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 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 {
	}
}

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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