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Asked: 2026-06-05T01:08:44+00:00

I want to write raw bytes to a netty Channel. I thought I could

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I want to write raw bytes to a netty Channel. I thought I could do this by first creating a ChannelBuffer, filling it with bytes (coming from, say, a Kryo serializer), and then writing that ChannelBuffer to the netty Channel.

Here is the relevant code, where I’m simply filling some bytes into a ChannelBuffer in the ctor and trying to send it upon connection:

/**
 * Handler implementation for the object echo client.  It initiates the
 * ping-pong traffic between the object echo client and server by sending the
 * first message to the server.
 */
public class ObjectEchoClientHandler extends SimpleChannelUpstreamHandler {

private final ChannelBuffer firstMessage;

/**
 * Creates a client-side handler.
 */
public ObjectEchoClientHandler(int firstMessageSize) {
    if (firstMessageSize <= 0) {
        throw new IllegalArgumentException(
                "firstMessageSize: " + firstMessageSize);
    }
    firstMessage = ChannelBuffers.buffer(8192);
    for (int i = 0; i < firstMessageSize; i++) {
        firstMessage.writeByte(i % 256);
    }
}

@Override
public void channelConnected(
        ChannelHandlerContext ctx, ChannelStateEvent e) {

    // Send the first message if this handler is a client-side handler.
    // e.getChannel().write(firstMessage);
    Channels.write(ctx, e.getFuture(), firstMessage);
}

}

This doesn’t seem to work, as it throws this exception:

java.io.NotSerializableException: org.jboss.netty.buffer.BigEndianHeapChannelBuffer
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
at org.jboss.netty.handler.codec.serialization.ObjectEncoder.encode(ObjectEncoder.java:80)
at org.jboss.netty.handler.codec.oneone.OneToOneEncoder.handleDownstream(OneToOneEncoder.java:61)
at org.jboss.netty.channel.Channels.write(Channels.java:626)
at org.jboss.netty.channel.Channels.write(Channels.java:587)
at ca.gsimard.spacecraft.client.ObjectEchoClientHandler.channelConnected(ObjectEchoClientHandler.java:83)
at ca.gsimard.spacecraft.client.ObjectEchoClientHandler.handleUpstream(ObjectEchoClientHandler.java:75)
at org.jboss.netty.channel.Channels.fireChannelConnected(Channels.java:227)
at org.jboss.netty.channel.socket.nio.NioWorker$RegisterTask.run(NioWorker.java:784)
at org.jboss.netty.channel.socket.nio.NioWorker.processRegisterTaskQueue(NioWorker.java:250)
at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:192)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)

I’m sure this is dead trivial and probably the wrong way of doing it, because I can’t seem to find anyone who had the same error as this. I’m using Netty 3.3.0 right now.

I can get this to work by creating a properly sized byte[] and copying the contents of the ChannelBuffer to it, but I would have liked a more direct solution that avoids useless byte copying.

    byte[] array = new byte[firstMessage.writerIndex()];
    firstMessage.readBytes(array);
    e.getChannel().write(array);

Thanks for any pointers !

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1 Answer

  1. Editorial Team

    Looking at your stack trace, I observed these two lines:

    at org.jboss.netty.handler.codec.serialization.ObjectEncoder.encode(ObjectEncoder.java:80)
at org.jboss.netty.handler.codec.oneone.OneToOneEncoder.handleDownstream(OneToOneEncoder.java:61

    What this means to me is that your pipeline contains an ObjectEncoder which is attempting to serialize a ChannelBuffer. Since your objects have already been encoded by Kryo, you don’t need the ObjectEncoder.

    Or put differently (without Kryo), a ChannelBuffer should be the output of the ObjectEncoder and your object should be the input.

    Your best bet is to write a new ChannelHandler that uses Kryo to encode your objects. You may find some added efficiencies when Kryo does it’s job as a handler in the Netty pipeline.

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