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

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 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>

转自:http://www.cnblogs.com/yqskj/articles/2226774.html