Netty How to send an object

Question

How to send an object using netty. When i try to send a String object everything is ok.

channel.writeAndFlush(new String("df"));

But when i try to send an simple object server get errors

public class Message implements Serializable {

    private static final long serialVersionUID = 1L;
}
channel.writeAndFlush(new Message()); 

---

io.netty.channel.DefaultChannelPipeline$TailHandler exceptionCaught
WARNING: An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
io.netty.handler.codec.DecoderException: java.lang.NullPointerException
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:259)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:141)
    at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:340)
    at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:326)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:116)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:494)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:461)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:378)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:350)
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101)
    at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.NullPointerException
    at io.netty.handler.codec.serialization.CompactObjectInputStream.readClassDescriptor(CompactObjectInputStream.java:55)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1601)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at io.netty.handler.codec.serialization.ObjectDecoder.decode(ObjectDecoder.java:73)
    at io.netty.handler.codec.LengthFieldBasedFrameDecoder.decode(LengthFieldBasedFrameDecoder.java:343)
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:228)
    ... 11 more

---

class ChatServerInitializer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel arg0) throws Exception
    {
        ChannelPipeline pipeline = arg0.pipeline();
        pipeline.addLast("decoder", (new ObjectDecoder(null)));  
        pipeline.addLast("encoder", new ObjectEncoder());  
        pipeline.addLast("handler", new ChatServerHandler());
    }
}

Answer 1

You specified null when you construct a ObjectDecoder and that's causing a NullPointerException here. Instead, you have to specify something like ClassResolvers.weakCachingResolver(MyMessage.class.getClassLoader()).

Answer 2

it is not right:

new ObjectDecoder(null)

Try to do like this:

    serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
        @Override
        protected void initChannel(SocketChannel socketChannel) throws Exception {
            socketChannel.pipeline().addLast(
                    new ObjectDecoder(ClassResolvers.softCachingResolver(ClassLoader.getSystemClassLoader())),
                    new ObjectEncoder(),
                    new Handler());
        }
    });