在JUnit中加载Spring bean时出现OutOfMemory错误

Question

I am in the process of switching an application to use spring and dynamically load some classes at runtime. This change is leading to consistent 'java.lang.OutOfMemory: PermGen Space' errors when running our JUnit-based test suite through maven. We have about 800 tests, and the OoM is thrown about 200 tests in. The code changes are as follows:

private Obj buildMyObj() {
    //Obj obj = MyObj(1); //Old method to get obj
    ObjInterface obj = (ObjInterface) MyAppContext.INSTANCE.getApplicationContenxt().getBean("Obj");
}

And in the xml file, I have added the following:

<bean id="Obj" class="com.project.obj.ObjImplOne">
    <constructor-arg name="arg0" val="1"/>
</bean>

The buildMyObj() method is being run approximately once per unit test, though some will call it many times. The previous method, declaring the object directly (before we moved to the interface approach) worked fine. However, now that we've got an interface and may use several different implementations at runtime, we need to load it at runtime and JUnit isn't playing along.

I've followed up on some of the existing stackoverflow threads, and it appears that whenever Spring loads a class dynamically, it puts it in the PermGen, but isn't smart enough to identify a subsequent load of the class as identical and leads to every call placing a new class in the PermGen, hence the error. It was suggested to allow Class Unloading with the '-XX:+CMSClassUnloadingEnabled' JVM option (the suggestion was '-XX:+CMSClassUnloadingEnabled -XX:+CMSPermGenSweepingEnabled', but the JVM complained with "Please use CMSClassUnloadingEnabled in place of CMSPermGenSweepingEnabled in the future"

But that hasn't changed anything, the error is still being thrown.

EDIT: After watching the test suite run and monitoring top in a separate terminal, it doesn't appear the JVM is doing anything to reclaim the classes which are being loaded. I uppoed the permgen size per a suggested comment, and java simply continued claiming memory for a longer time (over 2 gigs worth). Is there an issue with Class Loading and getBean()?

Answer 1

The solution was to properly scope the bean when declaring it in the xml file: Spring defaults to singleton, which I'm guessing is why a new one was created with every call to buildMyObj(). Setting the scope to prototype fixed my memory issues completely:

<bean id="Obj" class="com.project.obj.ObjImplOne" scope="prototype">
    <constructor-arg name="arg0" val="1"/>
</bean>