public class NioBlockingEchoServer {

   public static void main(String[] args) throws IOException {
       ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
       serverSocketChannel.bind(new InetSocketAddress("localhost", 7000));

       while (active) {
           SocketChannel socketChannel = serverSocketChannel.accept(); // blocking

           ByteBuffer buffer = ByteBuffer.allocate(1024);
           while (true) {
               buffer.clear();
               int read = socketChannel.read(buffer); // blocking
               if (read < 0) {
                   break;
               }

               buffer.flip();
               socketChannel.write(buffer); // blocking
           }

           socketChannel.close();
       }

       serverSocketChannel.close();
   }
}