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Netty-in-Action-Chapter 1

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Chapter 1 - Netty - asynchronous and event-driven

Networking in Java

Previously we have to use one thread per connection to do the read/write, this has problems:

  1. Resource waste
  2. Memory allocation
  3. Limit on number of threads supported by JVM

Java blocking I/O

Selector

It's the key for JAVA NIO, it uses event notification API to indicate if a socket is done read/write

Introducing Netty

Netty feature summary

Netty's core components

Channel

Just like a car with incoming and outcoming messages

Callbacks

Netty uses callbacks internally when handling events; when a callback is triggered the event can be handled by an implementation of interface ChannelHandler. The next listing shows an example: when a new connection has been established the ChannelHandler callback channelActive() will be called and will print a message.
Netty callback

Future

  1. Provide a way to notify the application when the operation is completed
  2. Java's Future can only provide manual check for the status of the operation
  3. Netty's Future does not need to do manual check anymore
  4. Netty's ChannelFuture is able to let you register to the ChannelFutureListener interfaces, the listener has a callback has a callback methods for indication of completion

Netty Future 1
Netty Future 2

Events and handlers

Summary

Future, Callbacks and Handlers: provide a processing environment that allows the logic of your application to evolve independently of any concerns with network operations.
Selectors, Events, and EventLoops: abstracts the Selector away from the application by firing events, eliminating all the handwritten dispatch code that would otherwise be required, also eliminates any concern you might have about synchronization in ChannelHandlers.