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.
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) or a collection or an array of entity beans.
If the body does not contain one of the preceding types, put a Message TranslatorMessage Translator in front of the endpoint to perform the necessary conversion first.
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.
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&...
Table 55, “URI options” lists the JPA uri options:
Table 55. URI 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
| Apache Camel 1.6.1/2.0: Specifies
the transaction manager to use. If none provided, Apache 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.useFixedDelay
|
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
| Apache 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.resultClass
| Apache Camel 2.7: JPA consumer only:
Defines the type of the returned payload (we will call
entityManager.createNativeQuery(nativeQuery,
resultClass) instead of
entityManager.createNativeQuery(nativeQuery) ).
Without this option, we will return an object array. Only has an affect
when using in conjunction with native 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. | |
usePersist
|
false
| Apache Camel 2.5: JPA producer
only: Indicates to use
entityManager.persist(entity) instead of
entityManager.merge(entity) . Note:
entityManager.persist(entity) doesn't work for
detached entities (where the EntityManager has to execute an UPDATE
instead of an INSERT query)! |
Apache Camel adds the following message header to the exchange:
Table 56. Message header options
Header | Type | Description |
---|---|---|
CamelJpaTemplate
|
JpaTemplate
| Apache 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. |
You are strongly advised to configure the JPA component to use a specific
EntityManagerFactory
instance. If you do not do so, each JpaEndpoint
will auto-create its own 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>
In Apache Camel 2.3 the
JpaComponent
will auto lookup the
EntityManagerFactory
from the Registry which means you do not need to configure this on the
JpaComponent
as shown above. You only need to do so if there is
ambiguity, in which case Camel will log a WARN.
You are strongly advised to specify the TransactionManager
instance used by the JPA
component. If you do not do so, each JpaEndpoint
will auto-create its own instance of
TransactionManager
. 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>
In Apache Camel 2.3 the
JpaComponent
will auto lookup the
TransactionManager
from the Registry which means you do not need to configure this on the
JpaComponent
as shown above. You only need to do so if there is
ambiguity, in which case Camel will log a WARN.
For consuming only selected entities, you can use the consumer.namedQuery
URI query
option. First, you have to define the named query in the JPA Entity class:
@Entity @NamedQuery(name = "step1", query = "select x from MultiSteps x where x.step = 1") public class MultiSteps { ... }
After that you can define a consumer uri like this one:
from("jpa://org.apache.camel.examples.MultiSteps?consumer.namedQuery=step1") .to("bean:myBusinessLogic");
For consuming only selected entities, you can use the consumer.query
URI query option.
You only have to define the query option:
from("jpa://org.apache.camel.examples.MultiSteps?consumer.query=select o from org.apache.camel.examples.MultiSteps o where o.step = 1") .to("bean:myBusinessLogic");
For consuming only selected entities, you can use the consumer.nativeQuery
URI query
option. You only have to define the native query option:
from("jpa://org.apache.camel.examples.MultiSteps?consumer.nativeQuery=select * from MultiSteps where step = 1") .to("bean:myBusinessLogic");
If you use the native query option, you will receive an object array in the message body.