spring.txt

spring is
a) a framework for java applications
b) an ecosystem of connected modules - eg MVC (web), JPA (DB interaction), Security, etc

the core of spring revolves around dependency injection
previously we had dependencies between our own classes - eg service is dependent
on a DAO class, and had to instantiate a DAO class at the start

The first that Spring changes, is that it can allow us to avoid this and let Spring
manage all of our dependencies on its own

1-
now that we've got spring set up.. we can let it manage some dependencies
in this case, our class here will scan its package (being currently the entire 'java' folder)
for classes that are marked as components
next, it will manage those classes as dependencies for us
objects that are managed by Spring are referred to as beans

spring has something called the Inversion of Control container that contains all of these beans
Inversion of Control - means that the developer no longer manages dependencies - instead Spring controls them

2-
advantages of beans
a) Spring will manage 'scope' for us
scope of a bean - scope that a single instance of an object exists in

default is a Singleton - a single object that is shared across the entire application
Prototype resembles more of a regular java object - a new one is created every time the bean is referenced

there are more scopes we'll talk about later (all of them have to do with interacting with the web)

3-
more annotations :
@Component - designates this class as a candidate for a bean (a component of our application)
@Bean - designates a constructor for the component
@Autowired - automatically grab the appropriate bean to be used for this class

if you're looking into spring examples, you're going to see that spring is used wildly differently than
the way i'm writing here -
a) there is xml configuration (old) and annotation configuration
b) there are different types of autowirings - we can inject dependencies in three different ways
    i) we can use constructor injection (my preferred way)
    ii) we can write a setter method and add autowired over it (setter injection)
    iii) we can write autowired over the field itself (field injection, not recommended)
c) stereotyped annotations - we can also replace the @Component annotation with @Service or @Repository, etc
    this doesn't really do anything (other than eg default to a specific scope), it's just to make classes
    easier for developers to read and interpret
    i'm going to be using only @Component to help you understand the relationship between the class definition
    and its bean