SDN Controller Programming Guide

Figure 16 OpenFlow Message Class Diagram

Each mutable subclass includes a private Mutable object that determines whether the instance is

still “writable”. While writable, the “payload” of the mutable message can be set. Once the

message has been made immutable, the immutable instance is marked as “no longer writable”;

any attempt to change its state will result in an InvalidMutableException being thrown.

Note that messages are passive in nature as they are simply data carriers.

Note also that structures (e.g. a Match) have a very similar class relationship.

Factories

Messages and structures are parsed or created by factories. Since the factories are all about

processing, but contain no state, the APIs consist entirely of static methods. Openflow messages

are created, encoded, or parsed by the MessageFactory class. Supporting structures are created,

encoded, or parsed by supporting factories, e.g. MatchFactory, FieldFactory, PortFactory, etc.

The main factory that application developers will deal with is the MessageFactory: