Java ServerSocketChannel SocketChannel (callback)

Question

I am trying to learn Java. I would like to implement a simple network game with 4 connection, as well as a chat function.

I want my network logic not to block, so after much research, I found that SocketChannel is what I am after fixing my needs.

What else does not make sense is the lack of CallBack features in SocketChannels. Like in C #.

My request this time: How can I deliver data received in the form of a chat or a game (JFrame)?

Some recommendations are welcome.

Answer 1

You need to use a selector. First create a selector to receive events:

Selector selector = Selector.open()

ServerSocketChannel :

SelectionKey acceptKey = server.register(selector, SelectionKey.OP_ACCEPT);

( " " :

while(true){
  //how many channel keys are available
  int available = selector.select(); 
  //select is blocking, but should only return if available is >0, this is more of a sanity check
  if(available == 0) continue;

  Iterator<SelectionKey> keys = selector.selectedKeys().iterator();
  while(keys.hasNext()){
    SelectionKey key = keys.next();
    keys.remove();
    //someone is trying to connect to the server socket
    if(key.isAcceptable())  doAccept(key); 
    //someone is sending us data
    else if(key.isReadable()) doRead(key); 
    //we are trying to (and can) send data
    else if(key.isWritable()) doWrite(key);
}

doAccept(), doRead() doWrite(). accept Socket.

doAccept(SelectionKey key){

//create the new socket
SocketChannel socket = ((ServerSocketChannel)key.channel()).accept(); 
//make it non-blocking as well
socket.configureBlocking(false);

...
//here you would likely have some code to init your game objects / communication protocol, etc. and generate an identifier object (used below).
//and be able to find the socket created above
...

//Since it is non blocking it needs a selector as well, and we register for both read and write events
SelectionKey socketKey = socket.register(selector, SelectionKey.OP_READ|SelectionKey.OP_WRITE);
// so we can identify the events as they come in
socketKey.attach(someSocketIndentifier);
}

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doRead(SelectionKey key){
  //here we retrieve the key we attached earlier, so we now what to do / wheer the data is coming from
  MyIdentifierType myIdentifier = (MyIdentifierType)key.attachment();
  //This is then used to get back to the SocketChannel and Read the Data
  myIdentifier.readTheData();
}

doWrite(SelectionKey key){
  //here we retrieve the key we attached earlier, so we now what to do / wheer the data is coming from
  MyIdentifierType myIdentifier = (MyIdentifierType)key.attachment();
  //This is then used to get back to the SocketChannel and Read the Data
  myIdentifier.getSocketHandler().writePendingData();
}

, ByteBuffer, SocketChannels read (ByteBuffer) ( ), .

, , , , :

class MyNetworkClass{
  ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
  SocketChannel commchannel; //from the server accept processing

  ...

  public void write(byte[] data){
    //here the class writeBuffer object is filled with the data
    //but it isn't actually sent over the socket
    ...
  }

  public void writePendingData(){
    //here actually write the data to the socket
    commchannel.write(writeBuffer);
  }
}

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