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Declarative transaction management in Enterprise JavaBeans
upon invocation of the method (refer to Table 14 in EJB Specification Version 2.0,
Section 17.6.2.7 Transaction attribute summary). Should the method be processed
without the presence of a global transaction context, work performed against an
external resource manager from within the method is completed using local
transaction(s). The following are specific examples of when local transactions are used
for EJB methods of an EJB with container-managed transaction demarcation:
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If the transaction attribute is set to NotSupported and the container detects that
resources were accessed.
If the transaction attribute is set to Supports and the container detects that a) the
method was not invoked from within a global transaction, and b) resources were
accessed.
If the transaction attribute is set to Never and the container detects that resources
were accessed.
Transaction attributes
EJBs that use bean-managed transaction have transaction attributes associated with
each method of the bean. The attribute value tells the container how it must manage
the transactions that involve this bean. There are six different transaction attributes that
can be associated with each method of a bean. This association is done at deployment
time by the Application Assembler or Deployer.
These attributes are:
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Required: This attribute guarantees that the work performed by the associated
method is within a global transaction context. If the caller already has a transaction
context, then the container uses the same context. If not, the container begins a new
transaction automatically. This attribute permits easy composition of multiple beans
and co-ordination of the work of all the beans using the same global transaction.
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RequiresNew: This attribute is used when the method does not want to be associated
with an existing transaction. It ensures that the container begins a new transaction.
Supports: This attribute permits the method to avoid using a global transaction. This
must only be used when a bean's method only accesses one transaction resource,
or no transaction resources, and does not invoke another enterprise bean. It is used
solely for optimization, because it avoids the cost associated with global
transactions. When this attribute is set and there is already a global transaction, the
EJB Container invokes the method and have it join the existing global transaction.
However, if this attribute is set, but there is no existing global transaction, the
Container starts a local transaction for the method, and that local transaction
completes at the end of the method.
NotSupported: This attribute also permits the bean to avoid using a global
transaction. When this attribute is set, the method must not be in a global
transaction. Instead, the EJB Container suspends any existing global transaction
and starts a local transaction for the method, and the local transaction completes at
the conclusion of the method.
Mandatory: It is recommended that this attribute not be used. Its behavior is similar to
Requires, but the caller must already have an associated transaction. If not, the
container throws a javax.transaction.TransactionRequiredException. This attribute
makes the bean less flexible for composition because it makes assumptions about
the caller's transaction.
Never: It is recommended that this attribute not be used. However, if used, the EJB
Container starts a local transaction for the method. The local transaction completes
at the conclusion of the method.
176 BES Developer’s Guide