java.nio.channels.ClosedChannelException

Question

How can i solve this problem. I got following error:

java.nio.channels.ClosedChannelException

This is coding:

 public void run() {

    try {
        SocketChannel socketChannel = (SocketChannel) key.channel();
        ByteBuffer buffer = ByteBuffer.allocate(512);
        int i1 = socketChannel.read(buffer);

        if (buffer.limit() == 0 || i1 == -1) {

            Socket s = null;
            try {
                s = socketChannel.socket();
                s.close();
                key.cancel();
            } catch (IOException ie) {
                if (UnitDataServer.isLog) {
                    log.error("Error closing socket " + s + ": " + ie);
                }
            }
        } else {
            buffer.flip();
            if (UnitDataServer.isLog) {
                log.info(" Recvd Message from Unit : " + buffer.array());
            }
            byte byteArray[] = buffer.array();
            log.info("Byte Array length :" + byteArray.length);
            hexString = new StringBuffer();

            for (int i = 0; i < i1 /* byteArray.length */; i++) {
                String hex = Integer.toHexString(0xFF & byteArray[i]);
                if (hex.length() == 1) {
                    // could use a for loop, but we're only dealing with a
                    // single byte
                    hexString.append('0');
                }
                hexString.append(hex);
            }
            hexString.trimToSize();
            log.info("Hex String :" + hexString);

             Communicator.dataReceive(new  DataReceive(
                    socketChannel, hexString.toString(), dst));

        }
    } catch (Exception e) {
        if (UnitDataServer.isLog) {
            // log.error(e);
        }
        try {
            socketChannel.socket().close();
            key.cancel();
        } catch (IOException ex) {
            if (UnitDataServer.isLog) {
                log.error(ex);
            }
        }
    }
}

Answer 1

You have closed the channel and are still trying to use it.

There are several issues with your code.

First, your test for EOS is faulty. Remove the limit() == 0 test. That doesn't indicate EOS, it just indicates a zero length read, which can happen in non-blocking mode at any time. It doesn't mean the peer has closed his end of the connection, and it doesn't mean you should close your end.

Second, closing a channel closes the socket as well. You should close the channel only, not the socket.

Third, closing a channel cancels the key. You don't need to follow every close with a cancel.

You may also have failed to check whether a ready key is valid in the select loop before using it, e.g. for reading.

I continue to be amazed, and amused, and bemused, by the claim elsewhere in this thread that 'source code is untrue' under some circumstances.

Answer 2

You need to fix/secure code that is throwing this exception. ClosedChannelException is ...

... thrown when an attempt is made to invoke or complete an I/O operation upon channel that is closed, or at least closed to that operation. That this exception is thrown does not necessarily imply that the channel is completely closed. A socket channel whose write half has been shut down, for example, may still be open for reading

(as described in Java 6 API)

But really, you would need to provide us code snipped and stack trace in order to get more detailed help.