Java ServerSocketChannel SocketChannel(回调)

Question

我正在努力学习 Java。我想实现一个简单的联网 connect 4 游戏以及聊天功能。

我希望我的网络逻辑是非阻塞的，所以经过大量研究后，我发现 SocketChannel 正是我重新调整需求后的样子。

仍然没有意义的是 SocketChannels 中缺少回调函数。就像在 C# 中发现的那样。

我这次的问题是:如何将接收到的数据传递给聊天或游戏窗体(JFrame)？

欢迎提供一些指导。

Answer 1

您需要使用选择器。首先创建一个 Selector 来接收事件:

Selector selector = Selector.open()

然后需要向选择器注册ServerSocketChannel:

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

然后您需要使用 Selector 在事件传入时对其进行处理(您可以将其视为流程的“回调”部分:

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);
}

关键在于 doAccept()、doRead() 和 doWrite()。对于接受键，选择键将包含创建新套接字的信息。

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);
}

最后一行向键添加一些对象，以便从选择器接收到的事件可以归因于连接(例如，它可能是您游戏中的玩家)。所以现在您可以接受新的连接，您只需要读取和写入。

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();
}

类似地写

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();
}

读取非常简单，您只需创建一个 ByteBuffer，然后调用 SocketChannels read(ByteBuffer)(或其变体之一)以在 channel 上准备好数据，直到它为空。

写入有点棘手，因为您通常希望缓冲要写入的数据，直到收到写入事件:

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);
  }
}

请注意，如果缓冲区已满，您将需要适当的代码来管理类中的缓冲区，或者如果缓冲区中的所有数据并未写入套接字，则需要在写入挂起方法中对其进行适当修改，以及在此过程中可能抛出的各种异常。希望这有助于您入门。