As far as I understand, in Netty ChannelOutboundHandlerAdapter is meant for outbound IO operations: that is writes, but a class implementing ChannelOutboundHandlerAdapter can also implement a read method, which seems incorrect to me, why should a component meant for writing have a read method.
The opposite component, that is ChannelInboundHandlerAdapter which is meant for inbound IO operations, ie reads, does not have a write method. This sounds correct.
Why does ChannelOutboundHandlerAdapter makes it possible to implement a read method if it is supposed to push data out of the pipeline?
read() signals the willingness to read something from the socket as soon as there is something that can be read. It basically tells netty that we should do a read at some point.