Java Reference
In-Depth Information
19.4.2
Design
Control module architecture is inspired by the EJB model, which introduces
the distinction between component (the Java Bean) and container (the
component server). We have already adopted this solution in Prototype 3 of
Chapter 15 where we had to manage the concurrent access of remote clients
to the GIS databases.
Decision point
How does the control module manage the execution of multiple concurrent
tasks?
The framework offers two abstract classes to support multiple concurrent
tasks:
DActivity
and
DProcess
. A
DActivity
object represents an independent
sequential thread of execution belonging to a unique
DProcess
owner,
embeds the dynamic specification of its task, and has internal data.
The
DActivity
class has to be redefined for every concrete specification
that implements the logic of a control service.
DProcess
is the base class of
every control module. It encapsulates a collection of
DActivity
objects and
has to be redefined in order to encapsulate specific resources. Figure 19.2
shows the class diagram that depicts the architecture of the control module.
The right-hand side of the figure indicates the framework classes, while the
left-hand side indicates their customization for a given application.
ControlModule
DProcess
Runnable
void startService()
void stopService()
void startActivity()
void stopActivity()
Service
DActivity
void init()
void step()
void quit()
public void run()
void start()
void stop()
protected void init()
protected void step()
protected void quit()
Figure 19.2
The basic architecture of a control module
