Java中filter用法完整代码示例

本文研究的主要是Java中filter过滤器的相关用法，具体实现代码如下。

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;/** * 用于的使 Browser 不缓存页面的过滤器 */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、检测用户是否登陆的过滤器

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、字符编码的过滤器

import javax.servlet.*;import java.io.IOException;/**  * 用于设置 HTTP 请求字符编码的过滤器，通过过滤器参数encoding指明使用何种字符编码,用于处理Html Form请求参数的中文问题  */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 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){//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 {}}

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>//表示对所有jsp文件有效</filter-mapping>

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