bmt (Bean Managed Transactions): Stepping Outside the Container (with JPA and JTA)
Author: Mike Musgrove
What is it?
On occasion the application developer requires finer grained control over the lifecycle of JTA transactions and JPA Entity Managers than the defaults provided by the JEE container. This example shows how the developer can override these defaults and take control of aspects of the lifecycle of JPA and transactions.
[But note that a JEE container is designed with robustness in mind so you should carefully analyse the scaleabiltiy, concurrency and performance needs of you application before taking advantage of these techniques in your own applications.]
The example demonstrates how to manually manage transaction demarcation whilst accessing JPA entities in JBoss AS 7:
- part 1 shows the developer responsibilities when injecting an Entity Manager into a managed (stateless) bean.
- part 2 shows the developer responsibilities when using JPA and transactions with an unmanaged component
All you need to build this project is Java 6.0 (Java SDK 1.6) or better, Maven 3.0 or better.
The application this project produces is designed to be run on a JBoss AS 7 or JBoss Enterprise Application Platform 6. The following instructions target JBoss AS 7, but they also apply to JBoss Enterprise Application Platform 6.
Deploying the application
First you need to start JBoss AS 7 (or JBoss Enterprise Application Platform 6). To do this, run
or if you are using windows
To deploy the application, you first need to produce the archive to deploy using the following Maven goal:
You can now deploy the artifact to JBoss AS by executing the following command:
This will deploy
target/jboss-as-bmt.war to the running instance of the AS.
The application will be running at the following URL http://localhost:8080/jboss-as-bmt/BMT.
To undeploy from JBoss AS, run this command:
If you need to redeploy the war then ensure that you explicitly undeploy it first so that databases are cleaned up correctly.
You can also start JBoss AS 7 and deploy the project using Eclipse. See the Getting Started Developing Applications Guide for more information.
Using the application
JBoss AS 7 comes with an H2 datasource by default. The example shows how to transactionally insert key value pairs into to this H2 database and demonstrates the requirements on the developer with respect to the JPA Entity Manager.
To access the application type the following into a browser:
You will be presented with a simple form for adding key value pairs and a checkbox to indicate whether the updates should be executed using an unmanaged component (effectively this will run the transaction and JPA updates in the servlet - ie not session beans). If the box is checked then the updates will be executed within a session bean method.
To list all pairs leave the key input box empty. To add or update the value of a key fill in the key and value input boxes. Press the submit button to see the results.
Downloading the sources and Javadocs
If you want to be able to debug into the source code or look at the Javadocs of any library in the project, you can run either of the following two commands to pull them into your local repository. The IDE should then detect them.
mvn dependency:sources mvn dependency:resolve -Dclassifier=javadoc