Beans

• Bean is an object and is managed by the Spring IoC container.
• It also forms the backbone of your application.
• Spring IoC container instantiates, assembles, and otherwise manages bean.
• Creation of beans is done with the help of configuration metadata that we supply to the container.
• Bean Scopes –
  1. singleton
     • This limits the scope of a bean definition to a single instance per Spring IoC container (default).
  2. prototype 
     • This limits the scope of a single bean definition to have any number of object instances.
  3. request 
     • This limits the scope of a bean definition to an HTTP request.
  4. session 
     • This limits the scope of a bean definition to an HTTP session.
  5. global-session 
     • This limits the scope of a bean definition to a global HTTP session.

Dependency Injection

• It is a technique whereby one object (or static method) supplies the dependencies of another object.
• It is a design pattern that helps us implement IoC.
• Dependency Injection is responsible for the creation of dependent objects outside of a class. It also provides those objects to a class in different ways.
• It helps to move the creation and binding of the dependent objects outside of the class that depends on them.
• Types of DI –
  1. Constructor-based
     • It is achieved when the class constructor is invoked by the spring container along with some arguments, where each argument is representing a dependency on the other class.
  2. Setter-based
     • It is achieved when after invoking a no-argument constructor or no-argument static factory method, then spring container calls the setter methods on the bean to instantiate the bean.

IOC Containers

• The Spring creates the objects, wire them together, configure them, and manage their complete life cycle from creation till destruction.
• The container gets its instructions with the help of the configuration metadata provided, about what objects to instantiate, configure, and assemble.
• It makes use of Java POJO classes and configuration metadata to produce a fully configured and executable system or application.
• Types of a container :
  1. BeanFactory
     • This container provides the basic support for DI and is defined by the org.springframework.beans.factory.BeanFactory interface.
  2. ApplicationContext
     • This container is defined by the org.springframework.context.ApplicationContext interface.
     • It adds more enterprise-specific functionality. For instance, it resolves textual messages from a properties file and publishes the application events to interested event listeners.