Appendix B - e-Reading Library

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Appendix B. State and Sequence Diagrams

B.1 Entity Beans
B.2 Session Beans

This appendix contains state and sequence diagrams for all the bean types discussed in this book: container-managed and bean-managed entity beans, stateless and stateful session beans, and message-driven beans. Although standard Unified Modeling Language (UML) is used in these diagrams, some extensions were required to model EJB runtime characteristics. In the state diagrams, for example, callback methods and class instantiation operations are shown as part of the transition event.

In the sequence diagrams, container-provided classes such as the container itself, the EJB object, and the EJB home are shown as separate classes but are also boxed together. Messages sent from classes in the container system box are considered to be sent from the container system as a whole, not necessarily from the specific container-provided class. This generalization is necessary because the container's interaction with the bean is characterized by these classes but differs from one vendor's implementation to the next. The exact source of the message is immaterial, as long as you realize that the container system sent it.

B.1 Entity Beans

B.1.1 Life Cycle State Diagram of the Entity Bean

Figure B-1. Life-cycle state diagram of the entity bean

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B.1.2 Sequence Diagrams for Container-Managed Persistence

Figure B-2. Creation and removal in container-managed persistence

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Figure B-3. Activation and synchronization in container-managed persistence

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B.1.3 Sequence Diagrams for Bean-Managed Persistence

Figure B-4. Creation and removal in bean-managed persistence

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Figure B-5. Activation and synchronization in bean-managed persistence

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Table B-1 summarizes the operations an entity bean is allowed to perform in various stages of its life cycle. The allowed operations are the same for EJB 2.0 and 1.1, except for the EntityContext methods getEJBLocalHome() and getEJBLocalObject() and the operations allowed for ejbHome() methods, which are specific to EJB 2.0.

Table B-1. Allowed operations for entity beans
Method	Allowed operations
`setEntityContext()` `unsetEntityContext()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` JNDI ENC contexts: Properties: `java:comp/env`
`ejbCreate()` `ejbFind()` `ejbHome()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getRollbackOnly()` `setRollbackOnly()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`
`ejbPostCreate()` `ejbLoad()` `ejbStore()` `ejbRemove()` Business methods	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole() getRollbackOnly()` `setRollbackOnly()` `getEJBObject()` `getEJBLocalObject()` `getPrimaryKey()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`
`ejbActivate()` `ejbPassivate()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getEJBObject()` `getEJBLocalObject()` `getPrimaryKey()` JNDI ENC contexts: Properties: `java:comp/env`

Note that entity beans can never access the EJBContext.getUserTransaction() method, because entity beans are not allowed to manage their own transactions. Only session beans can access this method.

B.2 Session Beans

B.2.1 Stateless Session Beans

Figure B-6. Life-cycle state diagram of the stateless session bean

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Figure B-7. Creation and removal of stateless session beans

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Table B-2 summarizes the operations that are legal for a stateless session bean. The allowed operations are the same for both EJB 2.0 and 1.1, except for the SessionContext methods getEJBLocalHome() and getEJBLocalObject(), which are specific to EJB 2.0.

Table B-2. Allowed operations for stateless session beans
Method	Allowed operations
	Container-managed transactions	Bean-managed transactions
`ejbCreate()` `ejbRemove()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getEJBObject()` `getEJBLocalObject()` `getUserTransaction()` JNDI ENC contexts: Properties: `java:comp/env`
Business methods	`EntityContext` methods: `getEJHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getRollbackOnly()` `setRollbackOnly()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`	`EntityContext` methods: `getEJHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getEJBObject()` `getEJBLocalObject()` `getUserTransaction()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`
`ejbActivate()` `ejbPassivate()`	Not supported (stateless beans do not use these methods)	Not supported (stateless beans do not use these methods)

B.2.2 Stateful Session Beans

Figure B-8. Life-cycle state diagram of the stateful session bean

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Figure B-9. Life cycle of a stateful session bean with the SessionSynchronization interface

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Figure B-10. Creation and removal of stateful session beans

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Figure B-11. Activation process of stateful session beans

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Figure B-12. Transaction notification in SessionSynchronization session beans

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Table B-3 summarizes the operations that are legal for a stateful session bean. The allowed operations are the same for both EJB 2.0 and 1.1, except for the SessionContext methods getEJBLocalHome() and getEJBLocalObject(), which are specific to EJB 2.0.

Table B-3. Allowed operations for stateful session beans
Method	Allowed operations
	Container-managed transactions	Bean-managed transactions
`setSessionContext()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` JNDI ENC contexts: Properties: `java:comp/env`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` JNDI ENC contexts: Properties: `java:comp/env`
`ejbCreate()` `ejbRemove()` `ejbActivate()` `ejbPassivate()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getEJBObject()` `getEJBLocalObject()` `getUserTransaction()` JNDI ENC contexts: Properties: `java:comp/ env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`
Business methods	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getRollbackOnly()` `setRollbackOnly()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`	`EntityContext` methods: `getEJHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getEJBObject()` `getEJBLocalObject()` `getUserTransaction()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`
`afterBegin()` `beforeCompetion()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getRollbackOnly()` `setRollbackOnly()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env` Resource managers: `java:comp/env/jdbc` EJB references: `java:comp/env/ejb`	Not supported (bean-managed transaction beans cannot implement the `SessionSynchronization` interface)
`afterCompletion()`	`EntityContext` methods: `getEJBHome()` `getEJBLocalHome()` `getCallerPrincipal()` `isCallerInRole()` `getEJBObject()` `getEJBLocalObject()` JNDI ENC contexts: Properties: `java:comp/env`	Not supported (bean-managed transaction beans cannot implement the `SessionSynchronization` interface)

B.2.3 Message-Driven Beans

Figure B-13. Message-driven bean life-cycle state diagram

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Figure B-14. Message-driven bean sequence diagram

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B.2.4 Interactions Between Exceptions and Transactions

Table B-4 summarizes what happens to a transaction if an exception is thrown while the transaction is in process.

Table B-4. Exception summary for session and entity beans
Transaction scope	Transaction type attributes	Exception thrown	Container's action	Client's view
Client-initiated transaction. The transaction is started by the client (application or EJB) and is propagated to the enterprise bean method.	transaction-type = Container transaction-attribute = `Required` \| `Mandatory` \| `Supports`	Application exception	If the EJB invoked `setRollbackOnly()`, mark the client's transaction for rollback. Rethrow the application exception.	Receives the application exception. The client's transaction may or may not have been marked for rollback.
		System exception	Mark the client's transaction for rollback. Log the error. Discard the instance. Rethrow the JTA `TransactionRolledbackException` to remote clients or the `javax.ejb.TransactionRolledbackLocalException` to EJB 2.0 local clients.	Remote clients receive the JTA `TransactionRolledbackException`; local clients receive the `javax.ejb.TransactionRolledbackLocalException`. The client's transaction has been rolled back.
Container-initiatedtransaction. The transaction started when the EJB's method was invoked and will end when the method completes.	transaction-type = Container transaction-attribute = `Required` \| `RequiresNew`	Application exception	If the EJB invoked `setRollbackOnly()`, roll back the transaction and rethrow the application exception. If the EJB did not explicitly roll back the transaction, attempt to commit the transaction and rethrow the application exception.	Receives the application exception. The EJB's transaction may or may not have been rolled back. The client's transaction is not affected.
		System exception	Roll back the transaction. Log the error. Discard the instance. Rethrow the `RemoteException` to remote clients or the `EJBException` to EJB 2.0 local clients.	Remote clients receive the `RemoteException`; local EJB 2.0 clients receive the `EJBException`. The EJB's transaction was rolled back. The client's transaction may or may not be marked for rollback, depending on the vendor.
The bean is not part of a transaction. The EJB was invoked but does not propagate the client's transaction and does not start its own transaction.	transaction-type = Container transaction-attribute = `Never` \| `NotSupported` \| `Supports` \|	Application exception	Rethrow the application exception.	Receives the application exception. The client's transaction is not affected.
		System exception	Log the error. Discard the instance. Rethrow the `RemoteException` to remote clients or the `EJBException` to EJB 2.0 local clients.	Remote clients receive the `RemoteException`; local EJB 2.0 clients receive the `EJBException`. The client's transaction may or may not be marked for rollback, depending on the vendor.
Bean-managed transaction. The stateful or stateless session EJB uses the `EJBContext` to explicitly manage its own transaction.	transaction-type = Bean transaction-attribute = Bean-managed transaction EJBs do not use transaction attributes.	Application exception	Rethrow the application exception.	Receives the application exception. The client's transaction is not affected.
		System exception	Roll back the transaction. Log the error. Discard the instance. Rethrow the `RemoteException` to remote clients or the `EJBException` to EJB 2.0 local clients.	Remote clients receive the `RemoteException`; local EJB 2.0 clients receive the `EJBException`. The client's transaction is not affected.

Table B-5 summarizes the interactions between different types of exceptions and transactions in message-driven beans.

Table B-5. Exception summary for message-driven beans
Transaction scope	Transaction type attributes	Exception thrown	Container's action
Container-initiated transaction. The transaction started before the `onMessage()` method was invoked and will end when the method completes.	transaction-type = Container transaction-attribute = `Required`	System exception	Roll back the transaction. Log the error. Discard the instance.
Container-initiated transaction. No transaction was started.	transaction-type = Container transaction-attribute = `NotSupported`	System exception	Log the error. Discard the instance.
Bean-managed transaction. The message-driven bean uses the `EJBContext` to explicitly manage its own transaction.	transaction-type = Bean transaction-attribute = Bean-managed transaction EJBs do not use transaction attributes.	System exception	Roll back the transaction. Log the error. Discard the instance.

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