Random Questions

 WeakHashMap

WeakHashMap is an implementation of the Map interface. WeakHashMap is almost same as HashMap except in case of WeakHashMap, if object is specified as key doesn’t contain any references- it is eligible for garbage collection even though it is associated with WeakHashMap. i.e Garbage Collector dominates over WeakHashMap.

Private method in interface

After Java 9, we can have private method in interface.

Spring Propagation

While dealing with Spring managed transactions the developer is able to specify how the transactions should behave in terms of propagation. In other words the developer has the ability to decide how the business methods should be encapsulated in both logical or physical transactions. Methods from distinct Spring beans may be executed in the same transaction scope or actually being spanned across multiple nested transactions. This may lead to details like how does the inner transaction outcome result affects the outer transactions.

REQUIRED behavior

Spring REQUIRED behavior means that the same transaction will be used if there is an already opened transaction in the current bean method execution context. If there is no existing transaction the Spring container will create a new one. If multiple methods configured as REQUIRED behavior are called in a nested way they will be assigned distinct logical transactions but they will all share the same physical transaction. In short this means that if an inner method causes a transaction to rollback, the outer method will fail to commit and will also rollback the transaction. Let's see an example:


Note that the inner method throws a RuntimeException and is annotated with REQUIRED behavior. This means that it will use the same transaction as the outer bean, so the outer transaction will fail to commit and will also rollback.

Note: The only exceptions that set a transaction to rollback state by default are the unchecked exceptions (like RuntimeException). If you want checked exceptions to also set transactions to rollback you must configure them to do so, but this will not be covered in this tutorial.

Note 2: When using declarative transactions, ie by using only annotations, and calling methods from the same bean directly (self-invocation), the @Transactional annotation will be ignored by the container. If you want to enable transaction management in self-invocations you must configure the transactions using aspectj, but this will not be covered in this tutorial.

REQUIRES_NEW behavior

REQUIRES_NEW behavior means that a new physical transaction will always be created by the container. In other words the inner transaction may commit or rollback independently of the outer transaction, i.e. the outer transaction will not be affected by the inner transaction result: they will run in distinct physical transactions.










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