src/com/inloam/common/UrlFilter.java

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package com.inloam.common;

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 org.apache.commons.lang.StringUtils;


public class UrlFilter  implements Filter{
	
	/**
	 * @param args
	 */
	public void destroy() {

	}

	public void doFilter(ServletRequest servletRequest,
			ServletResponse servletResponse, FilterChain filterChain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) servletRequest;
		HttpServletResponse response = (HttpServletResponse) servletResponse;
		boolean bool = true;
		
		String username = (String) request.getSession().getAttribute("username");
		if(StringUtils.isEmpty(username)){
			bool = false;
		}

        if(bool){
			filterChain.doFilter(request, response);
        }else{
//        	response.sendRedirect("admin.do");
            String ss = "<script>alert('您没有权限访问！');</script>";
	        try {
				response.setContentType("text/plain;charset=UTF-8");
				response.getWriter().write(ss);
	
			} catch (IOException e) {
	            e.printStackTrace();
			}
        }
	}

	public void init(FilterConfig filterConfig) throws ServletException {

	}

}