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copied!<p>Short answer: remove <code>OP_CONNECT</code> from the list of operations you are interested in for the accepted connection -- an accepted connection is already connected.</p> <p>I managed to reproduce the issue, which might be exactly what's happening to you:</p> <pre><code>import java.net.*; import java.nio.channels.*; public class MyNioServer { public static void main(String[] params) throws Exception { final ServerSocketChannel serverChannel = ServerSocketChannel.open(); serverChannel.configureBlocking(true); serverChannel.socket().bind(new InetSocketAddress("localhost", 12345)); System.out.println("Listening for incoming connections"); final SocketChannel clientChannel = serverChannel.accept(); System.out.println("Accepted connection: " + clientChannel); final Selector selector = Selector.open(); clientChannel.configureBlocking(false); final SelectionKey clientKey = clientChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_CONNECT); System.out.println("Selecting..."); System.out.println(selector.select()); System.out.println(selector.selectedKeys().size()); System.out.println(clientKey.readyOps()); } } </code></pre> <p>After the above server receives a connection, the very first <code>select()</code> on the connection exits without blocking and there are no keys with ready operations. I don't know why Java behaves in this way, but it appears many people get bitten by this behavior.</p> <p>The outcome is the same on Sun's JVM 1.5.0_06 on Windows XP as well as Sun's JVM 1.5.0_05 and 1.4.2_04 on Linux 2.6.</p>

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