Entity Providers

Entity providers provide access to entities persisted in a data store. They are essentially wrappers over a JPA entity manager, adding optimizations and other features important when binding persistent data to a user interface.

The choice and use of entity providers is largely invisible if you create your JPAContainer instances with the JPAContainerFactory, which hides such details.

JPAContainer entity providers can be customized, which is necessary for some purposes. Entity providers can be Enterprise JavaBeans (EJBs), which is useful when you use them in a Java EE application server.

Built-In Entity Providers

JPAContainer includes various kinds of built-in entity providers: caching and non-caching, read-write and read-only, and batchable.

Caching is useful for performance, but takes some memory for the cache and makes the provider stateful. Batching, that is, running updates in larger batches, can also enhance performance and be used together with caching. It is stateless, but doing updates is a bit more complex than otherwise.

Using a read-only container is preferable if read-write capability is not needed.

All built-in providers are local in the sense that they provide access to entities using a local JPA entity manager.

The CachingMutableLocalEntityProvider is usually recommended as the first choise for read-write access and CachingLocalEntityProvider for read-only access.

LocalEntityProvider

A read-only, lazy loading entity provider that does not perform caching and reads its data directly from an entity manager.

You can create the provider with makeNonCachedReadOnly() method in JPAContainerFactory.

MutableLocalEntityProvider

Extends LocalEntityProvider with write support. All changes are directly sent to the entity manager.

Transactions can be handled either internally by the provider, which is the default, or by the container. In the latter case, you can extend the class and annotate it, for example, as described in Built-In Entity Providers.

The provider can notify about updates to entities through the EntityProviderChangeNotifier interface.

BatchableLocalEntityProvider

A simple non-caching implementation of the BatchableEntityProvider interface. It extends MutableLocalEntityProvider and simply passes itself to the batchUpdate() callback method. This will work properly if the entities do not contain any references to other entities that are managed by the same container.

CachingLocalEntityProvider

A read-only, lazy loading entity provider that caches both entities and query results for different filter/sortBy combinations. When the cache gets full, the oldest entries in the cache are removed. The maximum number of entities and entity IDs to cache for each filter/sortBy combination can be configured in the provider. The cache can also be manually flushed. When the cache grows full, the oldest items are removed.

You can create the provider with makeReadOnly() method in JPAContainerFactory.

CachingMutableLocalEntityProvider

Just like CachingLocalEntityProvider, but with read-write access. For read access, caching works just like in the read-only provider. When an entity is added or updated, the cache is flushed in order to make sure the added or updated entity shows up correctly when using filters and/or sorting. When an entity is removed, only the filter/sortBy-caches that actually contain the item are flushed.

This is perhaps the most commonly entity provider that you should consider using for most tasks. You can create it with the make() method in JPAContainerFactory.

CachingBatchableLocalEntityProvider

This provider supports making updates in batches. You need to implement a BatchUpdateCallback that does all the updates and execute the batch by calling batchUpdate() on the provider.

The provider is an extension of the CachingMutableLocalEntityProvider that implements the BatchableEntityProvider interface. This will work properly if the entities do not contain any references to other entities that are managed by the same container.

You can create the provider with makeBatchable() method in JPAContainerFactory.

Using JNDI Entity Providers in JEE6 Environment

JPAContainer 2.0 introduced a new set of entity providers specifically for working in a JEE6 environment. In a JEE environment, you should use an entity manager provided by the application server and, usually, JTA transactions instead of transactions provided by JPA. Entity providers in com.vaadin.addon.jpacontainer.provider.jndijta package work mostly the same way as the normal providers discussed earlier, but use JNDI lookups to get reference to an EntityManager and to a JTA transaction.

The JNDI providers work with almost no special configuration at all. The JPAContainerFactory has factory methods for creating various JNDI provider types. The only thing that you commonly need to do is to expose the EntityManager to a JNDI address. By default, the JNDI providers look for the EntityManager from " java:comp/env/persistence/em". This can be done with the following snippet in web.xml or with similar configuration with annotations.

<persistence-context-ref>
  <persistence-context-ref-name>
    persistence/em
  </persistence-context-ref-name>
  <persistence-unit-name>MYPU</persistence-unit-name>
</persistence-context-ref>

The " MYPU" is the identifier of your persistence unit defined in your persistence.xml file.

If you choose to annotate your servlets (instead of using the web.xml file as described above), you can simply add the following annotation to your servlet.

@PersistenceContext(name="persistence/em",unitName="MYPU")

If you wish to use another address for the persistence context, you can define them with the setJndiAddresses() method. You can also define the location for the JTA UserTransaction, but that should be always accessible from " java:comp/UserTransaction" by the JEE6 specification.

Entity Providers as Enterprise Beans

Entity providers can be Enterprise JavaBeans (EJB). This may be useful if you use JPAContainer in a Java EE application server. In such case, you need to implement a custom entity provider that allows the server to inject the entity manager.

For example, if you need to use Java Transaction API (JTA) for JPA transactions, you can implement such entity provider as follows. Just extend a built-in entity provider of your choise and annotate the entity manager member as @PersistenceContext. Entity providers can be either stateless or stateful session beans. If you extend a caching entity provider, it has to be stateful.

@Stateless
@TransactionManagement
public class MyEntityProviderBean extends
    MutableLocalEntityProvider<MyEntity> {

    @PersistenceContext
    private EntityManager em;

    protected LocalEntityProviderBean() {
        super(MyEntity.class);
        setTransactionsHandledByProvider(false);
    }

    @Override
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    protected void runInTransaction(Runnable operation) {
        super.runInTransaction(operation);
    }

    @PostConstruct
    public void init() {
        setEntityManager(em);
        /*
         * The entity manager is transaction-scoped, which means
         * that the entities will be automatically detached when
         * the transaction is closed. Therefore, we do not need
         * to explicitly detach them.
         */
        setEntitiesDetached(false);
    }
}

If you have more than one EJB provider, you might want to create an abstract super class of the above and only define the entity type in implementations. You can implement an entity provider as a managed bean in Spring Framefork the same way.