html代码
分别是一个登录界面和登录成功的界面

	


	
欢迎进入我的网站
	

		

		账号

		密码

		提交
		
	
	

欢迎来到我的网站

web.xml的配置

    
      test
  exercise2.test
  
  
  	test
  	/test
  
    
  		test_filter
  		exercise2.test_filter
  
 	
 		test_filter
 		/web.html
 	  

java代码，只要实现登录时的响应和filter

package exercise2;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class test extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
	// TODO Auto-generated method stub
	System.out.println("经过了set程序");
	String name=req.getParameter("t1");
	System.out.println("账号:"+name);
	if("admin".equals(name)) {
	System.out.println("密码正确");
	req.getSession().setAttribute("user", name);
	req.getRequestDispatcher("/web.html").forward(req, resp);}
	else {
		resp.getWriter().write("login fail");
	}
}
}

package exercise2;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class test_filter implements Filter{

	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		// TODO Auto-generated method stub
		HttpServletRequest httpServletRequest=(HttpServletRequest)arg0;
		Object use=httpServletRequest.getSession().getAttribute("user");
		if(use==null) {
			System.out.println("调用过滤器:登录失败");
			arg0.getRequestDispatcher("/index.html").forward(arg0, arg1);
		}else {
			System.out.println("调用过滤器:成功登录");
			arg2.doFilter(arg0, arg1);
		}
	}
}

主要还是说明一下web.xml的filter过滤器的配置，

	test_filter
	/web.html

这里第三行代码实际代表的过滤的网站，过滤规则为
http://id/工程路径/你过滤的位置；
我这里代表的是 http://localhost:8080/exercise2/web.html；
还有几个比较方便的过滤方法
/*表示所有
*.html对所有html过滤