Re: Retrieving Sender Information From A Non-blocking DatagramChannel

From:
Robert Klemme <shortcutter@googlemail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 24 Oct 2011 22:41:28 +0200
Message-ID:
<9gm0s4FjsaU1@mid.individual.net>
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 within
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/DatagramChannel.html#receive(java.nio.ByteBuffer)

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, int
port) {
        // I cannot do dc.socket().write since the blocking 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 end
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