What are transaction attributes ? Which transaction attributes should I use in which situations?

The different Transaction Attributes are:-
Required
RequiresNew
Manadatory
Supports
Never
NotSupported

The following are some of the points to be remembered when specifying transaction attributes for Enterprise JavaBeansTM-technology based components (EJBTM):

-All methods of a session bean's remote interface (and super interfaces) must have specified transaction attributes.
-Session bean home interface methods should not have transaction attributes.
(All methods of an entity bean's remote and home interfaces (and super interfaces) must have specified transaction attributes, with the exception of: methods getEJBHome(), getHandle(), getPrimaryKey(), isIdentical() methods of the remote interface; and methods getEJBMetaData(), getHomeHandle() of the home interface.
-Use Required as the default transaction attribute, to ensure that methods are invoked within a Java Transaction API (JTA) transaction context. Required causes the enterprise bean to use existing transactional context if it exists, or to create one otherwise.

-Use RequiresNew when the results of the method must be committed regardless whether the caller's transaction succeeds. For example, a method that logs all attempted transactions, whether those transaction succeed or not, could use RequiresNew to add log entries. RequiresNew always creates a new transaction context before the method call, and commits or rolls back after the method call. Note that any existing client transaction context will be suspended until the method call returns.

-Use Supports for methods that either do not change the database (directly or indirectly); or update atomically, and it does not matter whether or not the update occurs within a transaction. Supports uses the client transaction context if it exists, or no transaction context otherwise.

-Use Mandatory when the method absolutely requires an existing transaction. Mandatory causes RemoteException to be thrown unless the client is associated with a transaction context.

-Use Never to ensure that a transactional client does not access methods that are not capable of participating in the transaction. Never causes RemoteException to be thrown if the client is associated with a transactional context.

-Use NotSupported when an enterprise bean accesses a resource manager that either does not support external transaction coordination, or is not supported by the J2EE product. In this case, the bean must have container-managed transaction demarcation, and all its methods must be marked NotSupported. NotSupported will result in the method being called outside of any transaction context, whether or not one exists.
Enterprise beans that implement interface SessionSynchronization must have either the Required, RequiresNew, or Mandatory transaction attribute.

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