If you are looking for an embeddable EJB3 Container for your unit-tests/integration-tests,
OpenEJB is currently the most mature solution (alternatives are
embedded Glassfish and
JBoss embedded).
The
documentation and the
samples of OpenEJB are really neat and enable an easy jump-start. All the examples are automated tests that run with a simple
mvn clean install.
After a while however I came across the following problem: The embedded container is not restarted by default between tests. If you have two tests (even in several test classes), each starting the embedded container, then the second test gets passed the same instance of the embedded container as the first one.
This has the potential for shared state between the tests and strange side-effects as a consequence.
The first occurrence is when you are accessing an (sandboxed) database, that gets initialized (hibernate create-drop) when initializing the persistence-unit. Since the container is not restarted for the second test, the persistence-unit does not get initialized a second time. This means you have all the traces from your first test in the database...
An easy way to work around this, is the
undocumented feature of OpenEJB to destroy the container when closing the initial context.
This is achieved by setting the property "
openejb.embedded.initialcontext.close" to "
destroy" on the InitialContext.
Now my test harness looks like this:
@Before
public void setUp() throws Exception{
Properties p = new Properties();
//Set some other properties like datasources ...
p.put("openejb.embedded.initialcontext.close", "destroy");
context = new InitialContext(p);
}
@After
public void tearDown() throws Exception{
context.close();
}
It should be kept in mind, that restarting the embedded container can have implications on the performance.
In my first tests on my MacBook, the repeated startup of the container takes about 200 ms, which I find acceptable for integration tests... but probably the concrete deployment scenario has an influence on the startup time ...
I like the following quote from Jay Field's screencast The 5 Ws of DSLs:
Thanks 
Abstraction is a central concept in software development.
Recently I have become a 
Old-school heavyweight concepts from the ages of EJB2 still tantalize a lot of the Java enterprise projects.
