Java Transaction API

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The Java Transaction API (JTA), one of the Java Enterprise Edition (Java EE) APIs, enables distributed transactions to be done across multiple X/Open XA resources in a Java environment. JTA is a specification developed under the Java Community Process as JSR 907. JTA provides for:

X/Open XA architecture[edit]

In the X/Open XA architecture, a transaction manager or transaction processing monitor (TP monitor) coordinates the transactions across multiple resources such as databases and message queues. Each resource has its own resource manager. The resource manager typically has its own API for manipulating the resource, for example the JDBC API to work with relational databases. In addition, the resource manager allows a TP monitor to coordinate a distributed transaction between its own and other resource managers. Finally, there is the application which communicates with the TP monitor to begin, commit or rollback the transactions. The application also communicates with the individual resources using their own API to modify the resource.

JTA implementation of the X/Open XA architecture[edit]

The JTA API consists of classes in two Java packages:

The JTA is modelled on the X/Open XA architecture, but it defines two different APIs for demarcating transaction boundaries. It distinguishes between an application server such as an EJB server and an application component. It provides an interface, javax.transaction.TransactionManager, that is used by the application server itself to begin, commit and rollback the transactions. It provides a different interface, the javax.transaction.UserTransaction, that is used by general client code such as a servlet or an EJB to manage the transactions.

The JTA architecture requires that each resource manager must implement the javax.transaction.xa.XAResource interface in order to be managed by the TP monitor. As stated previously, each resource will have its own specific API, for instance:

Java Transaction API[edit]

The Java Transaction API consists of three elements: a high-level application transaction demarcation interface, a high-level transaction manager interface intended for an application server, and a standard Java mapping of the X/Open XA protocol intended for a transactional resource manager.

UserTransaction interface[edit]

The javax.transaction.UserTransaction interface provides the application the ability to control transaction boundaries programmatically. This interface may be used by Java client programs or EJB beans.

The UserTransaction.begin() method starts a global transaction and associates the transaction with the calling thread. The transaction-to-thread association is managed transparently by the Transaction Manager.

Support for nested transactions is not required. The UserTransaction.begin method throws the NotSupportedException when the calling thread is already associated with a transaction and the transaction manager implementation does not support nested transactions.

Transaction context propagation between application programs is provided by the underlying transaction manager implementations on the client and server machines. The transaction context format used for propagation is protocol dependent and must be negotiated between the client and server hosts. For example, if the transaction manager is an implementation of the JTS specification, it will use the transaction context propagation format as specified in the CORBA OTS 1.1 specification. Transaction propagation is transparent to application programs..

UserTransaction support in EJB server[edit]

EJB servers are required to support the UserTransaction interface for use by EJB beans with the BEAN value in the javax.ejb.TransactionManagement annotation (this is called bean-managed transactions or BMT). The UserTransaction interface is exposed to EJB components through either the EJBContext interface using the getUserTransaction method, or directly via injection using the general @Resource annotation. Thus, an EJB application does not interface with the Transaction Manager directly for transaction demarcation; instead, the EJB bean relies on the EJB server to provide support for all of its transaction work as defined in the Enterprise JavaBeans Specification. (The underlying interaction between the EJB Server and the TM is transparent to the application; the burden of implementing transaction management is on the EJB container and server provider.[1])

The code sample below illustrates the usage of UserTransaction via bean-managed transactions in an EJB session bean:

@Stateless
@TransactionManagement(BEAN)
public class ExampleBean {
 
    @Resource
    private UserTransaction utx;
 
    public void foo() {
        // start a transaction
        utx.begin();
 
        // Do work
 
        // Commit it
        utx.commit();
    }
}

Alternatively, the UserTransaction can be obtained from the SessionContext:

@Stateless
@TransactionManagement(BEAN)
public class ExampleBean {
 
    @Resource
    private SessionContext ctx;
 
    public void foo() {
        UserTransaction utx = ctx.getUserTransaction();
 
        // start a transaction
        utx.begin();
 
        // Do work
 
        // Commit it
        utx.commit();
    }
}

Note though that in the example above if the @TransactionManagement(BEAN) annotation is omitted, a JTA transaction is automatically started whenever foo() is called and is automatically committed or rolled back when foo() is exited. Making use of a UserTransaction is thus not necessary in EJB programming, but might be needed for very specialized code.

UserTransaction support in JNDI[edit]

The UserTransaction should be available under java:comp/UserTransaction (if a JTA implementation is installed in the environment).

Open source JTA implementations[edit]

There exist a number of active (as of September 2010) open source JTA implementations.

JBossTS[edit]

JBossTS, formerly known as Arjuna Transaction Service, comes with a very robust implementation, which supports both the JTA and JTS APIs. JBossTS comes with a recovery service, which could be run as a separate process from your application processes. JBossTS is the default transaction manager for JBoss AS. It does not support out-of-the box integration with the Spring framework, but it is easy to integrate.

Atomikos TransactionsEssentials[edit]

Atomikos TransactionsEssentials's documentation and literature on the internet show that it is a production quality implementation, which also supports recovery and some exotic features beyond the JTA API. Atomikos provides out-of-the-box Spring integration along with some nice examples. It also provides support for pooled connections for both database and JMS resources.

Bitronix JTA[edit]

Bitronix claims to support transaction recovery as well as or even better than some of the commercial products. Bitronix also provides connection pooling and session pooling out of the box.

See also[edit]

References[edit]

External links[edit]