JAVA的HTTP请求的问题

Question

 String url="http://www.baidu.com/"; 
      String get="";
      int code=0;
      try{  
       get = "email=" + URLEncoder.encode("e-mail", "UTF-8")    + "&password=" + "password";
            URL l_url = new java.net.URL(url);
            HttpURLConnection l_connection = (java.net.HttpURLConnection) l_url.openConnection();
           
            l_connection.setRequestProperty("Connection","aaa");
            l_connection.setRequestProperty("User-Agent","123");
            l_connection.connect();
            l_connection = (HttpURLConnection) l_url.openConnection ();
            l_connection.setFollowRedirects(true);
            l_connection.setInstanceFollowRedirects(true);
            l_connection.setAllowUserInteraction(true);
            l_connection.setUseCaches(true);
            l_connection.setRequestMethod("GET");
        l_connection.usingProxy();
        l_connection.setDoInput(true);
            code = l_connection.getResponseCode();
            System.out.println("~~~~~"+code);
            String headName,headValue;
            for (int i = 0; (headValue = l_connection.getHeaderField(i)) != null; i++) {
                headName = l_connection.getHeaderFieldKey(i);
                if (headValue!=null)
                System.out.println("headRetParam:"+l_connection.getHeaderFieldKey(i)+" = " +headValue);
            }
            l_connection.disconnect();
            l_connection = null;
            l_url = null;    
###########################################################################
为什么 l_connection.setRequestProperty("Connection","aaa");
这样设置，但是在返回的信息头部取的时候却没有Connection这项参数呢？

Answer 1

l_connection.setRequestProperty("Connection","aaa");
l_connection.setRequestProperty("User-Agent","123");是你写给baidu的，baidu不会再返回给你吧。