How can you safely perform blocking operations in a Netty channel handler?
If an operation in Netty takes longer time to complete or is blocking it is advisable to perform that in a handler that uses a separate ExecutorGroup so that the main EventLoop thread is not blocked.
You can specify that during the pipeline creation.
Quoting an example that uses executor group for DB operation from ChannelPipeline javadoc
static final EventExecutorGroup group = new DefaultEventExecutorGroup(16); ... ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast("decoder", new MyProtocolDecoder()); pipeline.addLast("encoder", new MyProtocolEncoder()); // Tell the pipeline to run MyBusinessLogicHandler's event handler methods // in a different thread than an I/O thread so that the I/O thread is not blocked by // a time-consuming task. // If your business logic is fully asynchronous or finished very quickly, you don't // need to specify a group. pipeline.addLast(group, "handler", new MyBusinessLogicHandler());