Memory leak with Spring integration test context caching

I’ve recently had to debug another out of memory with our Spring integration tests. The tests are configured to create a heapdump on out of memory so I loaded it up with the Eclipse Memory Analyser and this is what I saw:

This shows that there are six instances of the Hibernate session factory, taking 200Mb each. For our tests, there should be two. Spring caches the test context, and we have two different contexts, so there should be once instance of each. The above output suggests new contexts were being created for some tests, but why? I looked through the log output and then opened the tests that caused a new Spring context to be created, and discovered they were configured like this:

@ContextConfiguration(locations = {"classpath:main-test-context.xml", "classpath:another-test-context.xml"})
@Rollback
@Test(groups = "integration")
public class SomeIntegrationTest {

This test uses the main test context, but adds some more beans from a second context file. The problem is that because it is using a single @ContextConfiguration annotation, this is treated as a new context, so the entire thing is created from scratch. To achieve reuse of the existing context, you need to define a context hierarchy, like this:

@ContextHierarchy({
    @ContextConfiguration("classpath:main-test-context.xml"), 
    @ContextConfiguration"classpath:another-test-context.xml")
})
@Rollback
@Test(groups = "integration")
public class SomeIntegrationTest {

Note that this is different however – you are no longer getting a context which is merge of the two sets of beans, but rather a parent and child context. The consquences being:

1. If you have a Spring property bean in the parent context, beans in the child context will not get injected with those properties. You will need to add another property bean in the child context and point it at the relevant property files.
2. If you override beans in the child context and they are intended to be injected into beans defined in the parent context, this will no longer work. I fixed this by updating the relevant tests to manually set the overridden beans into the relevant classes in an @BeforeClass method, then reset them back in an @AfterClass method.

We also had one test defined using a wildcard asterisk in the context name, like this:

@ContextConfiguration(locations = {"classpath*:main-test-context.xml"})
@Rollback
@Test(groups = "integration")
public class SomeIntegrationTest {

This was also treated as a new context!

After making these changes, I was able to verify that only two session factories were created, so the contexts were being retrieved from the cache correctly.