Creating Memory Leaks with Spring

I've spent the last few days looking at Confluence's memory footprint.

The biggest win so far (besides turning off all the caches ) has been in Spring.

Spring keeps track of dependencies between the beans it manages, so if you inject bean A into bean B, Spring will record the fact. Spring will call B.setA(A) of course, to perform the injection. Then it adds the name of B to the list of beans which depend on A, so that during shutdown it can remove B before A.

Confluence autowires beans using the DefaultListableBeanFactory.autowireBeanProperties() method. This assumes that the bean is a singleton, and registers it. It also doesn't check whether the bean it is registering is already a dependent of the bean being injected. So the linked list of dependencies grows with every page view. Five hundred views go it up to almost 10MB!

Spring does allow non-singleton beans, and it understands that they shouldn't be registered as dependents, but DefaultListableBeanFactory doesn't provide a way of autowiring a non-singleton bean.

I created a new factory to do the job:

private static class BucketListableBeanFactory extends DefaultListableBeanFactory
    {
        public BucketListableBeanFactory(ApplicationContext context)
        {
            super(context);
        }

        public void autowireNonSingletonBeanProperties(Object existingBean, int autowireMode, boolean dependencyCheck)
                throws BeansException
        {
            if (autowireMode != AUTOWIRE_BY_NAME && autowireMode != AUTOWIRE_BY_TYPE)
            {
                throw new IllegalArgumentException("Just constants AUTOWIRE_BY_NAME and AUTOWIRE_BY_TYPE allowed");
            }
            RootBeanDefinition bd = new RootBeanDefinition(existingBean.getClass(), autowireMode, dependencyCheck);
            bd.setSingleton(false);
            populateBean(existingBean.getClass().getName(), bd, new BeanWrapperImpl(existingBean));
        }
    }

That's just a copy of autowireBeanProperties(), with the addition of a call to setSingleton().

Confluence's calisthenics and orthodontia is under way. Soon we'll be running light without overbyte!