BlockingServer.java

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.channels.ServerSocketChannel;

public class BlockingServer {
    public static void main(String[] args) throws IOException {
        run();
    }

    static void run() throws IOException {
        final ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        final ServerSocket socket = serverSocketChannel.socket();
        final InetSocketAddress inetSocketAddress = new InetSocketAddress(5556);
        socket.setReuseAddress(true);
        socket.bind(inetSocketAddress);
        while (true) {
            final Socket client = socket.accept();
            // each connection use 1 thread.
            new Thread(() -> {
                try (client) {
                    byte[] buf = new byte[1024];
                    System.out.println(">>>client.isClosed():" + client.isClosed());
                    while (!client.isClosed()) {
                        final int read = client.getInputStream().read(buf);
                        if (read > 0) {
                            client.getOutputStream().write(buf, 0, read);
                        } else {
                            client.close();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
                System.out.println("Closed connection.");
            }).start();
        }
    }
}