filter阻止在地址欄直接輸入shervlet地址進行的操作

package edu.sanyang.hr.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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebFilter("/*")
public class ServletFilter implements Filter {

	public void destroy() {
	}

	public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
			HttpServletRequest request = (HttpServletRequest) req;
			HttpServletResponse response = (HttpServletResponse) resp;
		    String referer = request.getHeader("referer");
		    //獲得用戶請求的參數
			String path = request.getQueryString();
	        if (referer == null && (path + "a").contains("action")) {
	        	response.sendRedirect("404.html");
	        	 return;
			}
		chain.doFilter(request, response);
	}

	public void init(FilterConfig fConfig) throws ServletException {
	}

}