Re: Retrieving Sender Information From A Non-blocking DatagramChannel

From:
Bala <r.balaji.iyer@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 24 Oct 2011 14:42:15 -0700 (PDT)
Message-ID:
<0371aeff-32b2-4448-b71b-e91178f4cf38@f16g2000yqk.googlegroups.com>
On Oct 24, 4:41 pm, Robert Klemme <shortcut...@googlemail.com> wrote:

On 24.10.2011 21:14, Bala wrote:

I have a DatagramChannel that I have added to a Java Selector. Hence
the configureblocking is set to false since the selector expects a non
blockign socket.
I have to use the DatagramChannel's receive call and cannot use the
socket.receive which reads the data in a packet due to the nonblocking
mode.

If I would have received / sent DatagramPacket using the
dc.socket().receive call, then the packet provides you the Sender
information anyways.

The problem is that I need the host/port of the sender from this
DatagramChannel. I see there are a couple of private variables withi=

n

the DatagramChannel class cachedSenderInetAddress, cachedSenderPort)
that have this information but those are private variables and I do
not see any method in the DatagramChannel or its socket to retrieve
the sender information.

Is there a way I can do this?

Here is the code snippet for the Receiver
========================

==================

class CReadDatagramChannel {

   DatagramChannel dc = DatagramChannel.open().configureBlocking(=

false);

   public CReadDatagramChannel (int port, Selector selector) {
           dc.socket().setReuseAddress(true);
           dc.socket().bind(new InetSocketAddress(port));
           dc.register(selector, SelectionKey.OP_READ, this=

);

   }

   /* This method gets invoked from the Selector on the isReadable(=

) */

   public void processRead () {
           // I cannot do dc.socket().receive(packet) since=

 the blocking is

false.
           ByteBuffer socketBuffer = ByteBuffer.allocate(=

1024);

           dc.receive (socketBuffer);


You're almost there:

"Returns:
The datagram's source address, or null if this channel is in
non-blocking mode and no datagram was immediately available"

http://download.oracle.com/javase/6/docs/api/java/nio/channels/Datagr...)

In other words: you just need to change the line into

final SocketAddress sender = dc.receive(socketBuffer);

and be done.

   }
}

Here is the code snippet for the Sender
========================

================

class CWriteDatagramChannel {
   DatagramChannel dc = DatagramChannel.open().configureBlocking(=

false);

   public CWriteDatagramChannel (int port, Selector selector) {
           dc.socket().setReuseAddress(true);
           dc.socket().bind(new InetSocketAddress(port));
           dc.register(selector, SelectionKey.OP_READ, this=

);

   }

   /* This method gets invoked from the Selector on the isWritable(=

) */

   pubic void processWrite (ByteBuffer writeBuffer, String host, in=

t

port) {
           // I cannot do dc.socket().write since the block=

ing is false.

           dc.send(writeBuffer, new InetSocketAddress (host=

, port));

   }
}

Is there a way to know the Sender after the receive call in the
Reader?


See above.

Kind regards

        robert

--
remember.guy do |as, often| as.you_can - without endhttp://blog.rubybestp=

ractices.com/

Hey Robert,
Thanks a ton for that. Really stupid on my part to not have checked
the return value of receive :D.

Thanks again
Bala

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