public static boolean isOnline(String hostname) { 
    try { 
      InetAddress ia; 
      boolean isonline = false; 
      ia = InetAddress.getByName(hostname);// 例如：www.baidu.com 
      isonline = ia.isReachable(1500); //超时时间1.5秒 
      return isonline; 
    } catch (UnknownHostException e) { 
      // TODO Auto-generated catch block 
      System.out.println("address:" + hostname + " is not unknown"); 
    } catch (IOException e) { 
      // TODO Auto-generated catch block 
      System.out.println("address:" + hostname + " is not reachable"); 
    } 
    return false; 
  } 

public static boolean isOnline(String hostname, int port) { 
    Socket server = null; 
    try { 
      server = new Socket(); 
      InetSocketAddress address = new InetSocketAddress(hostname, port);//例如 www.baidu.com 80 
      server.connect(address, 3000); 
      System.out.println("ok!"); 
      return true; 
    } 
    catch (UnknownHostException e) { 
      System.out.println("wrong!"); 
      e.printStackTrace(); 
    } catch (IOException e) { 
      System.out.println("wrong"); 
      e.printStackTrace(); 
    } 
    return false; 
  }