Greedy Policy Option Application

The Greedy Policy Option sample provides two portlets that can be added to a Liferay DXP page: Greedy Portlet and Reluctant Portlet.

Figure 1: The Greedy Policy Option app provides two portlets that only print text. You'll dive deeper later to discover their interesting capabilities involving services.

These two portlets do not provide anything useful out-of-the-box. They are, however, very effective at demonstrating the ability to reference services using greedy and reluctant policy options. You’ll learn how to do this later.

What API(s) and/or code components does this sample highlight?

This sample provides two modules referencing services using greedy and reluctant policy options.

• service-reference: Provides an OSGi service interface called SomeService, a default implementation of it, and portlets that refer to service instances. One portlet refers to new higher ranked instances of the service automatically. The other portlet is reluctant to use new higher ranked instances and continues to use its bound service. The reluctant portlet can, however, be configured dynamically to use other service instances.

• higher-ranked-service: Has a higher ranked SomeService implementation.

Here are each module’s file structures:

• service-reference/

  • bnd.bnd
  • configs/
    • com.liferay.blade.reluctant.vs.greedy.portlet.portlet.ReluctantPortlet.config → ReluctantPortlet configuration file
  • src/main/java/com/liferay/blade/reluctant/vs/greedy/portlet/
    • api/
      • SomeService.java → Service interface
    • constants/
      • ReluctantPortletVsGreedyPortletKeys.java → Portlet constants
    • portlet/
      • DefaultSomeService.java → Zero ranked service implementation
      • GreedyPortlet.java → Refers to SomeService using a greedy service policy option
      • ReluctantPortletPortlet.java → Refers to SomeService using a reluctant service policy option by default.

• higher-ranked-service/

  • bnd.bnd
  • src/main/java/com/liferay/blade/reluctant/vs/greedy/svc/HigherRankedService.java → Service implementation with service ranking value of 100

How does this sample leverage the API(s) and/or code component?

Here are the things you can learn using the sample modules:

1. Binding a component’s service reference to the highest ranked service instance that’s available initially.

2. Deploying a module with a higher ranked service instance for binding to greedy references immediately.

3. Configuring a component to reference a different service instance dynamically.

Let’s walk through the demonstration.

Binding a newly deployed component’s service reference to the highest ranking service instance that’s available initially

On deploying a component that references a service, it binds to the highest ranking service instance that matches its target filter (if specified).

The portlet classes refer to instances of interface SomeService. The doSomething method returns a String.

public interface SomeService {

    public String doSomething();

}

Class DefaultSomeService implements SomeService. Its doSomething method returns the String “I am Default!”.

@Component
public class DefaultSomeService implements SomeService {

    @Override
    public String doSomething() {
        return "I am Default!";
    }

}

When module’s portlets refer to DefaultSomeService, they display the String “I am Default!”.

The ReluctantPortlet class’s SomeService reference’s policy option is the default: static and reluctant. This policy option keeps the reference bound to its current service instance unless that instance stops or the reference is reconfigured to refer to a different service instance.

@Component(
   immediate = true,
   property = {
       "com.liferay.portlet.display-category=category.sample",
       "com.liferay.portlet.instanceable=true",
       "javax.portlet.display-name=Reluctant Portlet",
       "javax.portlet.init-param.template-path=/",
       "javax.portlet.init-param.view-template=/view.jsp",
       "javax.portlet.name=" + ReluctantVsGreedyPortletKeys.Reluctant,
       "javax.portlet.resource-bundle=content.Language",
       "javax.portlet.security-role-ref=power-user,user"
    },
    service = Portlet.class
  )
public class ReluctantPortlet extends MVCPortlet {

   @Override
   public void doView(
           RenderRequest renderRequest, RenderResponse renderResponse)
       throws IOException, PortletException {

       renderRequest.setAttribute("doSomething", _someService.doSomething());

       super.doView(renderRequest, renderResponse);
   }

    @Reference
    private SomeService _someService;

}

The ReluctantPortlet’s method doView sets render request attribute doSomething to the value returned from the SomeService instance’s doSomething method (e.g., DefaultService returns “I am default!”).

The GreedyPortlet class is similar to ReluctantPortlet, except its SomeService reference’s policy option is static and greedy (i.e., ReferencePolicyOption.GREEDY).

public class GreedyPortlet extends MVCPortlet {

  @Override
	public void doView(
  		RenderRequest renderRequest, RenderResponse renderResponse)
  	throws IOException, PortletException {

  	renderRequest.setAttribute("doSomething", _someService.doSomething());

  	super.doView(renderRequest, renderResponse);
	}

	@Reference (policyOption = ReferencePolicyOption.GREEDY)
	private SomeService _someService;

}

The greedy policy option lets the component switch to using a higher ranked SomeService instance if one becomes active in the system. The section Deploying a module with a higher ranked service instance for binding to greedy references immediately demonstrates this portlet switching to a higher ranked service.

It’s time to see this module’s portlets and service in action.

1. Stop module higher-ranked-service if it’s active.

2. Deploy the service-reference module.

3. Add the Reluctant Portlet from the Add → Widgets → Sample category to a site page.

   The portlet displays the message “SomeService says I am Default!”–whose latter part comes from the render request attribute set by the DefaultService instance.

   

   Figure 2: *Reluctant Portlet* displays the message "SomeService says I am Default!"

4. Add the Greedy Portlet from the Add → Widgets → Sample category to a site page.

   The portlet displays the message “SomeService says I am better, use me!”. Both portlets are referencing a DefaultService instance.

   

   Figure 3: *Greedy Portlet* displays the message "SomeService says I am better, use me!"

Since DefaultService is the only active SomeService instance in the system, the portlets refer to it for their SomeService fields.

The DefaultService and portlets Reluctant Portlet and Greedy Portlet are active. Let’s activate a higher ranked SomeService instance and see how the portlets react to it.

Deploying a module with a higher ranked service instance for binding to greedy references immediately

Module higher-ranked-service provides a SomeService implementation called HigherRankedService. HigherRankedService’s service ranking is 100–that’s 100 more than DefaultService’s ranking 0. Its doSomething method returns the String “I am better, use me!”.

1. Deploy the higher-ranked-service module.
2. Refresh your page that has the portlets Reluctant Portlet and Greedy Portlet.

Reluctant Portlet continues displaying message “SomeService says I am better, use me!”. It’s “reluctant” to unbind from the DefaultService instance and bind to the newly activated HigherRankedService service.

Greedy Portlet displays a new message “SomeService says I am better, use me!”. The part of the message “I am better, use me!” comes from the HigherRankedService instance to which it refers.

Figure 4: The *Greedy Portlet* is using a `HigherRankedService` instance

Next, learn how to bind the Reluctant Portlet to a HigherRankedService instance.

Configuring a component to reference a different service instance dynamically

The Reluctant Portlet is currently bound to a DefaultService instance. It’s “reluctant” to unbind from it and bind to a different service. OSGi Configuration Administration lets you reconfigure service references to filter on and bind to different service instances.

The service-reference module’s configuration files and com.liferay.blade.reluctant.vs.greedy.portlet.portlet.ReluctantPortlet.config and com.liferay.blade.reluctant.vs.greedy.portlet.portlet.ReluctantPortlet.cfg configure the ReluctantPortlet component to use a HigherRankedService instance.

_someService.target=(component.name=com.liferay.blade.reluctant.vs.greedy.service.HigherRankedService)

The service configuration filters on a service whose component.name is com.liferay.blade.reluctant.vs.greedy.service.HigherRankedService.

Note: For deploying to Liferay DXP 7.2, use file with suffix .config. For earlier versions (i.e., Liferay DXP 7.0 Fix Packs earlier than Fix Pack 8 and Liferay CE Portal 7.0 GA3 or earlier), use the file with suffix .cfg.

Here are the steps to reconfigure ReluctantPortlet to use HigherRankedService:

1. Copy the configuration file to [Liferay-Home]/osgi/configs.
2. Refresh your browser.

Reluctant Portlet displays a new message “SomeService says I am better, use me!”.

Figure 5: *Reluctant Portlet* is using the `HigherRankedService` instance instead of a `DefaultService` instance.

Reluctant Portlet is using HigherRankedService instance instead of a DefaultService instance. You’ve configured Reluctant Portlet to use a HigherRankedService instance!

Where Is This Sample?

There are three different versions of this sample, each built with a different build tool:

• Gradle
• Liferay Workspace
• Maven