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Gravia is the Fuse Portable Runtime. Traditionally tied to OSGi, Gravia is designed to make the Fuse Integration Platform available on a set of supported target containers.
The set of supported target containers includes but is not limited to
- Provide a Dynamic Services API as the basis of component integration
- Provide Declarative Services and Configuration Admin functionality
- Provide a modularity layer that works with the modularity concepts provided by the target container
- Provide an abstraction for Resources with associated Capabilities and Requirements
- Provide an Resolver that can find a consistent solution given a set of Capabilities and Requirements
- Provide a Repository of actual Resource artefacts as well as abstract Feature Resources
- Provide a Provisioner that can provision the Runtime using the Repository and Resolver
- Provide a deployment model that works across all supported target containers
The Gravia Runtime comes in two flavours
- Embedded Runtime
- OSGi Runtime
The Embedded Runtime is used with target containers that do not natively support OSGi (e.g. Tomcat, Wildfly). The OSGi Runtime is used on OSGi containers (e.g. Apache Felix, Equinox)
The Gravia Runtime supports a Modules and Services API that should look familiar to those who know OSGi. It is however no replacement of an OSGi Framework, instead it provides a subset of OSGi functionality in its own portable API.
Using the Gravia API allows projects to take advantage of the successful Dynamic Services API from OSGi including Declarative Services and Configuration Admin without the OSGi modularity layer.
Configurable components that use Declarative Services annotations will work in any target environment including Tomcat, WildFly or a plain JUnit test.
Internally, Gravia uses the unmodified implementations of Felix SCR, Config Admin, Metatype and Log Service. The internal dependency on the OSGi API is bridged to the Gravia Modules and Services API.
Application code would use the Gravia Runtime API only and hence be portable across various target environments.
When running in an OSGi environment, Gravia provides a simple bridging API that maps Gravia Modules to OSGi Bundles and Gravia Services to OSGi Services. It is therefore possible to gradually migrate application code away from OSGi, but keep running in an OSGi Framework. When migration is complete, the application would automatically work in non-OSGi environments too. Gravia maintains the API semantics across target environments.