从网络服务器同步系统时间，采用UDP协议，使用DatagramPacket，DatagramSocket类-From the network server time synchronization system, using UDP protocol, use the DatagramPacket, DatagramSocket Class

实现同步网络时间，并修改本机时间为正确网络时间，时间误差不超过一秒-Network time synchronization, and modify the local time to the correct network time, the time error of less than a second