCookie(request,response,user);
33 request.getRequestDispatcher("/index.jsp").forward(request, response);
34 }
35
36 /**
37 * @Method: sendAutoLoginCookie
38 * @Description: 发送自动登录cookie给客户端浏览器
39 * @Anthor:孤傲苍狼
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 //创建cookie,cookie的名字是autologin，值是用户登录的用户名和密码，用户名和密码之间使用.进行分割，密码经过md5加密处理
49 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword()));
50 //设置cookie的有效期
51 cookie.setMaxAge(logintime);
52 //设置cookie的有效路径
53 cookie.setPath(request.getContextPath());
54 //将cookie写入到客户端浏览器
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 }
处理用户自动登录的过滤器：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 //如果已经登录了，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.得到用户带过来的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中的用户名和密码
42 if(value!=null){
43 String username = value.split("\\.")[0];
44 String password = value.split("\\.")[1];
45
46 //3.调用dao获取用户对应的密码
47 UserDao dao = new UserDao();
48 User user = dao.find(username);
49 String dbpassword = user.getPassword();
50
51 //4.检查用户带过来的md5的密码和数据库中的密码是否匹配,如匹配则自动登陆
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 }
如果想取消自动登录，那么可以在用户注销时删除自动登录cookie，核心代码如下：
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 //移除存储在session中的user
16 request.getSession().removeAttribute("user");
17 //移除自动登录的cookie
18 removeAutoLoginCookie(request,response);
19 //注销用户后跳转到登录页面
20 request.getRequestDispatcher("/login.jsp").forward(request, response);
21 }
22
23 /**
24 * @Method: removeAutoLoginCookie
25 * @Description: 删除自动登录cookie，
26 * JavaWeb中删除cookie的方式就是新创建一个cookie，新创建的cookie与要删除的cookie同名，
27 * 设置新创建的cookie的cookie的有效期设置为0，有效路径与要删除的cookie的有效路径相同
28 * @Anthor:孤傲苍狼
29 *
30 * @param request
31 * @param response
32 */
33 private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) {
34 //创建一个名字为autologin的cookie
35 Cookie cookie = new Cookie("autologin","");
36 //将cookie的有效期设置为0，命令浏览器删除该cookie
37 cookie.setMaxAge(0);
38 //设置要删除的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 }
以上就是过滤器的几个常见应用场景。