Figure 13-13 Entity bean life cycle for J2EE 12 and all bean-managed persistence in Java

Encoder QR Code ISO/IEC18004 in Java Figure 13-13 Entity bean life cycle for J2EE 12 and all bean-managed persistence
Figure 13-13 Entity bean life cycle for J2EE 12 and all bean-managed persistence
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Figure 13- 1 4
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shows the entity bean life cycle as it applies to container-managed persistence
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using J2EE 13 The addition of select methods is essentially the only difference
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Figure 13-14 Entity bean life cycle for J2EE 13 with container-managed persistence
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Entity Bean Common Scenarios
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A standard scenario for using an entity bean is for the client to act as follows:
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1 Call the javaxrmiPortableRemoteObjectnarrow( ) method to get a reference to the Home interface 2 Any home or finder method can be called at this point If you are trying to access existing d ata, the finder method will pass you back the Remote interface for the EJB instance you want In this case, the desired instance would automatically be created for you by the application server, so the next step would be skipped 3 If the instance you require is for new data you are planning to add to the database, using the Home interface reference, call the desired create method for the entity bean Both the ejbCreate and ejbPostCreate methods will be executed A reference to the Remote interface for the entity is returned 4 Invoke any number of business methods using the Remote interface reference 5 Call remove on either the Home interface or the Remote interface
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shows the code involved in the preceding scenario
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Figure 13-15 Entity bean usage scenario
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: InitialContext initCtx = new InitialContext(); Object objRef = initCtxlookup("java:comp/env/ejb/Profile"); ProfileHome profileHome = (ProfileHome)PortableRemoteObject narrow(objRef, ProfileHomeclass); Profile profileRemote = profileHomefindByPrimaryKey(username); :
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Modeling Entity Bean Relationships
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Entity beans may require other Java classes such as JavaBeans to fulfill their responsibilities and may interact with other J2EE technologies such as JavaServer Pages (JSP), servlets, and session beans to deliver enterprise application functionality This section discusses details of modeling such relationships for entity beans
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Entity Bean and Other Java Classes
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A common scenario involves an entity bean that has other Java objects as de pendent data objects A good example is an Account entity bean, which has one or more addresses associated with it (reflecting multiple account holders' addresses)
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Because a dependent data o bject cannot independently exist from the entity bean, an appropriate way to model such a relationship is via the aggregation relationship between the entity bean implementation class and the dependent data object An example is shown in
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Figure 13-16 Entity bean and dependent data object
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Another scenario requiring a relationship between an entity bean and other Java classes is the notion of a data access object discussed earlier The idea is to facilitate an easier path to CMP by encapsulating the data access logic in a class by itself This can be modeled as shown in
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Figure 13- 1 7
Figure 13-17 Entity beans and data access objects
Entity Bean and JavaBeans
One of the challenges in using entity beans is that there is a significant overhead associated with each access to the entity bean due to its remote nature Even if the bean is not located across the network, overhead is still involved as the call to access data from the entity bean must go through the container As described in the previous chapter, J2EE 13 is expected to introduce the local client approach, which will eliminate these remote calls and greatly improve on the performance in this area
Despite this improvement, there is still another fundamental mechanism that causes significant overhead for entity beans, which is the number of synchronization calls that are made to maintain the integrity of the data in the EJB instance with the underlying database
To illustrate this problem, imagine an entity bean persisting 20 different pieces of information Whenever any one of the 20 gets or sets are called, the EJB container must ensure that the entity and database are in sync, so a necessary ejbLoad or ejbStore call is made Many of these calls would be made for a typical amount of data requested from this entity bean
One strategy for addressing this issue is to use the same approach as we did with session beans That is, minimize the number of calls that need t o be made to the entity bean for a particular action This could be a good approach for some cases; however, if you have many points in your enterprise application where data from a particular EJB is needed, the performance improvement gained would not be as substantial