The Spring container is at the core of the Spring Framework. The container will create the objects, wire them together, configure them, and manage their complete life cycle from creation till destruction. The Spring container uses DI to manage the components that make up an application. These objects are called Spring Beans.

The container gets its instructions on what objects to instantiate, configure, and assemble by reading the configuration metadata provided.

The configuration metadata can be represented either by XML, Java annotations, or Java code. The following diagram represents a high-level view of how Spring works.

Spring Container Flow
Spring Container Flow

The Spring IoC container makes use of Java POJO classes and configuration metadata to produce a fully configured and executable system or application.

The main tasks performed by IoC container are:

  1. Instantiate the application class
  2. Configure the object
  3. Assemble the dependencies between the objects

There are two types of IoC containers. They are:

  1. BeanFactory
  2. ApplicationContext

Using BeanFactory

The XmlBeanFactory is the implementation class for the BeanFactory interface. To use the BeanFactory, we need to create the instance of XmlBeanFactory class as given below:

The constructor of XmlBeanFactory class receives the Resource object so we need to pass the resource object to create the object of BeanFactory.

Using ApplicationContext

The ClassPathXmlApplicationContext class is the implementation class of ApplicationContext interface. We need to instantiate the ClassPathXmlApplicationContext class to use the ApplicationContext as given below:

The constructor of ClassPathXmlApplicationContext class receives string, so we can pass the name of the xml file to create the instance of ApplicationContext.

Difference between BeanFactory and the ApplicationContext

The org.springframework.beans.factory.BeanFactory and the org.springframework.context.ApplicationContext interfaces acts as the IoC container. The ApplicationContext interface is built on top of the BeanFactory interface.

It adds some extra functionality than BeanFactory such as simple integration with Spring’s AOP, message resource handling (for I18N), event propagation, application layer specific context (e.g. WebApplicationContext) for web application. So it is better to use ApplicationContext than BeanFactory.

Reference Docs:
Spring IoC Containers Reference
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