Memory growth when repeatedly loading ApplicationContext with @Transactional beans lacking interfaces

Answer

When a new ApplicationContext is created repeatedly in a test loop without closing it, each context keeps its own CGLIB proxy for every @Transactional bean that has no interface. The proxy holds a strong reference to the target bean, so the entire bean graph remains reachable until the context is destroyed. This is the source of the observable heap increase.

Confirmed facts (Spring 6.x, Java 17+)

• The default proxy strategy for a bean that lacks an interface is proxy-target-class=true (CGLIB subclassing).
• Setting proxy-target-class=false forces Spring to use JDK dynamic proxies. Those require at least one interface; otherwise a BeanCreationException is thrown and the context will not start.
• When the context is not closed, the BeanFactory retains the CGLIB proxy and the target instance, keeping them reachable and preventing GC.
• Closing the context (or using a try‑with‑resources block) releases all references, and heap usage stabilises across iterations.

Practical steps to avoid the leak

1. Always close the context after each iteration:

   try (AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class)) {
       // use ctx
   }
   

2. Or add an interface to the bean: the bean can still use the default CGLIB strategy, but the proxy will be a JDK proxy if proxy-target-class=false and an interface is present. The leak is still prevented by closing the context.
3. If you must keep a long‑lived context: refactor transactional logic into a component that implements an interface, or move the @Transactional annotation to a separate service that does have an interface.

Verification checklist

• Is the ApplicationContext closed after each loop iteration?
• If proxy-target-class=false is used, does the bean implement at least one interface?

Answering these questions will tell you whether the heap increase is due to the proxy strategy or simply the context lifecycle.