// The connection is closed when a write operation cannot finish in 30 seconds.

public class MyChannelInitializer extends ChannelInitializer<Channel> {
    public void initChannel(Channel channel) {
        channel.pipeline().addLast("writeTimeoutHandler", new WriteTimeoutHandler(30);
        channel.pipeline().addLast("myHandler", new MyHandler());
    }
}

// Handler should handle the WriteTimeoutException.
public class MyHandler extends ChannelDuplexHandler {
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
            throws Exception {
        if (cause instanceof WriteTimeoutException) {
            // do something
        } else {
            super.exceptionCaught(ctx, cause);
        }
    }
}

ServerBootstrap bootstrap = ...;
...
bootstrap.childHandler(new MyChannelInitializer());
...