Spring core container is the basis for complete Spring framework?

All websites state that the Spring core container is the basis for complete Spring framework i.e., it is used across the all modules like AOP, JDBC module, Web module, etc. As per my understanding, the Spring core container's main purpose is to inject dependencies, so avoiding the need of factory classes and methods. Is that correct?

Second question: When it is said, Spring core container is the basis for complete Spring framework (e.g., for Spring AOP). As per my understanding, in Spring AOP also,开发者_运维技巧 getting the object of classes like ProxyFactoryBean is achieved by core container. Right?

Thirdly, it is stated that Spring core container avoids the need for programming the use of singletons. How come singleton classes are avoided by core container?

---

1. yep

2. yep

3. All beans declared in Spring config files are singleton by default. They are instantiated when your application starts.

---

First off, your understanding of what you get from Spring is about right. So let's get on to your third question, the interesting one.

The key is it's not that you don't have singletons, it's that they're singletons by configuration. This is a vital difference, as it means you can avoid all the complicated singleton enforcement code (the source of frequent problems) and instead just write exceptionally simple programs that focus on the business end of things. This is particularly important when you are writing a program with non-trivial object lifetimes: for example, in a webapp it makes it very easy to manage the lifespan of objects that hold state associated with a user's session, since if the objects have session scope, they'll be “singleton per user session”. That's enormously easier to work with than many of the alternatives.

The fact that Spring can also help out with transactions is just perfect as transaction handling is distinctly non-trivial, and AOP is the best solution to them in Java that I've seen (other languages have other options open) with Spring supporting a pretty straight-forward way of doing it. Try to do it properly without if you don't believe me. Spring's pretty much wonderful.