SessionFilter.java

package com.base.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;

import com.base.constants.SessionKeyConstants;
import com.mvc.entity.User;

public class SessionFilter implements Filter {

	public void destroy() {
		// 过滤器销毁，一般是释放资源
	}

	/**
	 * 某些url需要登陆才能访问（session验证过滤器）
	 */
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) arg0;
		HttpServletResponse response = (HttpServletResponse) arg1;
		HttpSession session = request.getSession();
		if ((User) session.getAttribute(SessionKeyConstants.LOGIN) == null) {
			String errors = "您还没有登录，或者session已过期。请先登陆!";
			request.setAttribute("Message", errors);
			request.getRequestDispatcher("/jsp/login.jsp").forward(request, response);
		} else {
			arg2.doFilter(request, response);
		}
	}

	public void init(FilterConfig arg0) throws ServletException {
		// 初始化操作，读取web.xml中过滤器配置的初始化参数，满足你提的要求不用此方法
	}
}