Importing a OSGi service that is a singleton bean (that has a factory method)

Question

How do I import the exported OSGi service that's a Singleton bean?

I end up getting the Exception as follows:

Unable to start blueprint container for bundle opaClient
org.osgi.service.blueprint.container.ComponentDefinitionException: Unable to find a matching constructor on class com.opa.gateway.OPAGateway for arguments [] when instantiating bean opaGateway
    at org.apache.aries.blueprint.container.BeanRecipe.getInstance(BeanRecipe.java:336)

---

My Blueprint xml where the service is exported is as follows:

<bean id="opaGateway" class="com.opa.gateway.OPAGateway" factory-method="getInstance"/>
<service ref="opaGateway" interface="com.opa.gateway.IOPAGateway" />

And the service is referenced in another bundle as follows:

<reference interface="com.opa.gateway.OPAGateway" component-name="opaGateway" availability="mandatory" />

Is there a way to directly reference a singleton bean that's a OSGi service?

Answer 1

Yes, you can reference a singleton which is an OSGi service. Make sure (as @Balazs suggested) that your class has a static function/method getInstance() with no arguments.

Have a look at the blueprint below. Hope it gives you a clue... (If you need the complete sample I can try to post it.

<bean   id="opaGateway"
        class="org.test.OPAGateway" factory-method="getInstance">
</bean>

<bean id="opaClient"
      class="org.test.client.OPAClient"
        init-method="startup"
        destroy-method="shutdown">
</bean>

<service ref="opaGateway" interface="org.test.IOPAGateway" />


<reference interface="org.test.IOPAGateway" availability="optional">
    <reference-listener bind-method="setOPAGateway"
                    unbind-method="unsetOPAGateway">
        <ref component-id="opaClient"/>
    </reference-listener>
</reference>

• bean opaGateway (org.test.OPAGateway). It is a class implementing org.test.IOPAGateway. It is instantiated by static method getInstance():

  public class OPAGateway implements IOPAGateway {
      private static OPAGateway instance = null;
  
      public static OPAGateway getInstance () {
          if(instance == null) {
              instance = new OPAGateway();
          }
          return instance;
      }
  
      // A very simple method...
      @Override
      public String printMessage() {
          return "I AM AN OPAGATEWAY";
      }
  }
  

• bean: opaClient: It is just a consumer or the class that references the opaGateway:

  public class OPAClient {
      public void setOPAGateway(IOPAGateway c) {
          if(c != null) {
              System.out.println("Message: " + c.printMessage());
          }
      }
      public void unsetOPAGateway(IOPAGateway c) {
  
      }
  }
  

• The reference-listener: Injects the instance of opaGateway in the opaClient using the bind/unbind-method.

You can find more information here: http://www.ibm.com/developerworks/library/os-osgiblueprint/