StackHolder - Jakub Kubrynski

I can bet that every Java developer at least heard about L1 (aka EntityManager or Session) cache. But is your level of understanding it good enough? If you're not sure, consider going through this post. At first, we need to know what the persistence context is. Following EntityManager JavaDoc  we know, that: "A persistence context is a set of entity instances in which for any persistent entity identity there is a unique entity instance. Within the persistence context, the entity instances and their lifecycle are managed."  In fact, the first level cache is the same as the  persistence context . That means operations such as persist() , merge() , remove()  are changing only internal collections in the context and are not synchronized to the underlying database. What is the mosts important here is what happens when you invoke the  clear()  method. It clears the L1 cache. But we know L1 == persistence context. Does it mean clearing L1 removes al...

Caching solves wide sort of performance problems. There are many ways to integrate caching into our applications. For example when we use Spring there is easy to use @Cacheable support. Quite easy but we still have to configure cache manager, cache regions, etc. Sometimes it's unfortunately like taking a sledgehammer to crack a nut. So what can we do to "go lighter"? There is a technique called  memoization . Technically it's as easy as pie but true genius lies in simplicity. Model solution looks as follows: public Foo getValue() { if (storedValue == null) { storedValue = retrieveFoo(); } return storedValue; } As you can see there is no problem in implementing it manually, but as long as we remember about DRY rule we can use already implemented solutions which additionally provides thread safety. Pretty good idea is to use  Guava  library. // create Supplier<Foo> memoizer = Suppliers.memoize(this::retrieveFoo); // and use Foo variable = mem...