# The JMS Bridge

Apache ActiveMQ Artemis includes a fully functional JMS message bridge.

The function of the bridge is to consume messages from a source queue or topic,
and send them to a target queue or topic, typically on a different server.

> **Note:**
>
> The JMS Bridge is not intended as a replacement for transformation and more
> expert systems such as Camel.  The JMS Bridge may be useful for fast
> transfers as this chapter covers, but keep in mind that more complex
> scenarios requiring transformations will require you to use a more advanced
> transformation system that will play on use cases that will go beyond Apache
> ActiveMQ Artemis.

The source and target servers do not have to be in the same cluster which makes
bridging suitable for reliably sending messages from one cluster to another,
for instance across a WAN, and where the connection may be unreliable.

A bridge can be deployed as a standalone application or as a web application
managed by the embedded Jetty instance bootstrapped with Apache ActiveMQ
Artemis. The source and the target can be located in the same virtual machine
or another one.

The bridge can also be used to bridge messages from other non Apache ActiveMQ
Artemis JMS servers, as long as they are JMS 1.1 compliant.

> **Note:**
>
> Do not confuse a JMS bridge with a core bridge. A JMS bridge can be used to
> bridge any two JMS 1.1 compliant JMS providers and uses the JMS API. A [core
> bridge](core-bridges.md)) is used to bridge any two Apache ActiveMQ Artemis
> instances and uses the core API. Always use a core bridge if you can in
> preference to a JMS bridge. The core bridge will typically provide better
> performance than a JMS bridge. Also the core bridge can provide *once and
> only once* delivery guarantees without using XA.

The bridge has built-in resilience to failure so if the source or target server
connection is lost, e.g. due to network failure, the bridge will retry
connecting to the source and/or target until they come back online. When it
comes back online it will resume operation as normal.

The bridge can be configured with an optional JMS selector, so it will only
consume messages matching that JMS selector

It can be configured to consume from a queue or a topic. When it consumes from
a topic it can be configured to consume using a non durable or durable
subscription

The JMS Bridge is a simple POJO so can be deployed with most frameworks, simply
instantiate the `org.apache.activemq.artemis.api.jms.bridge.impl.JMSBridgeImpl`
class and set the appropriate parameters.

## JMS Bridge Parameters

The main POJO is the `JMSBridge`. It is configurable by the parameters
passed to its constructor.

- Source Connection Factory Factory

  This injects the `SourceCFF` bean (also defined in the beans file).  This
  bean is used to create the *source* `ConnectionFactory`

- Target Connection Factory Factory

  This injects the `TargetCFF` bean (also defined in the beans file).  This
  bean is used to create the *target* `ConnectionFactory`

- Source Destination Factory Factory

  This injects the `SourceDestinationFactory` bean (also defined in the beans
  file). This bean is used to create the *source* `Destination`

- Target Destination Factory Factory

  This injects the `TargetDestinationFactory` bean (also defined in the beans
  file). This bean is used to create the *target* `Destination`

- Source User Name

  this parameter is the username for creating the *source* connection

- Source Password

  this parameter is the parameter for creating the *source* connection

- Target User Name

  this parameter is the username for creating the *target* connection

- Target Password

  this parameter is the password for creating the *target* connection

- Selector

  This represents a JMS selector expression used for consuming
  messages from the source destination. Only messages that match the
  selector expression will be bridged from the source to the target
  destination

  The selector expression must follow the [JMS selector
  syntax](https://docs.oracle.com/javaee/7/api/javax/jms/Message.html)

- Failure Retry Interval

  This represents the amount of time in ms to wait between trying to recreate
  connections to the source or target servers when the bridge has detected they
  have failed

- Max Retries

  This represents the number of times to attempt to recreate connections to the
  source or target servers when the bridge has detected they have failed. The
  bridge will give up after trying this number of times. `-1` represents 'try
  forever'

- Quality Of Service

  This parameter represents the desired quality of service mode

  Possible values are:

  - `AT_MOST_ONCE`

  - `DUPLICATES_OK`

  - `ONCE_AND_ONLY_ONCE`

  See Quality Of Service section for an explanation of these modes.

- Max Batch Size

  This represents the maximum number of messages to consume from the source
  destination before sending them in a batch to the target destination. Its value
  must `>= 1`

- Max Batch Time

  This represents the maximum number of milliseconds to wait before sending a
  batch to target, even if the number of messages consumed has not reached
  `MaxBatchSize`. Its value must be `-1` to represent 'wait forever', or `>= 1`
  to specify an actual time

- Subscription Name

  If the source destination represents a topic, and you want to consume from
  the topic using a durable subscription then this parameter represents the
  durable subscription name

- Client ID

  If the source destination represents a topic, and you want to consume from
  the topic using a durable subscription then this attribute represents the
  JMS client ID to use when creating/looking up the durable subscription

- Add MessageID In Header

  If `true`, then the original message's message ID will be appended in the
  message sent to the destination in the header `ACTIVEMQ_BRIDGE_MSG_ID_LIST`. If
  the message is bridged more than once, each message ID will be appended. This
  enables a distributed request-response pattern to be used

  > **Note:**
  >
  > when you receive the message you can send back a response using the
  > correlation id of the first message id, so when the original sender gets it
  > back it will be able to correlate it.

- MBean Server

  To manage the JMS Bridge using JMX, set the MBeanServer where the JMS Bridge
  MBean must be registered (e.g. the JVM Platform MBeanServer)

- ObjectName

  If you set the MBeanServer, you also need to set the ObjectName used to
  register the JMS Bridge MBean (must be unique)

The "transactionManager" property points to a JTA transaction manager
implementation and should be set if you need to use the 'ONCE_AND_ONCE_ONLY'
Quality of Service. Apache ActiveMQ Artemis doesn't ship with such an
implementation, but if you are running within an Application Server you can
inject the Transaction Manager that is shipped.

## Source and Target Connection Factories

The source and target connection factory factories are used to create the
connection factory used to create the connection for the source or target
server.

The configuration example above uses the default implementation provided by
Apache ActiveMQ Artemis that looks up the connection factory using JNDI. For
other Application Servers or JMS providers a new implementation may have to be
provided. This can easily be done by implementing the interface
`org.apache.activemq.artemis.jms.bridge.ConnectionFactoryFactory`.

## Source and Target Destination Factories

Again, similarly, these are used to create or lookup up the destinations.

In the configuration example above, we have used the default provided by Apache
ActiveMQ Artemis that looks up the destination using JNDI.

A new implementation can be provided by implementing
`org.apache.activemq.artemis.jms.bridge.DestinationFactory` interface.

## Quality Of Service

The quality of service modes used by the bridge are described here in more
detail.

### AT_MOST_ONCE

With this QoS mode messages will reach the destination from the source at most
once. The messages are consumed from the source and acknowledged before sending
to the destination. Therefore there is a possibility that if failure occurs
between removing them from the source and them arriving at the destination they
could be lost. Hence delivery will occur at most once.

This mode is available for both durable and non-durable messages.

### DUPLICATES_OK

With this QoS mode, the messages are consumed from the source and then
acknowledged after they have been successfully sent to the destination.
Therefore there is a possibility that if failure occurs after sending to the
destination but before acknowledging them, they could be sent again when the
system recovers. I.e. the destination might receive duplicates after a failure.

This mode is available for both durable and non-durable messages.

### ONCE_AND_ONLY_ONCE

This QoS mode ensures messages will reach the destination from the source once
and only once. (Sometimes this mode is known as "exactly once"). If both the
source and the destination are on the same Apache ActiveMQ Artemis server
instance then this can be achieved by sending and acknowledging the messages in
the same local transaction. If the source and destination are on different
servers this is achieved by enlisting the sending and consuming sessions in a
JTA transaction. The JTA transaction is controlled by a JTA Transaction Manager
which will need to be set via the settransactionManager method on the Bridge.

This mode is only available for durable messages.

> **Note:**
>
> For a specific application it may possible to provide once and only once
> semantics without using the ONCE\_AND\_ONLY\_ONCE QoS level. This can be done
> by using the DUPLICATES\_OK mode and then checking for duplicates at the
> destination and discarding them. Some JMS servers provide automatic duplicate
> message detection functionality, or this may be possible to implement on the
> application level by maintaining a cache of received message ids on disk and
> comparing received messages to them. The cache would only be valid for a
> certain period of time so this approach is not as watertight as using
> ONCE\_AND\_ONLY\_ONCE but may be a good choice depending on your specific
> application.

### Time outs and the JMS bridge

There is a possibility that the target or source server will not be available
at some point in time. If this occurs then the bridge will try `Max Retries` to
reconnect every `Failure Retry Interval` milliseconds as specified in the JMS
Bridge definition.

If you implement your own factories for looking up JMS resources then you will
have to bear in mind timeout issues.

### Examples

Please see [JMS Bridge Example](examples.md#jms-bridge) which shows how to
programmatically instantiate and configure a JMS Bridge to send messages to the
source destination and consume them from the target destination between two
standalone Apache ActiveMQ Artemis brokers.
