Java ServerSocketChannel SocketChannel（回调）

Question

我正在努力学习Java。 我想实现一个简单的网络连接4游戏以及聊天功能。

我希望我的网络逻辑能够无阻塞，所以经过多次研究后我发现SocketChannel是我重新考虑我需求之后的事情。

没有意义的是SocketChannels中缺少CallBack函数。就像在C＃中找到的一样。

我对这个时间的查询是：如何将收到的数据传递给聊天或游戏表单（JFrame）？

一些指导是最受欢迎的。

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，您需要使用选择器注册ServerSocketChannel：

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

然后你需要使用Selector来处理事件（你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);
}

肉将在doAccept（），doRead（）和doWrite（）中。 对于接受键，选择键将包含用于创建新Socket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);
}

最后一行向键添加了一些对象，以便从选择器接收的事件可以归因于连接（例如，它可能是游戏中的玩家）。 所以现在你可以接受新的连接，你只需要读写。

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();
}

类似的写作

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();
}

读取是相当简单的，您只需创建一个ByteBuffer，然后调用SocketChannels读取（ByteBuffer）（或其中一个变体），以便在通道上准备数据，直到它为空。

写入有点棘手，因为在收到写入事件之前，通常需要缓冲要写入的数据：

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，如果不是缓冲区中的所有数据都写入套接字，则需要适当的代码来管理类中的缓冲区（如果它已满），或者在写入暂挂方法中适当地修改缓冲区，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。