PRIMARY KEYS FOR BEAN-MANAGED PERSISTENCE in Java

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PRIMARY KEYS FOR BEAN-MANAGED PERSISTENCE
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The given primary key:
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A client can fetch the primary key of an entity bean by invoking the method of the class:
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Getting the Primary Key
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verifies the existence of the database row for the
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BEAN-MANAGED PERSISTENCE EXAMPLES
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Handling Exceptions
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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 Examples of these problems include the following: a database connection cannot be obtained, a SQL insert fails because the database is full, or a method cannot find the desired object If your enterprise bean encounters a system-level problem, it should throw a The container will wrap the in a , which it passes back to the client Because the is a subclass of the , you do not have to specify it in the 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; it requires intervention by a system administrator An application exception signals an error in the business logic of an enterprise bean There are two types of application exceptions: customized and predefined A customized exception is one that you ve coded yourself, such as the thrown by the business method of the example The package includes several predefined exceptions that are designed to handle common problems For example, an method should throw a to indicate an invalid input parameter 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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The entity bean retrieves its own primary key by calling the method of the class:
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Table 5 2 Exceptions
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Method Name
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Exception It Throws
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Table 5 2 summarizes the exceptions of the exceptions are application exceptions, except for the and the , which are system exceptions
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BEAN-MANAGED PERSISTENCE EXAMPLES
6 Container-Managed Persistence Examples
Dale Green
N entity bean with container-managed persistence offers important advantages to the bean developer First, the EJB container handles all database storage and retrieval calls Second, the container manages the relationships between the entity beans Because of these services, you don t have to code the database access calls in the entity bean Instead, you specify settings in the bean s deployment descriptor Not only does this approach save you time, but it makes the bean portable across various database servers
This chapter focuses on the source code and deployment settings for an example called , an application that features entity beans with container-managed persistence If you are unfamiliar with the terms and concepts mentioned in this chapter, please consult the section Container-Managed Persistence, page (53)