Java中filter用法完整代碼示例

本文研究的主要是Java中filter過濾器的相關用法，具體實現代碼如下。

filter過濾器主要使用於前台向後台傳遞數據是的過濾操作。程度很簡單就不說明了，直接給幾個已經寫好的代碼：

一、使瀏覽器不緩存頁面的過濾器

import javax.servlet.*;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * 用於的使Browser 不緩存頁面的過濾器*/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、檢測用戶是否登陸的過濾器

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、字符編碼的過濾器

import javax.servlet.*;import java.io.IOException;/** * 用於設置HTTP 請求字符編碼的過濾器，通過過濾器參數encoding指明使用何種字符編碼,用於處理Html Form請求參數的中文問題*/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、記錄用戶的訪問操作器

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 {//記錄用戶的訪問操作HttpServletRequest request1 = (HttpServletRequest)request;StringBuffer url = request1.getRequestURL();//對url進行過濾，如果是js/css/image則不進行處理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);}//保存到數據庫中saveToDb(userId,hostIp,sessionId,url.toString(),operTime,"");}// Pass control on to the next filterchain.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){//將報表任務數據保存到數據庫中Connection conn = null;Statement st = null;try {//構造sql表達式，將數據插入數據庫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;//表示操作失敗}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防止用戶訪問一些未被授權的資源

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方法的第一個參數為ServletRequest對象。此對像給過濾器提供了對進入的信息（包括表單數據、cookie和HTTP請求頭）的完全訪問。第二個參數為ServletResponse，通常在簡單的過濾器中忽略此參數。最後一個參數為FilterChain，此參數用來調用servlet或JSP頁。 HttpServletRequest request = (HttpServletRequest)servletRequest;//;//如果處理HTTP請求，並且需要訪問諸如getHeader或getCookies等在ServletRequest中無法得到的方法，就要把此request對象構造成HttpServletRequest HttpServletResponse response = (HttpServletResponse)servletResponse。 String currentURL = request.getRequestURI();//取得根目錄所對應的絕對路徑: String targetURL = currentURL.substring(currentURL.indexOf("/", 1), currentURL.length());//截取到當前文件名用於比較HttpSession session = request.getSession(false);if (!"/login.jsp".equals(targetURL)) {//判斷當前頁是否是重定向以後的登錄頁面頁面，如果是就不做session的判斷，防止出現死循環if (session == null || session.getAttribute("user") == null) {//*用戶登錄以後需手動添加session System.out.println("request.getContextPath()=" + request.getContextPath());response.sendRedirect(request.getContextPath() + "/login.jsp");//如果session為空表示用戶沒有登錄就重定向到login.jsp頁面return;}}//加入filter鏈繼續向下執行filterChain.doFilter(request, response);//.調用FilterChain對象的doFilter方法。 Filter接口的doFilter方法取一個FilterChain對像作為它的一個參數。在調用此對象的doFilter方法時，激活下一個相關的過濾器。如果沒有另一個過濾器與servlet或JSP頁面關聯，則servlet或JSP頁面被激活。 }public void init(FilterConfig filterConfig) throws ServletException {}}

html

 <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>//表示對所有jsp文件有效</filter-mapping>

總結

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