Using JPA in Java

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Using JPA
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Transaction Conversation
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Persistence Context
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A short-lived conversation
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Conversation
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Transaction
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Persistence Context
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Detached Entities
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A long-lived conversation
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In short-lived conversations that do not span a transaction, the persistence context outlives the conversation lifetime Consequently, component implementations need to handle detached entities However, with longer-lived conversations, component implementations have to take special care to reattach entities to a new persistence context Suppose LoanService was conversational, with apply and updateContactInfo operations Further, for illustration purposes, assume LoanComponent implementing the service persists LoanApplication entities using JPA directly instead of DAOs If each operation was called in the context of a different transaction, LoanComponent must ensure that LoanApplication was merged with the persistence context, as shown in Listing 1110
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Persistence Merging Persistence Entities
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Listing 1110
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@Scope("CONVERSATION") public class LoanComponent implements LoanService { private EntityManager entityManager; private LoanApplication application; @PersistenceContext public void setEntityManager(EntityManager entityManager) { thisentityManager = entityManager; } public LoanResult apply(LoanRequest request) { application = new LoanApplication(); // populate the application with data from the request entityManagerpersist(application); } public updateContactInfo(Info info) { // update the application application = entityManagermerge(application); } public end() { // perform some processing } // }
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After apply is called, entityManager will be ushed and changes (that is, the new loan application) applied to the database In addition, the persistence context will be closed and the application object detached Subsequent calls to updateContact will therefore need to reattach the application object by calling EntityManagermerge() When updateContact returns, the runtime will ush and close the persistence context
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In conversational interactions, it is often desirable to extend the scope of the persistence and have it remain active for the duration of a conversation
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Extended Persistence Contexts In conversational interactions, it is often desirable to extend the scope of the persistence and have it remain active for the duration of a conversation, as opposed to the lifetime of a transaction Persistence contexts tied to the lifetime of a conversation are termed extended persistence contexts Figure 115 depicts an extended persistence context
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Using JPA
Conversation Transaction Transaction
Persistence Context
Merging persistence entities
The main bene t of extended persistence contexts is that reattachment does not need to be done This simpli es code and saves the expense of a merge operation Extended persistence contexts are speci ed by setting the type attribute of @PersistenceContext to
javaxpersistencePersistenceContextTypeEXTENDED
Listing 1111 shows how this is done Note also that the call to EntityManagermerge() from Listing 1110 has been removed because it is no longer needed
Listing 1111 An Extended Persistence Context
@Scope("CONVERSATION") public class LoanComponent implements LoanService { private EntityManager entityManager; private LoanApplication application; @PersistenceContext (type = PersistenceContextTypeEXTENDED) public void setEntityManager(EntityManager entityManager) { thisentityManager = entityManager; } public LoanResult apply(LoanRequest request) { application = new LoanApplication(); // populate the application with data from the request entityManagerpersist(application); } public updateContactInfo(Info info) {
Persistence // update the application } public end() { // perform some processing } //
If each operation (for example, apply and updateContactInfo) were invoked in different transaction contexts, the persistence context would be ushed multiple times as each transaction completed However, the persistence context would remain open Assuming the end operation was annotated with @Ends Conversation, the extended persistence context would be closed only when it was invoked Accessing the EntityManagerFactory To access EntityManagerFactory instead of an EntityManager, a component implementation can use the @PersistenceUnit annotation For example, the LoanApplicationJPADao can be rewritten to use the EntityManagerFactory, as shown in Listing 1112
Listing 1112 Injecting an EntityManagerFactory
import javaxpersistencePersistenceUnit; import orgosoaannotationsGlobalManagedTransaction; public class LoanApplicationJPADao implements LoanApplicationDao { private EntityManagerFactory emf; @PersistenceUnit(unitName="loanApp") public void setEntityManagerFactory(EntityManagerFactory emf) { thisemf = emf; } public void update(LoanApplication application){ EntityManager entityManager = emfcreateEntityManager(); entityManagerpersist(application); } }
Summary
Accessing the Hibernate API with Fabric3
At times, it is useful to be able to access the proprietary APIs of a JPA provider As an alternative to EntityManager, Fabric3 provides access to the Hibernate org hibernateSession object To utilize it, use the @PersistenceContext annotation, substituting Session for EntityManagergetDelegate(), as shown in the following excerpt:
import import import import orgosoaannotationsGlobalManagedTransaction; orghibernateSession; orgjavaxpersistenceEntityManaget; orgjavaxpersistencePersistenceContext;
@GlobalManagedTransaction public class LoanApplicationJPADao implements LoanApplicationDao { private Session session; @PersistenceContext public void setSession(EntityManager em) { thissession = (Session)emgetDelegate() } // }
Summary
This chapter has dealt with one of the most important aspects of application development: persistence In particular, we have covered how to effectively use JDBC and JPA with SCA The next chapter completes this application development picture by explaining how SCA integrates with Java EE web technologies, speci cally servlets and JSPs