Enterprise Bean (EJB) programming tutorials

Enterprise Beans Tutorial

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Enterprise Beans Tutorial

20 Transaction Attributes and Scope Transaction Attribute Client's Transaction Business Method's Transaction none T2 Required T1 T1 none T2 RequiresNew T1 T2 none error Mandatory T1 T1 none none NotSupported T1 none none none Supports T1 T1 none none Never T1 error Setting Transaction Attributes Because transaction attributes are stored in the deployment descriptor, they can be changed during several phases of J2EE application development: enterprise bean creation, application assembly, and
deployment. However, as an enterprise bean developer, it is your responsibility to specify the attributes when creating the bean. The attributes should be modified only by an application developer who is assembling components into larger applications. Do not expect the person who is deploying the J2EE application to specify the transaction attributes.
You can specify the transaction attributes for the entire enterprise bean or for individual methods.
If you've specified one attribute for a method and another for the bean, the attribute for the method takes precedence. When specifying attributes for individual methods, the requirements for session and entity beans vary. Session beans need the attributes defined for business methods, but do not allow them for the create
methods. Entity beans require transaction attributes for the business, create, remove, and finder methods. Rolling Back a Container-Managed Transaction There are two ways to roll back a container-managed transaction. First, if a system exception is thrown, the container will automatically roll back the transaction.
Second, by invoking the setRollbackOnly method of the EJBContext interface, the bean method instructs the container to roll back the transaction. If the bean throws an application exception,
the roll back is not automatic, but may be initiated by a call to setRollbackOnly. When the container rolls back a transaction, it always undoes the changes to data made by SQL calls within the transaction. However, only in entity beans will the container undo changes
made to instance variables. (It does so by automatically invoking the entity bean's ejbLoad
method, which loads the instance variables from the database.) When a rollback occurs, a session bean must explicitly reset any instance variables changed within the transaction. The easiest way to reset a session bean's instance variables is by implementing
the SessionSynchonization interface.