[CONF] Apache Camel: JPA (page edited)

confluence Tue, 23 Jun 2009 22:33:34 -0700

Page Edited : CAMEL : JPA

JPA has been edited by Claus Ibsen (Jun 23, 2009).

Content:

JPA Component

The jpa: component allows you to work with databases using JPA (EJB 3 Persistence) such as for working with OpenJPA, Hibernate, TopLink to work with relational databases.

Sending to the endpoint

Sending POJOs to the JPA endpoint inserts entities into the database. The body of the message is assumed to be an entity bean (i.e. a POJO with an @Entity annotation on it).

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

Consuming from the endpoint

Consuming messages removes (or updates) entities 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 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 is used to help use the Type Converter to ensure the body is of the correct type.

For consuming the entityClassName is mandatory.

Options

Name	Default Value	Description
entityType	entityClassName	Is the provided entityClassName from the URI
persistenceUnit	camel	the JPA persistence unit used by default
consumeDelete	true	Option for JpaConsumer only. Enables / disables whether or not the entity is deleted after it is consumed.
consumeLockEntity	true	Option for JpaConsumer only. Enables / disables whether or not to use exclusive locking of each entity while processing the results from the pooling.
flushOnSend	true	Option for JpaProducer only. Flushes the EntityManager after the entity beans has been persisted.
maximumResults	-1	Option for JpaConsumer only. Set the maximum number of results to retrieve on the Query.
transactionManager	null	Camel 1.6.1/2.0: Sets the transaction manager to use. If none provided Camel will default use `JpaTransactionManager`. Can be used to set a JTA transaction manager.
consumer.delay	500	Option for JpaConsumer only. Delay in millis between each poll.
consumer.initialDelay	1000	Option for JpaConsumer only. Millis before polling starts.
consumer.userFixedDelay	false	Option for JpaConsumer only. true to use fixed delay between pools, otherwise fixed rate is used. See ScheduledExecutorService in JDK for details.
maxMessagesPerPoll	0	Camel 2.0: Option for JpaConsumer only. An integer to define a maximum messages to gather per poll. By default no maximum is set. Can be used to set a limit of e.g. 1000 to avoid when starting up the server that there are thousands of files. Set a value of 0 or negative to disabled it.

Message Headers

Camel will add the following message headers to the Exchange

Header	Type	Description
CamelJpaTemplate	JpaTemplate	Camel 2.0: The JpaTemplate object used to access the entity with. Allows you to get hold on it in case you need it in some situations, for instance in a type converter or when you do some custom processing.

Configuring EntityManagerFactory

You can configure the EntityManagerFactory to use on the JpaComponent itself. For instance in Spring XML:

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

Configuring TransactionManager

You can configure the TransactionManager to use on the JpaComponent itself. For instance in Spring XML:

<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.