Before proceeding with transactions in WebLogic Server EJB applications, you should be familiar with the concepts of the EJB transactions and its implementation with the help of sample code fragments provided for EJB applications.
Before you begin, you should read Introducing Transactions, particularly the following topics:
This document describes the Oracle WebLogic Server implementation of transactions in Enterprise JavaBeans. The information in this document supplements the Enterprise JavaBeans Specification 2.1.
Note:
Before proceeding with the rest of this chapter, you should be familiar with the contents of the EJB Specification 2.1 document, particularly the concepts and material presented in chapter Support for Transactions.
For information about implementing Enterprise JavaBeans in WebLogic Server applications, see Developing Enterprise JavaBeans, Version 2.1, for Oracle WebLogic Server.
Understand the guidelines for implementing transactions in EJB applications for WebLogic Server.
The following general guidelines apply when implementing transactions in EJB applications for WebLogic Server:
The EJB specification allows for flat transactions only. Transactions cannot be nested.
The EJB specification allows for distributed transactions that span multiple resources (such as databases) and supports the two-phase commit protocol for both EJB CMP 2.1 and EJB CMP 1.1.
Use standard programming techniques to optimize transaction processing. For example, properly demarcate transaction boundaries and complete transactions quickly.
Use a database connection from a local TxDataSource—on the WebLogic Server instance on which the EJB is running. Do not use a connection from a TxDataSource on a remote WebLogic Server instance.
Be sure to tune the EJB cache to ensure maximum performance in transactional EJB applications. See Developing Enterprise JavaBeans, Version 2.1, for Oracle WebLogic Server.
For general guidelines about the WebLogic Server Transaction Service, see Capabilities and Limitations.
Learn about the transaction attributes for container-managed and bean-managed transactions.
Transaction attributes determine how transactions are managed in EJB applications. For each EJB, the transaction attribute specifies whether transactions are demarcated by the WebLogic Server EJB container (container-managed transactions) or by the EJB itself (bean-managed transactions). The setting of the transaction-type element in the deployment descriptor determines whether an EJB is container-managed or bean-managed. See Chapter 16, "Support for Transactions," and Chapter 21, "Deployment Descriptor," in the EJB Specification 2.1, for more information about the transaction-type element.
In general, the use of container-managed transactions is preferred over bean-managed transactions because application coding is simpler. For example, in container-managed transactions, transactions do not need to be started explicitly.
WebLogic Server fully supports method-level transaction attributes as defined in Section 16.4 in the EJB Specification 2.1.
For container-managed transactions, the transaction attribute is specified in the container-transaction element in the deployment descriptor. Container-managed transactions include all entity beans and any stateful or stateless session beans with a transaction-type set to Container. For more information about these elements, see Developing Enterprise JavaBeans, Version 2.1, for Oracle WebLogic Server.
The Application Assembler can specify the following transaction attributes for EJBs and their business methods:
NotSupported
Supports
Required
RequiresNew
Mandatory
Never
For a detailed explanation about how the WebLogic Server EJB container responds to the trans-attribute setting, see section 17.6.2 in the EJB Specification 2.1 at http://www.oracle.com/technetwork/java/javaee/ejb/index.html.
The WebLogic Server EJB container automatically sets the transaction timeout if a timeout value is not defined in the deployment descriptor. The container uses the value of the Timeout Seconds configuration parameter. The default timeout value is 30 seconds.
For EJBs with container-managed transactions, the EJBs have no access to the javax.transaction.UserTransaction interface, and the entering and exiting transaction contexts must match. In addition, EJBs with container-managed transactions have limited support for the setRollbackOnly and getRollbackOnly methods of the javax.ejb.EJBContext interface, where invocations are restricted by rules specified in Sections 16.4.4.2 and 16.4.4.3 of the EJB Specification 2.1.
For bean-managed transactions, the bean specifies transaction demarcations using methods in the javax.transaction.UserTransaction interface. Bean-managed transactions include any stateful or stateless session beans with a transaction-type set to Bean. Entity beans cannot use bean-managed transactions.
For stateless session beans, the entering and exiting transaction contexts must match. For stateful session beans, the entering and exiting transaction contexts may or may not match. If they do not match, the WebLogic Server EJB container maintains associations between the bean and the non-terminated transaction.
Session beans with bean-managed transactions cannot use the setRollbackOnly and getRollbackOnly methods of the javax.ejb.EJBContext interface.
Understand usage of the term "participating in a transaction”, which is generally used when bean is invoked in container-managed transaction or bean-managed transaction.
When the EJB Specification 2.1 uses the phrase "participating in a transaction", Oracle interprets this to mean that the bean meets either of the following conditions:
The bean is invoked in a transactional context (container-managed transaction).
The bean begins a transaction using the UserTransaction API in a bean method invoked by the client (bean-managed transaction), and it does not suspend or terminate that transaction upon completion of the corresponding bean method invoked by the client.
Learn about the transaction semantics for container-managed and bean-managed transactions.
The EJB Specification 2.1 describes semantics that govern transaction processing behavior based on the EJB type (entity bean, stateless session bean, or stateful session bean) and the transaction type (container-managed or bean-managed). These semantics describe the transaction context at the time a method is invoked and define whether the EJB can access methods in the javax.transaction.UserTransaction interface. EJB applications must be designed with these semantics in mind.
For container-managed transactions, transaction semantics vary for each bean type.
Table 11-1 describes the transaction semantics for stateful session beans in container-managed transactions.
Table 11-1 Transaction Semantics for Stateful Session Beans in Container-Managed Transactions
| Method | Transaction Context at the Time the Method Was Invoked | Can Access UserTransaction Methods? |
|---|---|---|
Constructor |
Unspecified |
No |
setSessionContext() |
Unspecified |
No |
ejbCreate() |
Unspecified |
No |
ejbRemove() |
Unspecified |
No |
ejbActivate() |
Unspecified |
No |
ejbPassivate() |
Unspecified |
No |
|
Business method |
Yes or No based on transaction attribute |
No |
afterBegin() |
Yes |
No |
beforeCompletion() |
Yes |
No |
afterCompletion() |
No |
No |
Table 11-2 describes the transaction semantics for stateless session beans in container-managed transactions.
Table 11-2 Transaction Semantics for Stateless Session Beans in Container-Managed Transactions
| Method | Transaction Context at the Time the Method Was Invoked | Can Access UserTransaction Methods? |
|---|---|---|
Constructor |
Unspecified |
No |
setSessionContext() |
Unspecified |
No |
ejbCreate() |
Unspecified |
No |
ejbRemove() |
Unspecified |
No |
|
Business method |
Yes or No based on transaction attribute |
No |
Table 11-3 describes the transaction semantics for entity beans in container-managed transactions.
Table 11-3 Transaction Semantics for Entity Beans in Container-Managed Transactions
| Method | Transaction Context at the Time the Method Was Invoked | Can Access UserTransaction Methods? |
|---|---|---|
|
Constructor |
Unspecified |
No |
setEntityContext() |
Unspecified |
No |
unsetEntityContext() |
Unspecified |
No |
ejbCreate() |
Determined by transaction attribute of matching create |
No |
ejbPostCreate() |
Determined by transaction attribute of matching create |
No |
ejbRemove() |
Determined by transaction attribute of matching remove |
No |
ejbFind() |
Determined by transaction attribute of matching find |
No |
ejbActivate() |
Unspecified |
No |
ejbPassivate() |
Unspecified |
No |
ejbLoad() |
Determined by transaction attribute of business method that invoked |
No |
ejbStore() |
Determined by transaction attribute of business method that invoked |
No |
|
Business method |
Yes or No based on transaction attribute |
No |
For bean-managed transactions, the transaction semantics differ between stateful and stateless session beans. For entity beans, transactions are never bean-managed.
Table 11-4 describes the transaction semantics for stateful session beans in bean-managed transactions.
Table 11-4 Transaction Semantics for Stateful Session Beans in Bean-Managed Transactions
| Method | Transaction Context at the Time the Method Was Invoked | Can Access UserTransaction Methods? |
|---|---|---|
|
Constructor |
Unspecified |
No |
setSessionContext() |
Unspecified |
No |
ejbCreate() |
Unspecified |
Yes |
ejbRemove() |
Unspecified |
Yes |
ejbActivate() |
Unspecified |
Yes |
ejbPassivate() |
Unspecified |
Yes |
Business method |
Typically, no unless a previous method execution on the bean had completed while in a transaction context |
Yes |
afterBegin() |
Not applicable |
Not applicable |
beforeCompletion() |
Not applicable |
Not applicable |
afterCompletion() |
Not applicable |
Not applicable |
Table 11-5 describes the transaction semantics for stateless session beans in bean-managed transactions.
Table 11-5 Transaction Semantics for Stateless Session Beans in Bean-Managed Transactions
| Method | Transaction Context at the Time the Method Was Invoked | Can Access UserTransaction Methods? |
|---|---|---|
|
Constructor |
Unspecified |
No |
setSessionContext() |
Unspecified |
No |
ejbCreate() |
Unspecified |
Yes |
ejbRemove() |
Unspecified |
Yes |
|
Business method |
No |
Yes |
A stateful session bean using container-managed transactions can implement the javax.ejb.SessionSynchronization interface to provide transaction synchronization notifications.
In addition, all methods on the stateful session bean must support one of the following transaction attributes: REQUIRES_NEW, MANDATORY or REQUIRED. For more information about the javax.ejb.SessionSynchronization interface, see Section 6.5.3 in the EJB Specification 2.1.
If a bean implements SessionSynchronization, the WebLogic Server EJB container makes few callbacks to the bean during the transaction time. A synchronization cycle can occur when a registered object receives a beforeCompletion callback.
The WebLogic Server EJB container typically makes the following callbacks to the bean during transaction commit time:
afterBegin()
beforeCompletion()
afterCompletion()
The EJB container can call other beans or involve additional XA resources in the beforeCompletion method. The number of calls is limited by the beforeCompletionIterationLimit attribute. This attribute specifies how many cycles of callbacks are processed before the transaction is rolled back. A synchronization cycle can occur when a registered object receives a beforeCompletion callback and then enlists additional resources or causes a previously synchronized object to be reregistered. The iteration limit ensures that synchronization cycles do not run indefinitely.
Bean providers can specify the timeout period for transactions in EJB applications. If the duration of a transaction exceeds the specified timeout setting, then the Transaction Service rolls back the transaction automatically.
Note:
You must set the timeout before you begin() the transaction. Setting a timeout does not affect transaction transactions that have begun.
Timeouts are specified according to the transaction type:
Container-managed transactions. The Bean Provider configures the trans-timeout-seconds attribute in the weblogic-ejb-jar.xml deployment descriptor.
Bean-managed transactions. An application calls the UserTransaction.setTransactionTimeout method.
Note:
DBMS provides a DISTRIBUTED_LOCK_TIMEOUT setting, specifying the duration for which the XA transactions can hold the locks. If this is lower than the JTA timeout, the DBMS may abort the transactions.
WebLogic Server EJB applications must catch and handle specific exceptions thrown during transactions.
For detailed information about handling exceptions, see Chapter 17, "Exception Handling," in the EJB Specification 2.1.
For more information about how exceptions are thrown by business methods in EJB transactions, see the following tables in Section 17.3: Table 12 (for container-managed transactions) and Table 13 (for bean-managed transactions).
For a client's view of exceptions, see Section 17.4, particularly Section 12.4.1 (application exceptions), Section 17.4.2 (java.rmi.RemoteException), Section 17.4.2.1 (javax.transaction.TransactionRolledBackException), and Section 17.4.2.2 (javax.transaction.TransactionRequiredException).