[[jms-using]]
= Using Spring JMS

This section describes how to use Spring's JMS components.


[[jms-jmstemplate]]
== Using `JmsTemplate`

The `JmsTemplate` class is the central class in the JMS core package. It simplifies the
use of JMS, since it handles the creation and release of resources when sending or
synchronously receiving messages.

Code that uses the `JmsTemplate` needs only to implement callback interfaces that give them
a clearly defined high-level contract. The `MessageCreator` callback interface creates a
message when given a `Session` provided by the calling code in `JmsTemplate`. To
allow for more complex usage of the JMS API, `SessionCallback` provides the
JMS session, and `ProducerCallback` exposes a `Session` and
`MessageProducer` pair.

The JMS API exposes two types of send methods, one that takes delivery mode, priority,
and time-to-live as Quality of Service (QOS) parameters and one that takes no QOS
parameters and uses default values. Since `JmsTemplate` has many send methods,
setting the QOS parameters have been exposed as bean properties to
avoid duplication in the number of send methods. Similarly, the timeout value for
synchronous receive calls is set by using the `setReceiveTimeout` property.

Some JMS providers allow the setting of default QOS values administratively through the
configuration of the `ConnectionFactory`. This has the effect that a call to a
`MessageProducer` instance's `send` method (`send(Destination destination, Message message)`)
uses different QOS default values than those specified in the JMS specification. In order
to provide consistent management of QOS values, the `JmsTemplate` must, therefore, be
specifically enabled to use its own QOS values by setting the boolean property
`isExplicitQosEnabled` to `true`.

For convenience, `JmsTemplate` also exposes a basic request-reply operation that allows
for sending a message and waiting for a reply on a temporary queue that is created as part of
the operation.

IMPORTANT: Instances of the `JmsTemplate` class are thread-safe, once configured. This is
important, because it means that you can configure a single instance of a `JmsTemplate`
and then safely inject this shared reference into multiple collaborators. To be
clear, the `JmsTemplate` is stateful, in that it maintains a reference to a
`ConnectionFactory`, but this state is not conversational state.

As of Spring Framework 4.1, `JmsMessagingTemplate` is built on top of `JmsTemplate`
and provides an integration with the messaging abstraction -- that is,
`org.springframework.messaging.Message`. This lets you create the message to
send in a generic manner.


[[jms-connections]]
== Connections

The `JmsTemplate` requires a reference to a `ConnectionFactory`. The `ConnectionFactory`
is part of the JMS specification and serves as the entry point for working with JMS. It
is used by the client application as a factory to create connections with the JMS
provider and encapsulates various configuration parameters, many of which are
vendor-specific, such as SSL configuration options.

When using JMS inside an EJB, the vendor provides implementations of the JMS interfaces
so that they can participate in declarative transaction management and perform pooling
of connections and sessions. In order to use this implementation, Jakarta EE containers
typically require that you declare a JMS connection factory as a `resource-ref` inside
the EJB or servlet deployment descriptors. To ensure the use of these features with the
`JmsTemplate` inside an EJB, the client application should ensure that it references the
managed implementation of the `ConnectionFactory`.

[[jms-caching-resources]]
=== Caching Messaging Resources

The standard API involves creating many intermediate objects. To send a message, the
following 'API' walk is performed:

[literal]
[subs="verbatim,quotes"]
----
ConnectionFactory->Connection->Session->MessageProducer->send
----

Between the `ConnectionFactory` and the `Send` operation, three intermediate
objects are created and destroyed. To optimize the resource usage and increase
performance, Spring provides two implementations of `ConnectionFactory`.

[[jms-connection-factory]]
=== Using `SingleConnectionFactory`

Spring provides an implementation of the `ConnectionFactory` interface,
`SingleConnectionFactory`, that returns the same `Connection` on all
`createConnection()` calls and ignores calls to `close()`. This is useful for testing and
standalone environments so that the same connection can be used for multiple
`JmsTemplate` calls that may span any number of transactions. `SingleConnectionFactory`
takes a reference to a standard `ConnectionFactory` that would typically come from JNDI.

[[jdbc-connection-factory-caching]]
=== Using `CachingConnectionFactory`

The `CachingConnectionFactory` extends the functionality of `SingleConnectionFactory`
and adds the caching of `Session`, `MessageProducer`, and `MessageConsumer` instances.
The initial cache size is set to `1`. You can use the `sessionCacheSize` property to
increase the number of cached sessions. Note that the number of actual cached sessions
is more than that number, as sessions are cached based on their acknowledgment mode,
so there can be up to four cached session instances (one for each acknowledgment mode)
when `sessionCacheSize` is set to one. `MessageProducer` and `MessageConsumer` instances
are cached within their owning session and also take into account the unique properties
of the producers and consumers when caching. MessageProducers are cached based on their
destination. MessageConsumers are cached based on a key composed of the destination, selector,
noLocal delivery flag, and the durable subscription name (if creating durable consumers).

[NOTE]
====
MessageProducers and MessageConsumers for temporary queues and topics
(TemporaryQueue/TemporaryTopic) will never be cached. Unfortunately, WebLogic JMS happens
to implement the temporary queue/topic interfaces on its regular destination implementation,
mis-indicating that none of its destinations can be cached. Please use a different connection
pool/cache on WebLogic, or customize `CachingConnectionFactory` for WebLogic purposes.
====


[[jms-destinations]]
== Destination Management

Destinations, as `ConnectionFactory` instances, are JMS administered objects that you can store
and retrieve in JNDI. When configuring a Spring application context, you can use the
JNDI `JndiObjectFactoryBean` factory class or `<jee:jndi-lookup>` to perform dependency
injection on your object's references to JMS destinations. However, this strategy
is often cumbersome if there are a large number of destinations in the application or if there
are advanced destination management features unique to the JMS provider. Examples of
such advanced destination management include the creation of dynamic destinations or
support for a hierarchical namespace of destinations. The `JmsTemplate` delegates the
resolution of a destination name to a JMS destination object that implements the
`DestinationResolver` interface. `DynamicDestinationResolver` is the default
implementation used by `JmsTemplate` and accommodates resolving dynamic destinations. A
`JndiDestinationResolver` is also provided to act as a service locator for
destinations contained in JNDI and optionally falls back to the behavior contained in
`DynamicDestinationResolver`.

Quite often, the destinations used in a JMS application are only known at runtime and,
therefore, cannot be administratively created when the application is deployed. This is
often because there is shared application logic between interacting system components
that create destinations at runtime according to a well-known naming convention. Even
though the creation of dynamic destinations is not part of the JMS specification, most
vendors have provided this functionality. Dynamic destinations are created with a user-defined name,
which differentiates them from temporary destinations, and are often
not registered in JNDI. The API used to create dynamic destinations varies from provider
to provider since the properties associated with the destination are vendor-specific.
However, a simple implementation choice that is sometimes made by vendors is to
disregard the warnings in the JMS specification and to use the method `TopicSession`
`createTopic(String topicName)` or the `QueueSession` `createQueue(String
queueName)` method to create a new destination with default destination properties. Depending
on the vendor implementation, `DynamicDestinationResolver` can then also create a
physical destination instead of only resolving one.

The boolean property `pubSubDomain` is used to configure the `JmsTemplate` with
knowledge of what JMS domain is being used. By default, the value of this property is
false, indicating that the point-to-point domain, `Queues`, is to be used. This property
(used by `JmsTemplate`) determines the behavior of dynamic destination resolution through
implementations of the `DestinationResolver` interface.

You can also configure the `JmsTemplate` with a default destination through the
property `defaultDestination`. The default destination is with send and receive
operations that do not refer to a specific destination.


[[jms-mdp]]
== Message Listener Containers

One of the most common uses of JMS messages in the EJB world is to drive message-driven
beans (MDBs). Spring offers a solution to create message-driven POJOs (MDPs) in a way
that does not tie a user to an EJB container. (See
xref:integration/jms/receiving.adoc#jms-receiving-async[Asynchronous Receipt: Message-Driven POJOs]
for detailed coverage of Spring's MDP support.) Endpoint methods can be annotated with
`@JmsListener` -- see xref:integration/jms/annotated.adoc[Annotation-driven Listener Endpoints]
for more details.

A message listener container is used to receive messages from a JMS message queue and
drive the `MessageListener` that is injected into it. The listener container is
responsible for all threading of message receipt and dispatches into the listener for
processing. A message listener container is the intermediary between an MDP and a
messaging provider and takes care of registering to receive messages, participating in
transactions, resource acquisition and release, exception conversion, and so on. This
lets you write the (possibly complex) business logic
associated with receiving a message (and possibly respond to it), and delegates
boilerplate JMS infrastructure concerns to the framework.

There are two standard JMS message listener containers packaged with Spring, each with
its specialized feature set.

* xref:integration/jms/using.adoc#jms-mdp-simple[`SimpleMessageListenerContainer`]
* xref:integration/jms/using.adoc#jms-mdp-default[`DefaultMessageListenerContainer`]

[[jms-mdp-simple]]
=== Using `SimpleMessageListenerContainer`

This message listener container is the simpler of the two standard flavors. It creates
a fixed number of JMS sessions and consumers at startup, registers the listener by using
the standard JMS `MessageConsumer.setMessageListener()` method, and leaves it up the JMS
provider to perform listener callbacks. This variant does not allow for dynamic adaption
to runtime demands or for participation in externally managed transactions.
Compatibility-wise, it stays very close to the spirit of the standalone JMS
specification, but is generally not compatible with Jakarta EE's JMS restrictions.

NOTE: While `SimpleMessageListenerContainer` does not allow for participation in externally
managed transactions, it does support native JMS transactions. To enable this feature,
you can switch the `sessionTransacted` flag to `true` or, in the XML namespace, set the
`acknowledge` attribute to `transacted`. Exceptions thrown from your listener then lead
to a rollback, with the message getting redelivered. Alternatively, consider using
`CLIENT_ACKNOWLEDGE` mode, which provides redelivery in case of an exception as well but
does not use transacted `Session` instances and, therefore, does not include any other
`Session` operations (such as sending response messages) in the transaction protocol.

IMPORTANT: The default `AUTO_ACKNOWLEDGE` mode does not provide proper reliability guarantees.
Messages can get lost when listener execution fails (since the provider automatically
acknowledges each message after listener invocation, with no exceptions to be propagated to
the provider) or when the listener container shuts down (you can configure this by setting
the `acceptMessagesWhileStopping` flag). Make sure to use transacted sessions in case of
reliability needs (for example, for reliable queue handling and durable topic subscriptions).

[[jms-mdp-default]]
=== Using `DefaultMessageListenerContainer`

This message listener container is used in most cases. In contrast to
`SimpleMessageListenerContainer`, this container variant allows for dynamic adaptation
to runtime demands and is able to participate in externally managed transactions.
Each received message is registered with an XA transaction when configured with a
`JtaTransactionManager`. As a result, processing may take advantage of XA transaction
semantics. This listener container strikes a good balance between low requirements on
the JMS provider, advanced functionality (such as participation in externally managed
transactions), and compatibility with Jakarta EE environments.

You can customize the cache level of the container. Note that, when no caching is enabled,
a new connection and a new session is created for each message receipt. Combining this
with a non-durable subscription with high loads may lead to message loss. Make sure to
use a proper cache level in such a case.

This container also has recoverable capabilities when the broker goes down. By default,
a simple `BackOff` implementation retries every five seconds. You can specify
a custom `BackOff` implementation for more fine-grained recovery options. See
{spring-framework-api}/util/backoff/ExponentialBackOff.html[`ExponentialBackOff`] for an example.

NOTE: Like its sibling (xref:integration/jms/using.adoc#jms-mdp-simple[`SimpleMessageListenerContainer`]),
`DefaultMessageListenerContainer` supports native JMS transactions and allows for
customizing the acknowledgment mode. If feasible for your scenario, This is strongly
recommended over externally managed transactions -- that is, if you can live with
occasional duplicate messages in case of the JVM dying. Custom duplicate message
detection steps in your business logic can cover such situations -- for example,
in the form of a business entity existence check or a protocol table check.
Any such arrangements are significantly more efficient than the alternative:
wrapping your entire processing with an XA transaction (through configuring your
`DefaultMessageListenerContainer` with an `JtaTransactionManager`) to cover the
receipt of the JMS message as well as the execution of the business logic in your
message listener (including database operations, etc.).

IMPORTANT: The default `AUTO_ACKNOWLEDGE` mode does not provide proper reliability guarantees.
Messages can get lost when listener execution fails (since the provider automatically
acknowledges each message after listener invocation, with no exceptions to be propagated to
the provider) or when the listener container shuts down (you can configure this by setting
the `acceptMessagesWhileStopping` flag). Make sure to use transacted sessions in case of
reliability needs (for example, for reliable queue handling and durable topic subscriptions).


[[jms-tx]]
== Transaction Management

Spring provides a `JmsTransactionManager` that manages transactions for a single JMS
`ConnectionFactory`. This lets JMS applications leverage the managed-transaction
features of Spring, as described in
xref:data-access/transaction.adoc[Transaction Management section of the Data Access chapter].
The `JmsTransactionManager` performs local resource transactions, binding a JMS
Connection/Session pair from the specified `ConnectionFactory` to the thread.
`JmsTemplate` automatically detects such transactional resources and operates
on them accordingly.

In a Jakarta EE environment, the `ConnectionFactory` pools Connection and Session instances,
so those resources are efficiently reused across transactions. In a standalone environment,
using Spring's `SingleConnectionFactory` result in a shared JMS `Connection`, with
each transaction having its own independent `Session`. Alternatively, consider the use
of a provider-specific pooling adapter, such as ActiveMQ's `PooledConnectionFactory`
class.

You can also use `JmsTemplate` with the `JtaTransactionManager` and an XA-capable JMS
`ConnectionFactory` to perform distributed transactions. Note that this requires the
use of a JTA transaction manager as well as a properly XA-configured ConnectionFactory.
(Check your Jakarta EE server's or JMS provider's documentation.)

Reusing code across a managed and unmanaged transactional environment can be confusing
when using the JMS API to create a `Session` from a `Connection`. This is because the
JMS API has only one factory method to create a `Session`, and it requires values for the
transaction and acknowledgment modes. In a managed environment, setting these values is
the responsibility of the environment's transactional infrastructure, so these values
are ignored by the vendor's wrapper to the JMS Connection. When you use the `JmsTemplate`
in an unmanaged environment, you can specify these values through the use of the
properties `sessionTransacted` and `sessionAcknowledgeMode`. When you use a
`PlatformTransactionManager` with `JmsTemplate`, the template is always given a
transactional JMS `Session`.



