filter过滤器主要使用于前台向后台传递数据是的过滤操作。程度很简单就不说明了，直接给几个已经写好的代码：
一、使浏览器不缓存页面的过滤器
import javax.servlet.*; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class ForceNoCacheFilter implements Filter { public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException { ((HttpServletResponse) response).setHeader("Cache-Control","no-cache"); ((HttpServletResponse) response).setHeader("Pragma","no-cache"); ((HttpServletResponse) response).setDateHeader ("Expires", -1); filterChain.doFilter(request, response); } public void destroy() { } public void init(FilterConfig filterConfig) throws ServletException { } }
二、检测用户是否登陆的过滤器
import javax.servlet.*; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import java.util.List; import java.util.ArrayList; import java.util.StringTokenizer; import java.io.IOException; public class CheckLoginFilter implements Filter { protected FilterConfig filterConfig = null; private String redirectURL = null; private List notCheckURLList = new ArrayList(); private String sessionKey = null; public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) servletRequest; HttpServletResponse response = (HttpServletResponse) servletResponse; HttpSession session = request.getSession(); if(sessionKey == null) { filterChain.doFilter(request, response); return; } if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null) { response.sendRedirect(request.getContextPath() + redirectURL); return; } filterChain.doFilter(servletRequest, servletResponse); } public void destroy() { notCheckURLList.clear(); } private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) { String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo()); return notCheckURLList.contains(uri); } public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig = filterConfig; redirectURL = filterConfig.getInitParameter("redirectURL"); sessionKey = filterConfig.getInitParameter("checkSessionKey"); String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList"); if(notCheckURLListStr != null) { StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";"); notCheckURLList.clear(); while(st.hasMoreTokens()) { notCheckURLList.add(st.nextToken()); } } } }
三、字符编码的过滤器
import javax.servlet.*; import java.io.IOException; public class CharacterEncodingFilter implements Filter { protected FilterConfig filterConfig = null; protected String encoding = ""; public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { if(encoding != null) servletRequest.setCharacterEncoding(encoding); filterChain.doFilter(servletRequest, servletResponse); } public void destroy() { filterConfig = null; encoding = null; }
public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig = filterConfig; this.encoding = filterConfig.getInitParameter("encoding"); } }
四、记录用户的访问操作器
package com.qwserv.itm.pfl.log.svr; 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 java.text.SimpleDateFormat; import javax.servlet.http.HttpServletRequest; import com.qwserv.itm.api.pfl.sm.vo.Person; import java.sql.*; import com.qwserv.itm.api.ServiceAccess; import com.qwserv.itm.util.toolkit.DebugUtil; public class ObserveFilter implements Filter { protected static DebugUtil log = DebugUtil.getInstances("pfl-log", ObserveFilter.class); public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //记录用户的访问操作 HttpServletRequest request1 = (HttpServletRequest)request; StringBuffer url = request1.getRequestURL(); //对url进行过滤，如果是js/css/image则不进行处理 if (judgeFile(url.toString())){ String operTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new java.util.Date()); String hostIp = request.getRemoteAddr(); String sessionId = request1.getRequestedSessionId(); String userId = ""; Person person = (Person)request1.getSession().getAttribute("userObj"); if (null != person && null != person.getUser()){ userId = person.getUser().getId(); } String queryString = request1.getQueryString(); if (null != queryString) { url.append('?'); url.append(queryString); } //保存到数据库中 saveToDb(userId,hostIp,sessionId,url.toString(),operTime,""); } // Pass control on to the next filter chain.doFilter(request, response); } public void init(FilterConfig filterConfig) throws ServletException { } public boolean judgeFile(String url){ if (url.endsWith(".gif") || url.endsWith(".jpg") || url.endsWith(".png") || url.endsWith(".bmp") || url.endsWith(".css") || url.endsWith(".js") || url.endsWith(".jsx")){ return false; } else { return true; } } public int saveToDb(String userId, String hostIp,String sessionId,String url, String operTime,String desc){ //将报表任务数据保存到数据库中 Connection conn = null; Statement st = null; try { //构造sql表达式，将数据插入数据库 conn = ServiceAccess.getSystemSupportService().getDefaultConnection(); st = conn.createStatement(); String sql = "insert into LOG_OBSERVE_HISTORY(USERID,URL,Detail,SessionID,HostName,StartDate) values('"+ userId + "','" + url + "','" + desc + "','" + sessionId + "','" + hostIp + "','" + operTime + "')"; if (ServiceAccess.getSystemSupportService().getConnectionType(conn)==ServiceAccess.getSystemSupportService().JCA_TYPE_ORACLE){ sql = "insert into LOG_OBSERVE_HISTORY(Id,USERID,URL,Detail,SessionID,HostName,StartDate) values(LOG_OBSERVE_SEQ.nextval,'"+ userId + "','" + url + "','" + desc + "','" + sessionId + "','" + hostIp + "',TO_DATE('" + operTime + "','YYYY-MM-DD HH24:MI:SS'))"; } st.executeUpdate(sql); } catch (Exception e) { e.printStackTrace(); log.error("--------------------The url String is:" + url + "-------------------------------"); return 1; //表示操作失败 } finally { if (null != st) { try{ st.close(); } catch(Exception e) { e.printStackTrace(); } st = null; } if (conn != null) { try { conn.close(); } catch (Exception e) { e.printStackTrace(); } conn = null; } } return 0; //表示操作成功 } }
<filter> <filter-name>ObserveFilter</filter-name> <filter-class>com.qwserv.itm.pfl.log.svr.ObserveFilter</filter-class> </filter> <filter-mapping> <filter-name>ObserveFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
五.Filter防止用户访问一些未被授权的资源
package com.drp.util.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; import javax.servlet.http.HttpSession; public class AuthFilter implements Filter { public void destroy() { } public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { //1,doFilter方法的第一个参数为ServletRequest对象。此对象给过滤器提供了对进入的信息（包括表单数据、cookie和HTTP请求头）的完全访问。 //第二个参数为ServletResponse，通常在简单的过滤器中忽略此参数。最后一个参数为FilterChain，此参数用来调用servlet或JSP页。 HttpServletRequest request = (HttpServletRequest)servletRequest;//如果处理HTTP请求，并且需要访问诸如getHeader或getCookies等在ServletRequest中无法得到的方法，就要把此request对象构造成HttpServletRequest HttpServletResponse response = (HttpServletResponse)servletResponse。 String currentURL = request.getRequestURI();//取得根目录所对应的绝对路径: String targetURL = currentURL.substring(currentURL.indexOf("/", 1), currentURL.length()); //截取到当前文件名用于比较 HttpSession session = request.getSession(false); if (!"/login.jsp".equals(targetURL)) {//判断当前页是否是重定向以后的登录页面页面，如果是就不做session的判断，防止出现死循环 if (session == null || session.getAttribute("user") == null) {//*用户登录以后需手动添加session System.out.println("request.getContextPath()=" + request.getContextPath()); response.sendRedirect(request.getContextPath() + "/login.jsp");//如果session为空表示用户没有登录就重定向到login.jsp页面 return; } } //加入filter链继续向下执行 filterChain.doFilter(request, response);//.调用FilterChain对象的doFilter方法。Filter接口的doFilter方法取一个FilterChain对象作为它的一个参数。在调用此对象的doFilter方法时，激活下一个相关的过滤器。如果没有另一个过滤器与servlet或JSP页面关联，则servlet或JSP页面被激活。 } public void init(FilterConfig filterConfig) throws ServletException { } }
<filter> <filter-name>AuthFilter</filter-name> <filter-class>com.drp.util.filter.AuthFilter</filter-class> </filter> <filter-mapping> <filter-name>AuthFilter</filter-name> <url-pattern>*.jsp</url-pattern> <!--表示对所有jsp文件有效--> </filter-mapping>