Java中的Filter

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>