What is Dependency Injection in Spring?

Dependency injection in Spring is a design pattern that allows the implementation of Inversion of Control (IoC) principle by providing components with their dependencies rather than having the components create or manage their dependencies. This helps in decoupling the components and making the system more modular, testable, and maintainable.

How is Dependency Injection Achieved in Spring?

In Spring, dependency injection is achieved through the use of BeanFactory or ApplicationContext containers. These containers manage the creation and configuration of objects and their dependencies. There are three ways to perform dependency injection in Spring:

1. Constructor Injection: Dependencies are provided through the component's constructor.
2. Setter Injection: Dependencies are set using setter methods.
3. Field Injection: Dependencies are directly injected into fields using annotations like @Autowired.

By utilizing dependency injection in Spring, developers can easily manage and inject dependencies, leading to more flexible and maintainable code.