转载：javaweb学习总结(四十六)——Filter(过滤器)常见应用

javaweb学习总结(四十六)——Filter(过滤器)常见应用

转自：http://www.cnblogs.com/xdp-gacl/p/3948422.html

1、统一全站字符编码

　　经过配置参数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 //获得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.实现与被加强对象相同的接口 56 二、定义一个变量记住被加强对象 57 三、定义一个构造器，接收被加强对象 58 四、覆盖须要加强的方法 59 五、对于不想加强的方法，直接调用被加强对象（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 //若是不是以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 //若是是以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文件中的配置以下：

 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>

2、禁止浏览器缓存全部动态页面

　　有3 个HTTP 响应头字段均可以禁止浏览器缓存当前页面，它们在 Servlet 中的示例代码以下：

1 response.setDateHeader("Expires",-1); 2 response.setHeader("Cache-Control","no-cache"); 3 response.setHeader("Pragma","no-cache"); 

　　并非全部的浏览器都能彻底支持上面的三个响应头，所以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响应头有两个经常使用值：
• 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: 禁止浏览器缓存全部动态页面 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 //禁止浏览器缓存全部动态页面 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文件中的配置以下：

 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>

3、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文件常常是不变化的，因此为减轻服务器的压力，能够使用filter控制浏览器缓存这些文件，以提高服务器的性能。

 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.获得用户想访问的资源的后缀名 35 String ext = uri.substring(uri.lastIndexOf(".")+1); 36 37 //获得资源须要缓存的时间 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文件中的配置以下：

 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>

4、实现用户自动登录

　　思路是这样的：

　　一、在用户登录成功后，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。
　　二、编写一个AutoLoginFilter，这个filter检查用户是否带有名称为user的cookie来，若是有，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（即用户登录标记），以实现程序完成自动登录。

　　核心代码以下：

　　处理用户登陆的控制器：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 //发送自动登录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: 发送自动登陆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 //建立cookie,cookie的名字是autologin，值是用户登陆的用户名和密码，用户名和密码之间使用.进行分割，密码通过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 }

　　处理用户自动登陆的过滤器：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 //若是已经登陆了，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.获得用户带过来的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.获得 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,如匹配则自动登录 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 }

　　若是想取消自动登陆，那么能够在用户注销时删除自动登陆cookie，核心代码以下：

 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 //移除自动登陆的cookie 18  removeAutoLoginCookie(request,response); 19 //注销用户后跳转到登陆页面 20 request.getRequestDispatcher("/login.jsp").forward(request, response); 21  } 22 23 /** 24  * @Method: removeAutoLoginCookie 25  * @Description: 删除自动登陆cookie， 26  * JavaWeb中删除cookie的方式就是新建立一个cookie，新建立的cookie与要删除的cookie同名， 27  * 设置新建立的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 //建立一个名字为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。