最近在做一個專案，用到了web的過濾器，與大家分享下：

webxml中需要配置：<pre name="code" class="html"><!-- 登入攔截 -->
	<filter>
		<filter-name>LoginInterceptor</filter-name>
		<filter-class>com.yc.vcloud.utils.LoginInterceptor</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>LoginInterceptor</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
 

Java原始碼

package com.yc.vcloud.utils;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.filter.OncePerRequestFilter;

/**
 * 登入過濾
 * 
 * @author Luo_dawei
 *
 */
public class LoginInterceptor extends OncePerRequestFilter {
	@Override
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {
		// 不過濾的uri
		String[] notFilter = new String[] { "login.jsp", "back/backlogin.jsp", "index.html", "register.jsp" };
		// 請求的uri
		String uri = request.getRequestURI();
		// uri中包含page時才進行過濾
		if (uri.contains("page")) {
			// 是否過濾
			boolean doFilter = true;
			for (String s : notFilter) {
				if (uri.contains(s)) {
					// 如果uri中包含不過濾的uri，則不進行過濾
					doFilter = false;
					break;
				}
			}
			System.out.println("doFilter==>"+doFilter);
			if (doFilter) {
				// 執行過濾
				// 從session中獲取登入者實體
				Object objUser = request.getSession().getAttribute(SessionAttribute.USERLOGIN);
				Object objAdmin = request.getSession().getAttribute(SessionAttribute.ADMINLOGIN);
				if (null == objUser) {
					// 如果session中不存在登入者實體，則彈出框提示重新登入
					// 設定request和response的字符集，防止亂碼
					request.setCharacterEncoding("UTF-8");
					response.setCharacterEncoding("UTF-8");
					response.setContentType("text/html;charset=utf-8");
					PrintWriter out = response.getWriter();
					StringBuilder builder = new StringBuilder();
					builder.append("<script type=\"text/javascript\">");
					builder.append("alert('您好,請先登入!');");
					if (null == objUser) {
						builder.append("location.href='login.jsp';");
					}
					if (null == objAdmin) {
						builder.append("location.href='backlogin.jsp';");
					}
					builder.append("</script>");
					out.print(builder.toString());
				} else {
					// 如果session中存在登入者實體，則繼續
					filterChain.doFilter(request, response);
				}
			} else {
				// 如果不執行過濾，則繼續
				filterChain.doFilter(request, response);
			}
		} else {
			// 如果uri中不包含page，則繼續
			filterChain.doFilter(request, response);
		}
	}
}