Filter 过滤器深究

      Servlet过滤器的核心：
      1.在web.xml中配置Filter所对应的java类
      2.实现javax.servlet.Filter接口的类
      3.实现Filter接口中的方法,即init方法，并进行初始化
      4.实现doFilter方法，完成对过滤器的请求和响应
      5调用FilterChain接口对象的doFilter方法，像后续过滤器进行传递请求或者跳转到响应的页面

    filter过滤器主要使用于前台向后台传递数据是的过滤操作。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
Java代码
 import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class MyFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException
 {
  ((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 SetCharacterEncodingFilter implements Filter { 
     
    private FilterConfig filterConfig; 
 
     public void init(FilterConfig filterConfig) throws ServletException { 
         this.filterConfig = filterConfig; 
     } 
 
     //Process the request/response pair 
     public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) { 
         try { 
             request.setCharacterEncoding("utf-8"); 
             response.setCharacterEncoding("utf-8"); 
             filterChain.doFilter(request, response);  
             HttpServletRequest ser =(HttpServletRequest) request;
             HttpServletResponse seo = (HttpServletResponse) response;
             //获得跳转的路径,即可知道跳转的路径

             System.out.println(ser.getRequestURL());
         } catch (ServletException sx) { 
             filterConfig.getServletContext().log(sx.getMessage()); 
         } catch (IOException iox) { 
             filterConfig.getServletContext().log(iox.getMessage()); 
         } 
     } 
 
     //Clean up resources 
     public void destroy() { 
     } 
 
}  
 
四、记录用户的访问操作器
package com.mymd.filter;
import java.io.IOException;
import javax.servlet.*;
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 VisitFilter implements Filter {
    protected static DebugUtil log = DebugUtil.getInstances("pfl-log", VisitFilter.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_Visit_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_Visit_HISTORY(Id,USERID,URL,Detail,SessionID,HostName,StartDate)  values(LOG_Visit_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>VisitFilter</filter-name>
        <filter-class>com.mymd.filter.VisitFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>VisitFilter</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.mymd.filter;   
import java.io.IOException;   
import javax.servlet.*;    
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:   就是我们浏览器中所显示的路径
     
  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.mymd.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>