Design patterns plays important role in the Software
Development. It will define the reusable implementation to the commonly occurred
problems. Usually in software development, we can see same problem repeatedly coming
in the applications. To address these common problems, expert people came up
with solution called design patterns. Design patterns define the solution so
that we can implement solution to address the the common problems.
Follow Liferay DXP/7 Tutorial to get more information.
Whiteboard
Design pattern is commonly and wide used pattern in OSGi implementations.
OSGi Service Registry implemented on
White Board Design Patter.
Liferay 7 / DXP have used OSGi Declarative Services
(DS) to implements Liferay application modules. It is good to know White Board
design pattern and Service Registry. It will give more idea about component services
and its working.
When we work with Declarative
Service Framework, bundle have several components and these components
depends on other components.
Usually component have services and these services
shared among other components. Service Registry
manage the services registration information and its dependency service
information. It will manage services and its references information.
To manage these things OSGi have Service Registry that is based on Whiteboard Design Pattern.
White Board Design pattern will provide the mechanism
to register the different component services and the dependency component can easily
find it reference service based on their needs. Whenever new service implementation
register with Service Registry then dependency will get to know the information
so that it can find appropriate dependency service.
Assume Component C1
have service S1 and perform certain
task, it needed other service it means service S1 depends on other component services.
Assume S1
service can have several option that can perform task, it means several component
provides their services to S1 and S1 can choose any of that service to full
fill the requirement. Now S1 have
options like C2 component Service S2 and C3
Components Service S3.
To provide these dependency service information or
reference service information we need other component so that S1 service can identify
its dependent service. To provide this king information we need other component
called Whiteboard or Service Registry.
When the component is activated, all the services are
register with Whiteboard / Service Registry.
Now C1 component Service S1 can identify, it’s
required dependent service from the Whitboard / Service Registry to complete or
perform the task.
Here S1
have several option, it can choose any of the service based on its requirement.
S1 will use some additional properties to identify the required service at the
point of the time. Such a way whiteboard
design pattern have used in OSGi to implement Service Registry.
Service Registry is key component in the OSGi
implementation and OSGi Declarative Service have used Service Registry to
provide dependency mechanism among the component services. OSGi
Declarative Service is core framework to develop OSGi components and its
services.
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