What Is a Spring Application Context?

Spring contexts are also called Spring IoC containers, which are responsible for instantiating,, and assembling beans by reading configuration Java annotations.

From: https://dzone.com/articles/what-is-a-spring-context

@Service
public class GreetingService {

    public void greet() {
        System.out.println("Welcomeon Spring!!!");
    }
}

@Service,at the class level, means that this is a service and is eligible to be registered as a bean in the Spring context.

How to register a class in the Spring Context?

By using annotation on the class:

• @Service
• @Component
• @Repository
• @Contoller
• @Bean

Spring Singleton

From: http://javabeat.net/spring-singleton-java-singleton/

The scope of the Spring singleton is best described as per container and per bean. If you define a bean for a particular class in a single container, spring container will create only one instance for the class.

Singleton scope is the default scope for spring beans.

What is a Spring bean?

The objects that form the backbone of your application and that are managed by the Spring IoC container are called beans.

A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container.

These beans are created with the configuration metadata that you supply to the container, for as annotations @Service, @Controller..etc

Spring Bean Scope

Please note, the only mostly used one is Singleton

• Singleton - (default) Only one instance of the bean is created in the IOC container

• Prototype - A new instance is created each time the bean is requested.

• Request - A single instance per http request. Only valid in the context of a web-aware Spring ApplicationContext.

• Session - A single instance per http session. Only valid in the context of a web-aware Spring ApplicationContext.

• Global-session - A single instance per global session. Typically Only used in a Portlet context. Only valid in the context of a web-aware Spring ApplicationContext.

• Application - bean is scoped to the lifecycle of a ServletContext. Only valid in the context of a web aware.

• Websocket - Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext.

• Custom Scope - Spring Scopes are extensible, and you can define your own scope by implementing Spring’s ‘Scope” interface