package com.jykj.comutils;

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 LoginFilter implements Filter{

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)
			throws IOException, ServletException {
		// TODO Auto-generated method stub
		HttpServletRequest request = (HttpServletRequest)servletrequest;
		HttpServletResponse response = (HttpServletResponse)servletresponse;
		String requestURI = request.getRequestURI();
		String contextPath = request.getContextPath();
		//去除项目名时访问的当前路径
		String url = requestURI.substring(contextPath.length());
		HttpSession session = request.getSession(false);
		if (url.indexOf("index.jsp")>0||url.equals("/")||url.indexOf("image.html")>0||url.indexOf("notice.jsp")>0||url.indexOf("educational.jsp")>0) {//登陆页面放过
			filterchain.doFilter(request, response);
		}else {//不是登陆页面，进行判定session
			if (session==null||session.getAttribute("user")==null) {
				response.sendRedirect("/");
			}else {
				filterchain.doFilter(request,response);
				return;
			}
		}
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}

web.xml配置

<filter>
    <filter-name>LoginFilter</filter-name>
    <filter-class>com.jykj.comutils.LoginFilter</filter-class>
  </filter>
 
  <filter-mapping>
    <filter-name>LoginFilter</filter-name>
    <url-pattern>*.htm</url-pattern>
  </filter-mapping>