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.
- With the help of configuration metadata that we supply to the container, beans are created.
- Bean Scopes –
- singleton – This limits the scope of a bean definition to a single instance per Spring IoC container (default).
- prototype – This limits the scope of a single bean definition to have any number of object instances.
- request – This limits the scope of a bean definition to an HTTP request.
- session – This limits the scope of a bean definition to an HTTP session.
- 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 used to 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 –
- 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.
- 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 –
- BeanFactory – This container provides the basic support for DI and is defined by the org.springframework.beans.factory.BeanFactory interface.
- 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.