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To register a service, your can annotate your class with a @Service @Component annotation, and an instance of your class will be registered under all directly implemented interfaces into the OSGi registry. You can however take control on the interfaces to be exposed, and in this case, you can use the provides attribute, which takes a list of classes to expose from the registry.

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Now we have introduced the background, here is the SpellCheck component:

Code Block

@Service@Component(provides={SpellChecker.class},
           properties={@Property(name=CommandProcessor.COMMAND_SCOPE, value="dmsample.annotation"),
                       @Property(name=CommandProcessor.COMMAND_FUNCTION, values={"spellcheck"})})
public class SpellChecker {
    // --- Gogo Shell command

    @Descriptor("checks if word is found from an available dictionary")
    public void spellcheck(@Descriptor("the word to check")String word) {
       // Check the proper existence of the word parameter, using injected DictionaryService instances
       // ...
    }
}

In the code above, you see that the SpellCheck is annotated with the @Service @Component annotation. Gogo runtime does not required shell commands to implement a specific interface. Commands just have to register some Pojos in the OSGi registry, but the only thing required is to provide the Pojos with two service properties ( COMMAND_SCOPE, and COMMAND_FUNCTION) which will be used by the Gogo runtime when instropecting the Pojo for invoking the proper functions.

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And here is our previous SpellChecker component, augmented with two new ServiceDependency annotations:

Code Block

@Service@Component(provides={SpellChecker.class},
                   properties={@Property(name=CommandProcessor.COMMAND_SCOPE, value="dmsample.annotation"),
                                           @Property(name=CommandProcessor.COMMAND_FUNCTION, values={"spellcheck"})})
public class SpellChecker {
    @ServiceDependency(required = false)
    private LogService m_log;

    private CopyOnWriteArrayList<DictionaryService> m_dictionaries = new CopyOnWriteArrayList<DictionaryService>();

    @ServiceDependency(removed = "removeDictionary")
    protected void addDictionary(DictionaryService dictionary) {
        m_dictionaries.add(dictionary);
    }
    
    protected void removeDictionary(DictionaryService dictionary) {
        m_dictionaries.remove(dictionary);
    }

    // --- Gogo Shell command

    @Descriptor("checks if word is found from an available dictionary")
    public void spellcheck(@Descriptor("the word to check")String word)
    {
        m_log.log(LogService.LOG_INFO, "Checking spelling of word \"" + word
            + "\" using the following dictionaries: " + m_dictionaries);

        for (DictionaryService dictionary : m_dictionaries)
        {
            if (dictionary.checkWord(word))
            {
                System.out.println("word " + word + " is correct");
                return;
            }
        }
        System.err.println("word " + word + " is incorrect");
    }
}

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Creating a Service from ConfigAdmin

The @Service @Component annotation is not the only one for creating services. Another one is the @FactoryConfigurationAdapterService annotation which allows to instantiate many instances of the same annotated service class from ConfigAdmin (and WebConsole). To illustrate this, let's take a look at our DictionaryImpl class which is part of the SpellChecker sample. This service is required by the SpellChecker component, when checking for proper word existence. And you can instantiate as many DictionaryService as you want, from ConfigAdmin ...

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Creating a Service from ConfigAdmin