dbsynch sample app


this sample demonstrates a spring , activemq and MySql application using XA(JTA) transactions.

the application is meant to copy a database table from one database to another using JMS as the transport.

there are three components:

    * server - this is the activemq broker, activemq is embedded in a spring context.

    * producer - this is a client to the broker, it reads rows from a database table,source_table, and for every row sends 	a JMS message to a queue called source-queue.

    * collector - this is a client that reads messages from source-queue and for every message creates a database row in a 	table called dest_table.


The stack used in the sample:

Spring as a container.
Activemq
MySql
Atomikos 





XA tansactions:
this sample shows two implementations to manage jms and jdbc resources in one transaction.

    * A non xa transaction where both resources are just committed one after the other in a way that if one of them fails 	it will not create a lot of damage, maybe a message will be processed twice.

    * JTA XA transactions using Atomikos, http://www.atomikos.com/Main/WebHome


see the spring files in producer and collector projects , nonxa-XX and atomikos-xa-XX.


things to remember with JTA:
the data base ,driver and data source must be XA enabled.
Performance is poor with XA.
Many data bases do not fully implement JTA.


build:
this is a maven project.
to build the project, from the top most directory,where the parent pom is, execute 'mvn clean install'


the projects are:

    * server - this is the server project mainly used to embed activemq in a spring context.activemq can also be run out of 		the box, but embedding it in a spring application will make it easier to add functionality, for example we can add 	  	beans that connect to the broker with VM transport ,more control on activemq properties.

    * server-runtime - creates a runtime directory for the server.

    * common - a project with common classes for the three components.

    * producer - this is the client that reads the source table and sends a JMS message for every row.

    * producer-runtime - creates a runtime directory for the producer.collector - this is the client that reads the 		messages with the source rows and inserts rows to the dest_table.

    * collector – the client that reads the jms queue and inserts rows to the DB

    * collector-runtime - creates the runtime directory for the collector.



IDE:

to load to intelij IDEA just do: file -> open project , and select the parent pom, idea will do the rest.

to load to eclipse execute 'mvn eclipse:eclipse' from the top directory and load the projects to eclipse.
or use m2eclipse plugin.




Unit tests:

Unit tests with xa will work only with a data base that supports xa, also, an activemq broker must run in order for the unit tests to run. To build without unit tests run maven with

-Dmaven.test.skip=true



PubSub
to demonstrait pubsub domain:

the server publishes a notification to notification.topic every some interval.
see:
/server/src/main/resources/spring/spring-config-notifier.xml

both the producer and collector subscribe to this topic and receive notifications.
see:
/collector/src/main/resources/spring/spring-config-notification.xml
/producer/src/main/resources/spring/spring-config-notification.xml

 the collector can also be a durable subscriber,set the property durable=true in
  collector.properties
  the client id for the collector durable subscription is passed in the
  collector.properties file. to run two instances change the client id for each execution.