The Spring Framework is a powerful and flexible framework that has become a staple in the Java ecosystem, primarily due to its focus on creating loosely coupled, robust applications. This post will walk you through the core aspects of Spring, including dependency injection, inversion of control, Spring modules, and more.

Spring is often called the “framework of frameworks.” Developed by Rod Johnson in 2003, it helps Java developers create applications that are flexible and modular by promoting dependency injection (DI) and inversion of control (IoC). With Spring, developers can avoid tight coupling between different parts of an application, making it easier to maintain and scale over time.

1. Spring Core
   At the heart of Spring lies the Core module, which supports dependency injection (DI) and inversion of control (IoC). Through these patterns, Spring manages the creation and interaction of objects, minimizing dependencies.
2. Spring Data Integration
   Spring Data modules include Spring JDBC and Spring ORM. These modules simplify database access and provide integration with ORM tools like Hibernate, allowing developers to interact with databases more easily.
3. Spring Web
   This module encompasses Spring MVC for web applications, REST APIs for building stateless web services, and Spring Boot for rapid setup. With Spring Web, developers can focus on building web applications without dealing with extensive configuration.
4. AOP (Aspect-Oriented Programming)
   Spring’s AOP support allows developers to manage cross-cutting concerns like logging and transaction management more effectively by separating them from the main application logic.

Before diving into Spring, it’s helpful to have a foundation in:

• Java Core Concepts: OOP, classes, methods, overloading, and overriding
• JDBC: Understanding Java Database Connectivity
• Hibernate: Basic ORM knowledge
• Servlet and JSP: Basics of building web applications in Java

Dependency Injection (DI) and Inversion of control (IoC)

Dependency Injection is a design pattern that makes applications loosely coupled by injecting dependencies rather than hardcoding them. This is where Spring’s IoC container steps in, managing object creation and dependency injection at runtime.

public class Students {
    private int student_id;
    private Marks marks;
    public Students() {
    }
}

public class Marks {
 private int marks_id;
 private String subject_name;
 public Marks() {
 }
}

For Instance:
In the above example, Class Students depends on Class Marks, making them tightly coupled. Using Spring, however, Class Marks is instantiated by the framework and injected into Class Students, achieving loose coupling.

IoC Container in Spring

The IoC container in Spring is responsible for:

• Creating objects
• Managing the lifecycle of objects
• Injecting dependencies

To configure these dependencies, we use either XML configuration files or annotations.

The Spring Framework consists of a wide range of modules, each targeting different areas of application development. These modules can be used independently or together to build flexible, maintainable, and scalable applications. The key modules are detailed in the next section.

You can explore each module in more detail by clicking on the link provided.