如何在Java（TelNet）中实现接收套接字的事件？

Question

I'm doing an application in NetBeans (Java) to open a socket (Client) and exchange information with it.

The way I'm doing this is as follows:

final String HOST = "10.1.1.98";//"localhost";

final int PORT=1236;

Socket sc;

DataOutputStream message;

public void initClient()
{
    try
{
        sc = new Socket( HOST , PORT );
        message = new DataOutputStream(sc.getOutputStream());

    }
    catch(Exception e )
    {
        System.out.println("Error: "+e.getMessage());
    }
}

I must know if the server sends information constantly. One way would be to use a timer that constantly run the following piece of code:

message = new DataOutputStream(sc.getOutputStream());

But it isn't efficient.

I want to create an event to be in charge of acquiring data from the server, for example in C# I used EventHandler:

ip = new TcpIp(ipAddress, port);

ip.DataRead += new EventHandler<TramaEventArgs>(ip_DataRead);

....

void ip_DataRead(object sender, TramaEventArgs e) 
{

}

How I can do this in Java?

Answer 1

The 'correct' way to do non-blocking IO in Java is to use the NIO API, look in particular at java.nio.channels.AsynchronousSocketChannel that allows you to write code like this:

InetSocketAddress serverAddress = new InetSocketAddress(InetAddress.getByName("10.1.1.98"), 1236);

AsynchronousSocketChannel clientSocketChannel = AsynchronousSocketChannel.open();
clientSocketChannel.connect(hostAddress).get();

ByteBuffer buffer = getBuffer();
clientSocketChannel.read(buffer, Void, new ReadHandler(buffer));

Where the handler looks like this:

public class ReadHandler implements CompletionHandler<Integer, Void>
{
  private ByteBuffer buffer;

  public ReadHandler(ByteBuffer buffer)
  {
    this.buffer = buffer;
  }

  public void completed(Integer read, Void attachment) 
  {
    if (read < 0)
    {
      return;
    }

    //TODO: read buffer according to the number of bytes read and process accordingly.
  }

  public void failed(Throwable exc, Void attachment)  
  {
    //TODO: handle exception.
  }
}

The important things to note here are:

• it's possible you'll be reading incomplete messages and so you need to handle that.
• you should do as little processing as possible in the ReadHandler , instead passing each complete message off (maybe to an ExecutorService or some internal queue depending on your requirements).