Figure 9 shows an overview of the OSGi transaction architecture in Fuse ESB Enterprise. The core of the architecture is a JTA transaction manager based on Apache Geronimo, which exposes various transaction interfaces as OSGi services.

Figure 9. OSGi Transaction Architecture

The JTA Transaction Services Specification section of the OSGi Service Platform Enterprise Specification describes the kind of transaction support that can (optionally) be provided by an OSGi container. Essentially, OSGi mandates that the transaction service is accessed through the Java Transaction API (JTA).

The transaction service exports the following JTA interfaces as OSGi services (the JTA services):

Only one JTA provider should be made available in an OSGi container. In other words, the JTA services are registered only once and the objects obtained by importing references to the JTA services must be unique.

The Fuse ESB Enterprise transaction service exports the following Spring interface as an OSGi service:

By obtaining a reference to the PlatformTransactionManager OSGi service, it is possible to integrate application bundles written using the Spring transaction API into the Fuse ESB Enterprise transaction architecture.

Fuse ESB Enterprise provides an OSGi-compliant implementation of the transaction service through the Apache Aries transaction feature, which consists mainly of the following bundles:

org.apache.aries.transaction.manager
org.apache.aries.transaction.wrappers
org.apache.aries.transaction.blueprint

The Aries transaction feature exports a variety of transaction interfaces as OSGi services (making them available to other bundles in the container), as follows:

The PlatformTransactionManager OSGi service and the JTA services access the same underlying transaction manager.

To access the Fuse ESB Enterprise transaction implementation, you must install the transaction feature. In a standalone container, enter the following console command:

karaf@root> features:install transaction

If you are deploying into a fabric, add the transaction feature to your application's profile.

The underlying implementation of the Fuse ESB Enterprise transaction service is provided by the Apache Geronimo transaction manager. Apache Geronimo is a full implementation of a J2EE server and, as part of the J2EE implementation, Geronimo has developed a sophisticated transaction manager with the following features:

The transaction recovery feature depends on a transaction log, which records the status of all pending transactions in persistent storage.

Normally, the Geronimo transaction manager is accessed indirectly—for example, through the JTA wrapper layer or through the Spring wrapper layer. But if you need to access Geronimo directly, the following interface is also exposed as an OSGi service:

The implementation of the transaction log is provided by HOWL, which is a high speed persistent logger that is optimized for XA transaction logs.

Normally, it is recommended that application bundles access the transaction service through the JTA interface. To use the transaction service in a JTA-based application bundle, import the relevant JTA service as an OSGi service and use the JTA service to begin, commit, or rollback transactions.

If you have already implemented an application bundle using the Spring transaction API, you might find it more convenient to access the transaction service through the Spring API (represented by the PlatformTransactionManager Java interface). This means that you are able to deploy the same source code either in a pure Spring container or in an OSGi container, by changing only the configuration snippet that obtains a reference to the transaction service.

The following specifications are relevant to the transaction architecture in Fuse ESB Enterprise: