Application exceptions in Java

Generate QR-Code in Java Application exceptions

An application exception is normally thrown in response to a business-logic error, as opposed to a system error. Application exceptions are always delivered directly to the client without being repackaged as an EJBException type. By default, they do not cause a transaction to roll back. In this case, the client has an opportunity to recover after an application exception is thrown. Application errors are frequently used to report validation errors in this manner. In this case, the exception is thrown before tasks are started and is clearly not the result of a subsystem failure (e.g., JDBC, JMS, Java RMI, and JNDI). The @javax.ejb.ApplicationException annotation may be used to force an application exception to roll back the transaction automatically:

package javax.ejb; @Target(TYPE) @Retention(RUNTIME) public @interface ApplicationException { boolean rollback( ) default false; }

For instance, our BankEJB makes use of an application exception to denote that a withdrawal or transfer operation cannot complete due to an insufficient balance:

/** * Exception thrown when attempting to invoke an operation that requires * more funds than are currently available */ @ApplicationException(rollback = true) public class InsufficientBalanceException extends Exception { ... }

We want the transaction to be rolled back automatically, but business logic may be able to catch InsufficientBalanceException and retry the transaction automatically (by depositing more funds first, for example). The @ApplicationException annotation can also be used on subclasses of java.lang. RuntimeException and java.rmi.RemoteException. This is useful because you may not want a thrown RuntimeException to be wrapped in an EJBException, or you may not want a particular subclass of RemoteException to roll back the exception. Table 17-1 summarizes the interactions among different types of exceptions and transactions in session and entity beans.

Table 17-1. Exception summary for session and entity beans Transaction scope Client-initiated transaction. The transaction is started by the client (application or EJB) and propagated to the enterprise bean method. Transaction type attributes transaction-type = Container transaction-attribute = Required | Mandatory |Supports Exception thrown Application exception Container s action If the EJB invoked setRoll backOnly() or the application exception is annotated with

Client s view Receives the application exception. The client s transaction may or may not have been marked for rollback.

transaction has been rolled back. Receives the application exception. The EJB s transaction may or may not have been rolled back. The client s transaction is not affected.

Container-managed transaction. The transaction started when the EJB s method was invoked and will end when the method completes.

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. System exception Roll back the transaction. Log the error. Discard the instance. Rethrow the RemoteExcep tion or EJBException.

Remote clients receive the RemoteExcep tion or EJBExcep tion. The EJB s transaction was rolled back. The client s transaction may be marked for rollback, depending on the vendor. Receives the application exception. The client s transaction is not affected.

The bean is not part of a transaction. The EJB was invoked but doesn t propagate the client s transaction and doesn t start its own transaction.

Container s action Log the error. Discard the instance. Rethrow the RemoteEx ception or EJBException.

Client s view Remote clients receive the RemoteExcep tion or EJBExcep tion. The client s transaction may or may not be marked for rollback, depending on the vendor. Receives the application exception. The client s transaction is not affected.

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.