private static Socket createClientSocket(String serverIpAddress,
			int serverPort) {
		Socket clientSocket = null;
		try {
			clientSocket = new Socket(serverIpAddress, serverPort);
			log.info("create client socket");
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			log.severe("create client socket: fail UnknownHostException");
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			log.severe("create client socket: fail IOException");
		}
		return clientSocket;
	}