What is IOC and DI?

It is a process whereas objects define their dependencies. Hare spring container responsible to injects those dependencies when it creates the bean. This process is fundamentally the inverse, hence the name Inversion of Control (IoC).

• The org.springframework.beans and org.springframework.context packages are the basis for Spring Framework's IoC container.
• The BeanFactory interface provides an advanced configuration mechanism capable of managing any type of object. ApplicationContext is a sub-interface of BeanFactory. It adds easier integration with Spring's AOP features; message resource handling (for use in internationalization), event publication; and application-layer specific contexts such as the WebApplicationContext for use in web applications.
• The interface org.springframework.context.ApplicationContext represents the Spring IoC container and is responsible for instantiating, configuring, and assembling the aforementioned beans.
• Your application classes are combined with configuration metadata so that after the ApplicationContext is created and initialized, you have a fully configured and executable system or application.  
•  Instantiating a Spring IoC container is straightforward. The location path or paths supplied to an ApplicationContext constructor are actually resource strings that allow the container to load configuration metadata from a variety of external resources such as the local file system, from the Java CLASSPATH, and so on.
  

  ApplicationContext context =
      new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});

  The ApplicationContext is the interface for an advanced factory capable of maintaining a registry of
  different beans and their dependencies. Using the method t.getBean(String name, Class<T> requiredType) you can
  retrieve instances of your beans.