TCP(Transmission Control Protocol)
传输控制协议，是一种面向连接的，可靠的，基于字节流的传输层通信协议，TCP层位于IP层之上，应用层之下的中间层。TCP保障了两个应用程序之间的可靠通信。通常用于互联网协议，被称为TCP / IP

UDP(User Datagram Protocol)
用户数据报协议，位于OSI模型的传输层。一个无连接的协议。提供了应用程序之间要发送数据的数据报。由于UDP缺乏可靠性且属于无连接协议，所以应用程序通信必须容许一些丢失，错误或重复的数据包

DatagramPacket 类(UDP)

服务端

public class Socket_S {

    public static void main(String[] args) throws IOException {

        DatagramSocket datagramSocket = new DatagramSocket(6666);

        DatagramPacket datagramPacket = new DatagramPacket(new byte[1024*8],8192);

        datagramSocket.receive(datagramPacket);

        byte[] data = datagramPacket.getData();

        int length = datagramPacket.getLength();

        String str = new String(data,0,length);

        System.out.println(str);
    }
}

客户端

public class Socket_B {

    public static void main(String[] args) throws IOException {

        //建立数据起始
        DatagramSocket datagramSocket = new DatagramSocket(9999);

        String msg = "hello world";
        DatagramPacket datagramPacket = new DatagramPacket(msg.getBytes(StandardCharsets.UTF_8), 
                                                           msg.getBytes(StandardCharsets.UTF_8).length, 
                                                           InetAddress.getByName("127.0.0.1"),6666);

        datagramSocket.send(datagramPacket);
    }
}

Socket类 和 ServerSocket(TCP)

服务器应用程序通过使用 java.net.ServerSocket 类以获取一个端口,并且侦听客户端请求

服务器端

public class Server_ {

    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = new ServerSocket(9999);

        Socket socket = serverSocket.accept();

        InputStream inputStream = socket.getInputStream();

        File file = new File("F:\\map.txt");

        FileOutputStream fileOutputStream = new FileOutputStream(file);

        byte[] bytes = new byte[1024];

        int len = 0;

        while ((len = inputStream.read(bytes)) != -1){

            fileOutputStream.write(bytes,0,len);
        }

        serverSocket.close();
    }
}

客户端

public class Client_ {

    public static void main(String[] args) throws IOException {

        String adr = "127.0.0.1";

        int port = 9999;

        File file = new File("F:/map.txt");

        FileInputStream fileInputStream = new FileInputStream(file);

        Socket socket = new Socket(adr,port);

        byte[] bytes = new byte[1024];

        int len = 0;

        OutputStream outputStream = socket.getOutputStream();

        while ((len = fileInputStream.read(bytes)) != -1){

            outputStream.write(bytes,0,len);
        }

        socket.shutdownOutput();
    }
}