FileReceiver.java

final class FileReceiver {
 
    private final int port;
    private final FileWriter fileWriter;
    private final long size;
 
    FileReceiver(final int port, final FileWriter fileWriter, final long size) {
        this.port = port;
        this.fileWriter = fileWriter;
        this.size = size;
    }
 
    void receive() throws IOException {
        SocketChannel channel = null;
 
        try (final ServerSocketChannel serverSocketChannel = ServerSocketChannel.open()) {
            init(serverSocketChannel);
 
            channel = serverSocketChannel.accept();
 
            doTransfer(channel);
        } finally {
            if (!Objects.isNull(channel)) {
                channel.close();
            }
 
            this.fileWriter.close();
        }
    }
 
    private void doTransfer(final SocketChannel channel) throws IOException {
        assert !Objects.isNull(channel);
 
        this.fileWriter.transfer(channel, this.size);
    }
 
    private void init(final ServerSocketChannel serverSocketChannel) throws IOException {
        assert !Objects.isNull(serverSocketChannel);
 
        serverSocketChannel.bind(new InetSocketAddress(this.port));
    }
}