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  1. Busy Wait Eventloop Echo Server - implementation of echo server that is looping infinitely while trying to get data from socket.
  2. Selector Eventloop Echo Server - implementation of echo server utilizing NioChannelEventHandler.


To run the examples in an IDE, you need to clone DataKernel locally and import it as a Maven project. Then you should set up default working directory of run configurations in your IDE so that the examples can work correctly. In accordance to DataKernel module structure, the working directory should be set to the module folder.

In IntelliJ IDEA you can do it in the following way: Run -> Edit configurations -> |Run/Debug Configurations -> |Templates -> Application| -> |Working directory -> $MODULE_WORKING_DIR$||.

Before running the examples, build the project (Ctrl + F9 for IntelliJ IDEA).

Then open one of the classes:

  • BusyWaitEventloopEchoServer
  • SelectorEventloopEchoServer

which are located at datakernel -> examples -> eventloop and run main() of the chosen example.

After you launch any of the servers, enter this command in console:

telnet localhost 22233

You've just connected to the echo server and can interact with it, try to write some messages. To close the connection, press Ctrl+5 and then type close.


Both of the examples utilize eventloop.listen() as the basis of server processing. This method creates ServerSocketChannel that listens on InetSocketAddress.

Also, they both utilize ByteBuf module to efficiently wrap incoming and outgoing messages.

But servers have different approaches towards AcceptCallback interface implementation. AcceptCallback is called when new incoming connection is being accepted. BusyWaitEventloopEchoServer simply uses an infinite while loop which processes all of the connections:

while (true) {
	int read =;
    if (read == 0) {
    } else if (read == -1) {
    String message = StandardCharsets.UTF_8.decode((ByteBuffer) bufferIn.flip()).toString();
    System.out.printf("Received message from client(%s): %s", clientAddress, message);
    String stringIn = "Server: " + message;

Selector Eventloop Echo Server implements NioChannelEventHandler interface which has onReadReady() and onWriteReady() methods that respectively read incoming messages from clients and send a response.

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