一、統一全站字符編碼
通過配置參數charset指明使用何種字符編碼,以處理Html Form請求參數的中文問題
package me.gacl.web.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import javax.servlet.http.HttpServletResponse;/*** @ClassName: CharacterEncodingFilter* @Description: 此過濾器用來解決全站中文亂碼問題*/ public class CharacterEncodingFilter implements Filter { private FilterConfig filterConfig = null; //設置默認的字符編碼 private String defaultCharset = "UTF-8"; public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; String charset = filterConfig.getInitParameter("charset"); if(charset==null){ charset = defaultCharset; } request.setCharacterEncoding(charset); response.setCharacterEncoding(charset); response.setContentType("text/html;charset="+charset); MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request); chain.doFilter(requestWrapper, response); } public void init(FilterConfig filterConfig) throws ServletException { //得到過濾器的初始化配置信息 this.filterConfig = filterConfig; } public void destroy() { }}/*1.實現與被增強對象相同的接口 2、定義一個變量記住被增強對象3、定義一個構造器，接收被增強對象4、覆蓋需要增強的方法5、對于不想增強的方法，直接調用被增強對象（目標對象）的方法 */ class MyCharacterEncodingRequest extends HttpServletRequestWrapper{ private HttpServletRequest request; public MyCharacterEncodingRequest(HttpServletRequest request) { super(request); this.request = request; } /* 重寫getParameter方法 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String) */ @Override public String getParameter(String name) { try{ //獲取參數的值 String value= this.request.getParameter(name); if(value==null){ return null; } //如果不是以get方式提交數據的，就直接返回獲取到的值 if(!this.request.getMethod().equalsIgnoreCase("get")) { return value; }else{ //如果是以get方式提交數據的，就對獲取到的值進行轉碼處理 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding()); return value; } }catch (Exception e) { throw new RuntimeException(e); } }}web.xml文件中的配置如下：
<filter> <filter-name>CharacterEncodingFilter</filter-name> <filter-class>me.gacl.web.filter.CharacterEncodingFilter</filter-class> <init-param> <param-name>charset</param-name> <param-value>UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
二、禁止瀏覽器緩存所有動態頁面
有3 個HTTP 響應頭字段都可以禁止瀏覽器緩存當前頁面，它們在 Servlet 中的示例代碼如下：
并不是所有的瀏覽器都能完全支持上面的三個響應頭，因此最好是同時使用上面的三個響應頭。
package me.gacl.web.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/*** @ClassName: NoCacheFilter* @Description: 禁止瀏覽器緩存所有動態頁面* @author: 孤傲蒼狼* @date: 2014-8-31 下午11:25:40**/ public class NoCacheFilter implements Filter { public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { //把ServletRequest強轉成HttpServletRequest HttpServletRequest request = (HttpServletRequest) req; //把ServletResponse強轉成HttpServletResponse HttpServletResponse response = (HttpServletResponse) resp; //禁止瀏覽器緩存所有動態頁面 response.setDateHeader("Expires", -1); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); chain.doFilter(request, response); } public void init(FilterConfig filterConfig) throws ServletException { } public void destroy() { }}web.xml文件中的配置如下：
<filter> <filter-name>NoCacheFilter</filter-name> <filter-class>me.gacl.web.filter.NoCacheFilter</filter-class> </filter> <filter-mapping> <filter-name>NoCacheFilter</filter-name> <!--只攔截Jsp請求--> <servlet-name>*.jsp</servlet-name> </filter-mapping>
三、控制瀏覽器緩存頁面中的靜態資源
有些動態頁面中引用了一些圖片或css文件以修飾頁面效果，這些圖片和css文件經常是不變化的，所以為減輕服務器的壓力，可以使用filter控制瀏覽器緩存這些文件，以提升服務器的性能。
package me.gacl.web.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/*** @ClassName: CacheFilter* @Description: 控制緩存的filter*/ public class CacheFilter implements Filter { private FilterConfig filterConfig; public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; //1.獲取用戶想訪問的資源 String uri = request.getRequestURI(); //2.得到用戶想訪問的資源的后綴名 String ext = uri.substring(uri.lastIndexOf(".")+1); //得到資源需要緩存的時間 String time = filterConfig.getInitParameter(ext); if(time!=null){ long t = Long.parseLong(time)*3600*1000; //設置緩存 response.setDateHeader("expires", System.currentTimeMillis() + t); } chain.doFilter(request, response); } public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig = filterConfig; } public void destroy() { }}web.xml文件中的配置如下：
<!-- 配置緩存過濾器 --> <filter> <filter-name>CacheFilter</filter-name> <filter-class>me.gacl.web.filter.CacheFilter</filter-class> <!-- 配置要緩存的web資源以及緩存時間，以小時為單位 --> <init-param> <param-name>css</param-name> <param-value>4</param-value> </init-param> <init-param> <param-name>jpg</param-name> <param-value>1</param-value> </init-param> <init-param> <param-name>js</param-name> <param-value>4</param-value> </init-param> <init-param> <param-name>png</param-name> <param-value>4</param-value> </init-param> </filter> <!-- 配置要緩存的web資源的后綴--> <filter-mapping> <filter-name>CacheFilter</filter-name> <url-pattern>*.jpg</url-pattern> </filter-mapping> <filter-mapping> <filter-name>CacheFilter</filter-name> <url-pattern>*.css</url-pattern> </filter-mapping> <filter-mapping> <filter-name>CacheFilter</filter-name> <url-pattern>*.js</url-pattern> </filter-mapping> <filter-mapping> <filter-name>CacheFilter</filter-name> <url-pattern>*.png</url-pattern> </filter-mapping>
四、實現用戶自動登陸
思路是這樣的：
1、在用戶登陸成功后，發送一個名稱為user的cookie給客戶端，cookie的值為用戶名和md5加密后的密碼。
2、編寫一個AutoLoginFilter，這個filter檢查用戶是否帶有名稱為user的cookie來，如果有，則調用dao查詢cookie的用戶名和密碼是否和數據庫匹配，匹配則向session中存入user對象（即用戶登陸標記），以實現程序完成自動登陸。
核心代碼如下：
處理用戶登錄的控制器：LoginServlet
package me.gacl.web.controller;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import me.gacl.dao.UserDao;import me.gacl.domain.User;import me.gacl.util.WebUtils;public class LoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); UserDao dao = new UserDao(); User user = dao.find(username, password); if(user==null){ request.setAttribute("message", "用戶名或密碼不對！！"); request.getRequestDispatcher("/message.jsp").forward(request, response); return; } request.getSession().setAttribute("user", user); //發送自動登陸cookie給客戶端瀏覽器進行存儲 sendAutoLoginCookie(request,response,user); request.getRequestDispatcher("/index.jsp").forward(request, response); } /** * @Method: sendAutoLoginCookie * @Description: 發送自動登錄cookie給客戶端瀏覽器 * @param request * @param response * @param user */ private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) { if (request.getParameter("logintime")!=null) { int logintime = Integer.parseInt(request.getParameter("logintime")); //創建cookie,cookie的名字是autologin，值是用戶登錄的用戶名和密碼，用戶名和密碼之間使用.進行分割，密碼經過md5加密處理 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword())); //設置cookie的有效期 cookie.setMaxAge(logintime); //設置cookie的有效路徑 cookie.setPath(request.getContextPath()); //將cookie寫入到客戶端瀏覽器 response.addCookie(cookie); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}處理用戶自動登錄的過濾器：AutoLoginFilter
package me.gacl.web.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import me.gacl.dao.UserDao;import me.gacl.domain.User;import me.gacl.util.WebUtils;public class AutoLoginFilter implements Filter { public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; //如果已經登錄了，就直接chain.doFilter(request, response)放行 if(request.getSession().getAttribute("user")!=null){ chain.doFilter(request, response); return; } //1.得到用戶帶過來的authlogin的cookie String value = null; Cookie cookies[] = request.getCookies(); for(int i=0;cookies!=null && i<cookies.length;i++){ if(cookies[i].getName().equals("autologin")){ value = cookies[i].getValue(); } } //2.得到 cookie中的用戶名和密碼 if(value!=null){ String username = value.split("http://.")[0]; String password = value.split("http://.")[1]; //3.調用dao獲取用戶對應的密碼 UserDao dao = new UserDao(); User user = dao.find(username); String dbpassword = user.getPassword(); //4.檢查用戶帶過來的md5的密碼和數據庫中的密碼是否匹配,如匹配則自動登陸 if(password.equals(WebUtils.md5(dbpassword))){ request.getSession().setAttribute("user", user); } } chain.doFilter(request, response); } public void destroy() { } public void init(FilterConfig filterConfig) throws ServletException { }}如果想取消自動登錄，那么可以在用戶注銷時刪除自動登錄cookie，核心代碼如下：
package me.gacl.web.controller;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class CancelAutoLoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //移除存儲在session中的user request.getSession().removeAttribute("user"); //移除自動登錄的cookie removeAutoLoginCookie(request,response); //注銷用戶后跳轉到登錄頁面 request.getRequestDispatcher("/login.jsp").forward(request, response); } /** * @Method: removeAutoLoginCookie * @Description: 刪除自動登錄cookie， * JavaWeb中刪除cookie的方式就是新創建一個cookie，新創建的cookie與要刪除的cookie同名， * 設置新創建的cookie的cookie的有效期設置為0，有效路徑與要刪除的cookie的有效路徑相同 * @param request * @param response */ private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) { //創建一個名字為autologin的cookie Cookie cookie = new Cookie("autologin",""); //將cookie的有效期設置為0，命令瀏覽器刪除該cookie cookie.setMaxAge(0); //設置要刪除的cookie的path cookie.setPath(request.getContextPath()); response.addCookie(cookie); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}以上就是過濾器的幾個常見應用場景，希望對大家的學習有所幫助。
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