Apache Camel: JPA

JPA Component

The jpa component enables you to store and retrieve Java objects from persistent storage using EJB 3's Java Persistence Architecture (JPA), which is a standard interface layer that wraps Object/Relational Mapping (ORM) products such as OpenJPA, Hibernate, TopLink, and so on.

Sending to the endpoint

You can store a Java entity bean in a database by sending it to a JPA producer endpoint. The body of the In message is assumed to be an entity bean (that is, a POJO with an @Entity annotation on it).

If the body does not contain an entity bean, put a Message Translator in front of the endpoint to perform the necessary conversion first.

Consuming from the endpoint

Consuming messages from a JPA consumer endpoint removes (or updates) entity beans in the database. This allows you to use a database table as a logical queue: consumers take messages from the queue and then delete/update them to logically remove them from the queue.

If you do not wish to delete the entity bean when it has been processed, you can specify consumeDelete=false on the URI. This will result in the entity being processed each poll.

If you would rather perform some update on the entity to mark it as processed (such as to exclude it from a future query) then you can annotate a method with @Consumed which will be invoked on your entity bean when the entity bean is consumed.

URI format

jpa:[entityClassName][?options]

For sending to the endpoint, the entityClassName is optional. If specified, it helps the Type Converter to ensure the body is of the correct type.

For consuming, the entityClassName is mandatory.

You can append query options to the URI in the following format, ?option=value&option=value&...

Options

Name	Default Value	Description
`entityType`	entityClassName	Overrides the entityClassName from the URI.
`persistenceUnit`	`camel`	The JPA persistence unit used by default.
`consumeDelete`	`true`	JPA consumer only: If `true`, the entity is deleted after it is consumed; if `false`, the entity is not deleted.
`consumeLockEntity`	`true`	JPA consumer only: Specifies whether or not to set an exclusive lock on each entity bean while processing the results from polling.
`flushOnSend`	`true`	JPA producer only: Flushes the EntityManager after the entity bean has been persisted.
`maximumResults`	`-1`	JPA consumer only: Set the maximum number of results to retrieve on the Query.
`transactionManager`	`null`	Camel 1.6.1/2.0: Specifies the transaction manager to use. If none provided, Camel will use a `JpaTransactionManager` by default. Can be used to set a JTA transaction manager (for integration with an EJB container).
`consumer.delay`	`500`	JPA consumer only: Delay in milliseconds between each poll.
`consumer.initialDelay`	`1000`	JPA consumer only: Milliseconds before polling starts.
`consumer.userFixedDelay`	`false`	JPA consumer only: Set to `true` to use fixed delay between polls, otherwise fixed rate is used. See ScheduledExecutorService in JDK for details.
`maxMessagesPerPoll`	`0`	Camel 2.0: JPA consumer only: An integer value to define the maximum number of messages to gather per poll. By default, no maximum is set. Can be used to avoid polling many thousands of messages when starting up the server. Set a value of 0 or negative to disable.
`consumer.query`		JPA consumer only: To use a custom query when consuming data.
`consumer.namedQuery`		JPA consumer only: To use a named query when consuming data.
`consumer.nativeQuery`		JPA consumer only: To use a custom native query when consuming data.

Message Headers

Camel adds the following message headers to the exchange:

Header	Type	Description
`CamelJpaTemplate`	`JpaTemplate`	Camel 2.0: The `JpaTemplate` object that is used to access the entity bean. You need this object in some situations, for instance in a type converter or when you are doing some custom processing.

Configuring EntityManagerFactory

You can configure the JPA component to use a specific EntityManagerFactory instance. For example, you can instantiate a JPA component that references the myEMFactory entity manager factory, as follows:

<bean id="jpa" class="org.apache.camel.component.jpa.JpaComponent">
   <property name="entityManagerFactory" ref="myEMFactory"/>
</bean>

Configuring TransactionManager

You can specify the TransactionManager instance used by the JPA component. For example, you can instantiate a JPA component that references the myTransactionManager transaction manager, as follows:

<bean id="jpa" class="org.apache.camel.component.jpa.JpaComponent">
   <property name="entityManagerFactory" ref="myEMFactory"/>
   <property name="transactionManager" ref="myTransactionManager"/>
</bean>

Example

See Tracer Example for an example using JPA to store traced messages into a database.

JPA Component

Sending to the endpoint

Consuming from the endpoint

URI format

Options

Message Headers

Configuring EntityManagerFactory

Configuring TransactionManager

Example

See Also

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