Steps for Building Declarative Services

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1. Study the Interfaces

• Bundle
• BundleContext
• BundleActivator

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2. Define the Bundle Service Interface

package cs.ecl.osgi.simple.declarativeservice.say;

public interface Sayable {
	String say();
}

An implementation of this interface could be:

package cs.ecl.osgi.simple.declarativeservice.say.internals;
import java.util.Date;
import cs.ecl.osgi.simple.declarativeservice.say.Sayable;

public class TodaySay implements Sayable {
	public String say() {
		return " Declarative Service: Today is " + new Date();
	}
}

The relationships between the interface that is exposed to the client and the implementation that is hidden, must be defined in a xml file:

<?xml version="1.0"?>
<component name="sayable">
	<implementation class="cs.ecl.osgi.simple.declarativeservice.say.internals.TodaySay"/>
	<service>
		<provide interface="cs.ecl.osgi.simple.declarativeservice.say.Sayable"/>
	</service>
</component>

The bundle consumer must implement the CommandProvider interface

package cs.ecl.osgi.simple.declarativeservice.consumer;

import org.eclipse.osgi.framework.console.CommandInterpreter;
import org.eclipse.osgi.framework.console.CommandProvider;

import cs.ecl.osgi.simple.declarativeservice.say.Sayable;

public class SaySingleConsumer implements CommandProvider {

	private Sayable s;

	public synchronized void bindSayable(Sayable s) {
		this.s = s;
	}

	public synchronized void unbindSayable(Sayable s) {
		this.s = null;
	}

	public synchronized void _run(CommandInterpreter ci) {
		if (s != null) {
			System.out.println(s.say());
		} else {
			ci.println("Error, No Service of type Sayable available");
		}
	}

	@Override
	public String getHelp() {
		return "\n\t run - EXECUTE the Sayable service";
	}
}