admin/admin.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>admin.html</title>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
	<font size="44">欢迎管理员光临</font>
  </body>
</html>

Filter.java


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;

//对敏感目录进行认证
public class FilterDemo6 implements Filter {
	public void init(FilterConfig filterConfig) throws ServletException {
	}
	public void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) throws IOException, ServletException {
		
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		
		//取得用户请求参数
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		
		//判段
		if(username!=null && password!=null){
			if(username.equals("admin") && password.equals("123")){
				//允许进入敏感资源
				chain.doFilter(request,response);
				
			}else{
				//转发到message.jsp页面
				request.setAttribute("message","用户名或密码不正确");
				request.getRequestDispatcher("/message.jsp").forward(request,response);
			}
		}else{
			//转发到message.jsp页面
			request.setAttribute("message","必须填入用户名和密码");
			request.getRequestDispatcher("/message.jsp").forward(request,response);
		}
	}
	public void destroy() {
	}
}

web.xml

<filter>
  	<filter-name>FilterDemo6</filter-name>
  	<filter-class>cn.web.filter.FilterDemo6</filter-class>
  </filter>
  <filter-mapping>
  	<filter-name>FilterDemo6</filter-name>
  	<url-pattern>/admin/*</url-pattern>
  </filter-mapping>

message.jsp

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page isELIgnored="false" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <body>
	${message} 	
  </body>
</html>