z2-Environment

h1. Using Z2 with a Transaction Manager

This sample demonstrates how to use Z2 with the Atomikos transaction manager. There is another sample that shows how to use Z2 with a Spring configured transaction manager. See [[sample-jta-spring]]. In contrast to that, this sample is less sophisticated but probably better suited to understand the underlying mechanics.

The Wiki page [[How_to_TransactionManager]] explains the general principles behind transaction handling in Z2.

This sample is stored in "z2-samples.jta-plain":http://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain. It implements exactly the same scenario as [[Sample-hibernate-basic]] with the exception of not using the built-in JTA implementation.

h2. Prerequisites

{{include(Java Version Requirements)}}

You need to run Java DB as network server on localhost. This is explained next.

The application will create a database "z2-samples"

{{include(How to run Java db)}}

h2. Running the sample

{{include(Install_sample_prefix)}}

Check out the sample

<pre><code class="ruby">

git clone -b v2.6 http://git.z2-environment.net/z2-samples.jta-plain

</code></pre>

{{include(Install_sample_postfix)}}

h2. Verifying

When everything is up, go to http://localhost:8080/jta-plain. You see something like this: 

!plain_thingies.png!

And indeed, the implemented function is rather obvious: Manage a table of strings - called Thingies in the sample.

h2. Now to the point...

The idea behind this sample is to provide a template for transaction manager integration. Note that before you integrate with a complete transaction management system, you should be sure that you need it. Distributed transactions come at a price in terms of complexity and overhead of local transaction logs. If you do not have multiple data sources, or if those have no strong inherent consistency requirement you may well be better off without a full-blown, XA capable transaction manager. Please also see [[How to transaction management]].

h2. Detailed explanation

The sample has four modules:

* *com.atomikos*: This module holds the "Atomikos Transaction Essentials":http://www.atomikos.com/Main/TransactionsEssentials libraries - the actual transaction manager implementation (via the mvn fragment "mvnFragment":https://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain/revisions/master/ee ntry/com.atomikos/mvnFragment.properties).

* *com.zfabrik.samples.jta-plain*: This module implements supporting functions for the actual applications.

* *com.zfabrik.samples.jta-plain.domain*: The domain definition module. This contains the JPA entities and a "Thingy Repository" implementation.

* *com.zfabrik.samples.jta-plain.web*: The simple web application that lists the database content and allows to add and delete thingies.

In order to make Atomikos usable, it's transaction manager and user transaction implementations have to be configured and instantiated. All of that is done in *com.zfabrik.samples.jta-plain* in the form of Z2 components exposed for re-use by other modules. Similarly the Atomikos XA Data Source implementation is made available from this module (Note: You cannot -for all practical matters - separate data source implementations from the transaction management implementations).

Unlike [[Sample-jta-spring]], the starting point for integrations with the transaction management system - although done only once - are a little more _distributed_:

In order to simplify transaction manager access from various places, we use a utility class "Transactions":https://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain/revisions/master/entry/environment/java/src.api/com/zfabrik/samples/jta_plain/jta/Transactions.java. This class uses components in *com.zfabrik.samples.jta-plain* and effectively de-couples the JTA implementation from its access points. This class is used for

* *Jetty Web Container integration:* 

In order to provide user transaction access via the standard JNDI name @java:comp/UserTransaction@ (although not strictly needed in the example), we adapted "jetty.xml":https://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain/revisions/master/entry/environment/webServer/jetty.xml accordingly. Check the lines starting with

<pre><code class="xml">

<New id="tx" class="org.eclipse.jetty.plus.jndi.Transaction">...

</code></pre>

* *Hibernate integration:* 

Hibernate accesses the transaction manager via our custom "AtomikosJTAPlatform":https://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain/revisions/master/entry/com.zfabrik.samples.jta-plain/java/src.api/com/zfabrik/samples/jta_plain/hibernate/AtomikosJTAPlatform.java (see also http://stackoverflow.com/questions/20681245/how-to-use-atomikos-transaction-essentials-with-hibernate-4-3) as declared in the "persistence unit":https://redmine.z2-environment.net/projects/z2-samples/repository/z2-samples-jta-plain/revisions/master/entry/com.zfabrik.samples.jta-plain.domain/java/src.impl/META-INF/persistence.xml