Global transactions

If an application uses two or more resources, then an external transaction manager is needed to coordinate the updates to both resource managers in a global tansaction .

Global transaction support is available to web and enterprise bean J2EE components and, with some limitation, to application client components. Enterprise bean components can be subdivided into beans that exploit container-managed transactions (CMT) or bean-managed transactions (BMT).

BMT enterprise beans, application client components, and web components can use the Java Transaction API (JTA) UserTransaction interface to define the demarcation of a global transaction. The UserTransaction interface can be obtained by a JNDI lookup of java:comp/UserTransaction or from the SessionContext object using the getUserTransaction method.. The UserTransaction is not available to the following components:

CMT enterprise beans. Any attempt by such beans to obtain the interface results in an exception in accordance with the EJB specification.

Ensure that programs that perform a JNDI lookup of the UserTransaction interface, use an InitialContext that resolves to a local implementation of the interface. Also ensure that such programs use a JNDI location appropriate for the EJB version.

Before the EJB 1.1 specification, the JNDI location of the UserTransaction interface was not specified. Each EJB container implementor defined it in an implementation-specific manner. Earlier versions of WebSphere Application Server, up to and including Version 3.5.x (without EJB 1.1), bind the UserTransaction interface to a JNDI location of jta/usertransaction. WebSphere Application Server Version 4, and later releases, bind the UserTransaction interface at the location defined by EJB 1.1, which is java:comp/UserTransaction. WebSphere Application Server, from Version 5 no longer provides the jta/usertransaction binding within Web and EJB containers to applications at a J2EE level of 1.3 or later. For example, from EJB 2.0 applications can use only the java:comp/UserTransaction location.

A web component or enterprise bean (CMT or BMT) can get the ExtendedJTATransaction interface through a lookup of java:comp/websphere/ExtendedJTATransaction . This interface provides access to the transaction identity and a mechanism to receive notification of transaction completion.