Enterprise Bean (EJB) programming tutorials

Enterprise Beans Tutorial

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Enterprise Beans Tutorial

10 The generated SQL statements have been tested with these types of databases: Cloudscape, Oracle, and Microsoft SQL Server. You may need to edit the generated SQL statements to satisify the
requirements of your database Shared Access · Entity beans may be shared by multiple clients. Because the clients might want to change the same data,
it's important that entity beans work within transactions. · Typically, the EJB container provides transaction management. You specify the transaction attributes in
the bean's deployment descriptor. You do not have to code the transaction boundaries in the bean-- the
container marks the boundaries for you. Primary Key Each entity bean has a unique object identifier. The unique identifier, or primary key, enables the client to locate a particular entity bean. A Bean-Managed Persistence Example Entity Bean Class The entity bean class meets the requirements of every entity bean: It implements the EntityBean interface.
The class is defined as public.
The class cannot be defined as abstract or final.
It implements zero or more ejbCreate and ejbPostCreate methods.
It implements the finder methods (only for bean-managed persistence).
It implements the business methods.
It contains an empty constructor.
It does not implement the finalize method. The EntityBean Interface · The EntityBean interface extends the EnterpriseBean interface, which extends the Serializable interface. · The EntityBean interface declares a number of methods, such as ejbActivate and ejbLoad, which you
must implement in your entity bean class. The ejbCreate Method · When the client invokes a create method, the EJB container invokes the corresponding ejbCreate
method. · Typically, an ejbCreate method in an entity bean performs the following tasks: o Inserts the entity state into the database. o Initializes the instance variables. o Returns the primary key. · an enterprise bean may contain multiple ejbCreate methods · When writing an ejbCreate method for an entity bean, be sure to follow these rules: o The access control modifier must be public. o The return type must be the primary key (only for bean-managed persistence). o The arguments must be legal types for Java RMI. o The method modifier cannot be final or static. o The throws clause may include the javax.ejb.CreateException and other exceptions that are specific to your application. o An ejbCreate method usually throws a CreateException if an input parameter is invalid.