手撸实现UDP和TCP通信

UDP

UDP是一种面向无连接的协议，因此传输过程中不能保证数据的完整性。jdk提供了网络通信包，在java.net包下提供了两个类DatagramPacket和DatagramSocket来实现UDP通信。这两个类可以这样理解，DatagramSocket是路，DatagramPacket路上装有人的车。也就是DatagramSocket决定了通信目标，DatagramPacket则代表封装好的数据。

UDP的特性决定了UDP协议的应用场景，在我身边最常见的应用场景就是物联网设备与服务端的通信。

UDPClient实现

public class UDPClient {
    public static void main(String[] args) throws Exception {
           byte[] data = "我是客户端，我发送了一条消息".getBytes();
        InetAddress address = InetAddress.getByName("localhost");
        DatagramPacket packet = new DatagramPacket(data,data.length,address,8888);
        DatagramSocket socket = new DatagramSocket();
        socket.send(packet);

        byte[] message = new byte[1024];
        DatagramPacket packet1 = new DatagramPacket(message,message.length);
        socket.receive(packet1);
        String replyContent = new String(message,0,message.length);
        System.out.println("UDPClient 接收到了消息："+replyContent);
        socket.close();
    }
}

UDPServer实现

public class UDPServer {
    public static void main(String[] args) throws Exception {
         DatagramSocket socket = new DatagramSocket(8888);
        byte[] data = new byte[1024];
        DatagramPacket packet = new DatagramPacket(data,data.length);
        socket.receive(packet);
        String message = new String(data,0,packet.getLength());
        System.out.println("UDPServer 接收到了消息："+message);

        InetAddress address = packet.getAddress();
        int port = packet.getPort();
        byte[] replyContent = "我是服务端，我回复了一条消息".getBytes();
        DatagramPacket packet1 = new DatagramPacket(replyContent, replyContent.length, address, port);
        socket.send(packet1);
        socket.close();
    }
}

TCP

TCP是一种面向连接的服务，经过三次握手建立连接，通过传输字节流的方式进行通信。因此可以保证消息的完整性。同样，在java.net包下也提供了两个包Socket和ServerSocket来实现TCP通信。

TCPClient

public class TCPClient {

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

        Socket socket = new Socket("localhost",8081);
        DataOutputStream out = new DataOutputStream(socket.getOutputStream());
        String data = "我是客户端，我发了一条消息";
        out.writeUTF(data);

        DataInputStream in = new DataInputStream(socket.getInputStream());
        String message = in.readUTF();
        System.out.println("TCPClient："+message);
        socket.close();
    }
}

TCPServer

public class TCPServer {

    public static void main(String[] args) throws Exception{
        ServerSocket serverSocket = new ServerSocket(8081);
        Socket socket = serverSocket.accept();
        DataInputStream in = new DataInputStream(socket.getInputStream());
        String message = in.readUTF();
        System.out.println("TCPServer："+message);

        DataOutputStream out = new DataOutputStream(socket.getOutputStream());
        out.writeUTF("我是服务器，我回复了一条消息");
        socket.close();
        serverSocket.close();
    }
}