Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Handling Exceptions

The exceptions thrown by enterprise beans fall into two categories: system and application.

A system exception indicates a problem with the services that support an application. For example, a connection to an external resource cannot be obtained, or an injected resource cannot be found. If it encounters a system-level problem, your enterprise bean should throw a `javax.ejb.EJBException`. Because the `EJBException` is a subclass of `RuntimeException`, you do not have to specify it in the `throws` clause of the method declaration. If a system exception is thrown, the EJB container might destroy the bean instance. Therefore, a system exception cannot be handled by the bean’s client program, but instead requires intervention by a system administrator.

An application exception signals an error in the business logic of an enterprise bean. Application exceptions are typically exceptions that you’ve coded yourself, such as the `BookException` thrown by the business methods of the `CartBean` example. When an enterprise bean throws an application exception, the container does not wrap it in another exception. The client should be able to handle any application exception it receives.

If a system exception occurs within a transaction, the EJB container rolls back the transaction. However, if an application exception is thrown within a transaction, the container does not roll back the transaction.

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