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## Chapter 33. The JMS Bridge

HornetQ 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.

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, with HornetQ standalone server or inside a JBoss AS instance. 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 HornetQ 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 (described in Chapter 36, Core Bridges) is used to bridge any two HornetQ 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

Typically, the bridge is deployed by the JBoss Micro Container via a beans configuration file. This would typically be deployed inside the JBoss Application Server and the following example shows an example of a beans file that bridges 2 destinations which are actually on the same server.

    <?xml version="1.0" encoding="UTF-8"?>

    <deployment xmlns="urn:jboss:bean-deployer:2.0">

           <bean name="JMSBridge" class="org.hornetq.api.jms.bridge.impl.JMSBridgeImpl">
               <!-- HornetQ must be started before the bridge -->
               <depends>HornetQServer</depends>
               <constructor>
                   <!-- Source ConnectionFactory Factory -->
                   <parameter>
                       <inject bean="SourceCFF"/>
                   </parameter>
                   <!-- Target ConnectionFactory Factory -->
                   <parameter>
                       <inject bean="TargetCFF"/>
                   </parameter>
                   <!-- Source DestinationFactory -->
                   <parameter>
                       <inject bean="SourceDestinationFactory"/>
                   </parameter>
                   <!-- Target DestinationFactory -->
                   <parameter>
                       <inject bean="TargetDestinationFactory"/>
                   </parameter>
                   <!-- Source User Name (no username here) -->
                   <parameter><null /></parameter>
                   <!-- Source Password (no password here)-->
                   <parameter><null /></parameter>
                   <!-- Target User Name (no username here)-->
                   <parameter><null /></parameter>
                   <!-- Target Password (no password here)-->
                   <parameter><null /></parameter>
                   <!-- Selector -->
                   <parameter><null /></parameter>
                   <!-- Failure Retry Interval (in ms) -->
                   <parameter>5000</parameter>
                   <!-- Max Retries -->
                   <parameter>10</parameter>
                   <!-- Quality Of Service -->
                   <parameter>ONCE_AND_ONLY_ONCE</parameter>
                   <!-- Max Batch Size -->
                   <parameter>1</parameter>
                   <!-- Max Batch Time (-1 means infinite) -->
                   <parameter>-1</parameter>
                   <!-- Subscription name (no subscription name here)-->
                   <parameter><null /></parameter>
                   <!-- Client ID  (no client ID here)-->
                   <parameter><null /></parameter>
                   <!-- Add MessageID In Header -->
                   <parameter>true</parameter>
                   <!-- register the JMS Bridge in the AS MBeanServer -->
                   <parameter>
                       <inject bean="MBeanServer"/>
                   </parameter>
                   <parameter>org.hornetq:service=JMSBridge</parameter>
                 </constructor>
               <property name="transactionManager">
                   <inject bean="RealTransactionManager"/>
               </property>
           </bean>

           <!-- SourceCFF describes the ConnectionFactory used to connect to the
                source destination -->
           <bean name="SourceCFF"
                class="org.hornetq.api.jms.bridge.impl.JNDIConnectionFactoryFactory">
               <constructor>
                   <parameter>
                       <inject bean="JNDI" />
                   </parameter>
                   <parameter>/ConnectionFactory</parameter>
               </constructor>
           </bean>

           <!-- TargetCFF describes the ConnectionFactory used to connect to the
            target destination -->
           <bean name="TargetCFF"
                class="org.hornetq.api.jms.bridge.impl.JNDIConnectionFactoryFactory">
               <constructor>
                   <parameter>
                       <inject bean="JNDI" />
                   </parameter>
                   <parameter>/ConnectionFactory</parameter>
               </constructor>
           </bean>

           <!-- SourceDestinationFactory describes the Destination used as the source -->
           <bean name="SourceDestinationFactory"
                class="org.hornetq.api.jms.bridge.impl.JNDIDestinationFactory">
               <constructor>
                   <parameter>
                       <inject bean="JNDI" />
                   </parameter>
                   <parameter>/queue/source</parameter>
               </constructor>
           </bean>

           <!-- TargetDestinationFactory describes the Destination used as the target -->
           <bean name="TargetDestinationFactory"
                class="org.hornetq.api.jms.bridge.impl.JNDIDestinationFactory">
               <constructor>
                   <parameter>
                       <inject bean="JNDI" />
                   </parameter>
                   <parameter>/queue/target</parameter>
               </constructor>
           </bean>

           <!-- JNDI is a Hashtable containing the JNDI properties required -->
           <!-- to connect to the sources and targets JMS resrouces         -->
          <bean name="JNDI" class="java.util.Hashtable">
             <constructor class="java.util.Map">
                <map class="java.util.Hashtable" keyClass="String"
                                                 valueClass="String">
                   <entry>
                      <key>java.naming.factory.initial</key>
                      <value>org.jnp.interfaces.NamingContextFactory</value>
                   </entry>
                   <entry>
                      <key>java.naming.provider.url</key>
                      <value>jnp://localhost:1099</value>
                   </entry>
                   <entry>
                      <key>java.naming.factory.url.pkgs</key>
                      <value>org.jboss.naming:org.jnp.interfaces"</value>
                   </entry>
                   <entry>
                      <key>jnp.timeout</key>
                      <value>5000</value>
                   </entry>
                   <entry>
                      <key>jnp.sotimeout</key>
                      <value>5000</value>
                   </entry>
                </map>
             </constructor>
          </bean>

          <bean name="MBeanServer" class="javax.management.MBeanServer">
             <constructor factoryClass="org.jboss.mx.util.MBeanServerLocator"
                          factoryMethod="locateJBoss"/>
          </bean>
    </deployment>

## 33.1. JMS Bridge Parameters

The main bean deployed is the `JMSBridge` bean. The bean is configurable by the parameters passed to its constructor.

## Note

To let a parameter be unspecified (for example, if the authentication is anonymous or no message selector is provided), use `<null />` for the unspecified parameter value.

- 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

- 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 Section 33.4, “Quality Of Service” for a 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 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 `HORNETQ_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 or JBoss AS MBeanServer)

- ObjectName

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

## 33.2. 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 HornetQ 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.hornetq.jms.bridge.ConnectionFactoryFactory`.

## 33.3. 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 HornetQ that looks up the destination using JNDI.

A new implementation can be provided by implementing `org.hornetq.jms.bridge.DestinationFactory` interface.

## 33.4. Quality Of Service

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

### 33.4.1. 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.

### 33.4.2. 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.

### 33.4.3. 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 HornetQ 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 JBoss Transactions JTA * implementation which is a fully recovering transaction manager, thus providing a very high degree of durability. If JTA is required then both supplied connection factories need to be XAConnectionFactory implementations. This is likely to be the slowest mode since it requires extra persistence for the transaction logging.

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.

### 33.4.4. 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.

However since a third party JNDI is used, in this case the JBoss naming server, it is possible for the JNDI lookup to hang if the network were to disappear during the JNDI lookup. To stop this occuring the JNDI definition can be configured to time out if this occurs. To do this set the `jnp.timeout` and the `jnp.sotimeout` on the Initial Context definition. The first sets the connection timeout for the initial connection and the second the read timeout for the socket.

## Note

Once the initial JNDI connection has succeeded all calls are made using RMI. If you want to control the timeouts for the RMI connections then this can be done via system properties. JBoss uses Sun's RMI and the properties can be found here. The default connection timeout is 10 seconds and the default read timeout is 18 seconds.

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

### 33.4.5. Examples

Please see Section 11.3.5, “JMS Bridge” which shows how to configure and use a JMS Bridge with JBoss AS to send messages to the source destination and consume them from the target destination.

Please see Section 11.1.27, “JMS Bridge” which shows how to configure and use a JMS Bridge between two standalone HornetQ servers.

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