java中filter的用法

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

Java代码 

 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

 

1. import javax.servlet.*;
2. 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;
• /**
• * 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面<p>
• * 配置参数<p>
• * checkSessionKey 需检查的在 Session 中保存的关键字<br/>
• * redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath<br/>
• * notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath<br/>
• */
• 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

1. import javax.servlet.*;
2. import java.io.IOException;
3. /**
4. * 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
5. */
6. public class CharacterEncodingFilter
7. implements Filter
8. {
9. protected FilterConfig filterConfig = null;
10. protected String encoding = "";
11. public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
12. {
13. if(encoding != null)
14. servletRequest.setCharacterEncoding(encoding);
15. filterChain.doFilter(servletRequest, servletResponse);
16. }
17. public void destroy()
18. {
19. filterConfig = null;
20. encoding = null;
21. }
22. public void init(FilterConfig filterConfig) throws ServletException
23. {
24. this.filterConfig = filterConfig;
25. this.encoding = filterConfig.getInitParameter("encoding");
26. }
27. }

四、记录用户的访问操作器

代码：
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

1. 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>