XAResource

XAResource is an interface defined by the X/Open XA standard that enables a resource manager to participate in a distributed transaction coordinated by a transaction manager. In Java, it is exposed as javax.transaction.xa.XAResource (and jakarta.transaction.xa.XAResource in newer specifications). Resource managers such as relational databases, message queues, or other data stores implement XAResource to participate in a global transaction across multiple resources.

Core purpose and usage: XAResource provides the contract through which a resource manager coordinates with a transaction manager to execute work as part of a global transaction. The transaction manager oversees the propagation of a single logical transaction across multiple resources and coordinates the overall commit or rollback via a two-phase commit protocol.

Key methods: The interface includes start(Xid, int flags) to associate a global transaction with the resource, end(Xid, int flags) to end work on that transaction, and prepare(Xid) to ask the resource to prepare for commit. For finalization, commit(Xid, boolean onePhase) commits the transaction (onePhase can be used to optimize when a single resource is involved), and rollback(Xid) aborts it. Additional methods include recover(int flag) to obtain in-doubt transactions, forget(Xid) to release heuristically decided transactions, isSameRM(XAResource) to compare resource managers, and setTransactionTimeout(int seconds) to configure timeouts.

Xid and exceptions: XAResource operations use Xid, a global transaction identifier, to distinguish different transactions and branches. XAException provides error codes for method outcomes (for example, outcomes of prepare). This interface is a foundational part of distributed transaction management in Java EE and Jakarta EE, implemented by many database drivers, messaging systems, and other transactional resources.