reference from：http://www.cs.bgu.ac.il/~spl051/Personal_material/Practical_sessions/Ps_12/ps12.html

• Java server class with multiple client connections: one-to-one ratio of threads to clients, therefore enormous thread overhead, resulted in performance problems and lack of scalability. The main problem is blocking I/O calls.
• JDK 1.4 supports non-blocking I/O calls (java.nio and java.nio.channels). These packages were designed principally according to Reactor design pattern (Using Design Patterns to Develop Reusable Object-Oriented Communication Software by Douglas C. Schmidt).

The actors in Reactor pattern are:

? Handles, which identify resources (such as network connections, open files, and synchronization

objects) that are managed by an operating system.

? Reactor, which defines an interface for registering, removing, and dispatching Event Handler

objects. An implementation of the Reactor interface provides a set of application-independent

event demultiplexing and dispatching mechanisms. These mechanisms dispatch application-specific

Event Handler in response to events occurring on one or more Handles.

? Event Handler, which specifies an interface used by the Reactor to dispatch callback methods

defined by objects that are pre-registered to handle certain types of events (such as input events,

output events, and signals).

? Concrete Event Handler, which implements the customized callback method(s) that process events

in an application-specific manner.

Using Reactor in Communication Software

• Short tutorial
• Important classes in java.nio.channels:
• SocketChannel, ServerSocketChannel
•  Selector (Reactor)
•  SelectionKey
• java.nio: ByteBuffer

Example

• Reactor
• ConnectionAcceptor (Event Handle)
• ConnectionReader (Event Handle)
• MessageProcessorTask
• SimpleClient
• ThreadPool