Blueprint is a dependency injection framework for OSGi that simplifies service management by providing automatic dependency resolution and lifecycle management. It is an alternative to Declarative Services (DS) and is inspired by the Spring Framework, making it easier to manage complex OSGi applications.
* Dependency Injection – Injects services and configuration into components automatically.
* Automatic Service Tracking – Dynamically handles service availability and unavailability.
* Asynchronous Service Dependency Handling – Waits for required services before activating components.
* XML-Based Configuration – Uses XML instead of Java annotations or code.
* Extensible – Can integrate with other frameworks like Spring.
Blueprint provides a central XML configuration file where components (beans) and services are defined. The Blueprint container manages component lifecycle, dependencies, and service registrations automatically.
A service interface in Java:
public interface MyService {
void sayHello();
}
A service implementation:
public class MyServiceImpl implements MyService {
public void sayHello() {
System.out.println("Hello from Blueprint OSGi Service!");
}
}
OSGI-INF/blueprint.xml)<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
<!-- Define the Service Implementation Bean -->
<bean id="myServiceBean" class="com.example.MyServiceImpl" />
<!-- Register the Service -->
<service id="myService" interface="com.example.MyService">
<bean ref="myServiceBean" />
</service>
</blueprint>
* This creates and registers MyServiceImpl as an OSGi service.
A consumer component that depends on the MyService:
public class MyConsumer {
private MyService myService;
public void setMyService(MyService myService) {
this.myService = myService;
}
public void start() {
myService.sayHello();
}
}
Modify blueprint.xml to inject the service:
<bean id="myConsumer" class="com.example.MyConsumer">
<property name="myService" ref="myService" />
</bean>
* The Blueprint container automatically injects MyService into MyConsumer.
| Feature | Blueprint | Declarative Services (DS) |
|---|---|---|
| Configuration | XML-based | Java annotations (@Component, @Reference) |
| Dependency Injection | Yes (Spring-like) | Yes |
| Service Handling | Automatic with XML | Automatic with Java |
| Lifecycle Management | Managed via XML | Managed via annotations |
| Complexity | Good for large projects | Easier for small projects |
| Asynchronous Handling | Yes | Yes |
* Easy Dependency Injection – Reduces boilerplate code.
* Loose Coupling – Decouples service consumers and providers.
* Automatic Lifecycle Management – Handles dynamic service availability.
* Spring-Like Development – Familiar to developers with Spring experience.