What is Spring?

• Spring Framework: A powerful, lightweight framework for building Java applications. It simplifies the development of enterprise-grade applications through support for various infrastructural concerns (e.g., transaction management, security, etc.).

Why is Spring Useful?

• Simplified Dependency Management: Manages libraries and dependencies in your project efficiently, reducing conflicts and compatibility issues.
• Promotes Good Practices: Encourages developers to follow best practices and design patterns, such as Dependency Injection (DI) and Aspect-Oriented Programming (AOP).
• Versatility: Supports a wide range of applications, from small stand-alone applications to large, complex enterprise systems.

Dependency Injection (DI)

Dependency Injection is a design pattern used to implement IoC (Inversion of Control), where the control over the dependencies of a class shifts from the class itself to a framework or container. In simpler terms, DI allows classes to be more loosely coupled, making them more modular, easier to test, and maintain.

How DI Works:

• Without DI: Typically, an object creates its own dependencies, leading to tight coupling between the components. Changing a dependency might require changes to the dependent class.
• With DI: Dependencies are "injected" into an object at runtime, rather than being hard-coded within the object. This can be done through constructors, setters, or properties.

Benefits of DI:

• Decoupling: Classes do not need to know about the creation and configuration of their dependencies, leading to a decoupled architecture.
• Testability: Easier to test classes by injecting mock dependencies, facilitating unit testing and behaviour testing without requiring the actual dependencies.
• Flexibility and Reusability: Components can be easily replaced or reused in different contexts since they are not tightly coupled to their dependencies.

Aspect-Oriented Programming (AOP)

Aspect-Oriented Programming is a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns. It does so by adding additional behaviour to existing code (an advice) without modifying the code itself.

Key Concepts:

• Aspect: A module that encapsulates behaviours that affect multiple classes into reusable modules. It's the AOP equivalent of a class in OOP.
• Join Point: A point during the execution of a program, such as the execution of a method or the handling of an exception.
• Advice: Action taken by an aspect at a particular join point. Different types of advice include "before," "after," and "around" that define when the code should be executed in relation to the join point.
• Pointcut: A predicate that matches join points. Advises are associated with a pointcut expression and run at any join point matched by the pointcut (for example, execution of methods with a certain annotation).
• Target Object: Object being advised by one or more aspects. It's often a proxy object in the Spring Framework, allowing it to weave in advice with the target object's method calls.

Benefits of AOP:

• Separation of Concerns: By separating cross-cutting concerns (like logging, transaction management, or security) from the business logic, the code becomes cleaner and more maintainable.
• Reduced Code Duplication: Common functionalities that are spread across multiple classes can be centralised in aspects, reducing code duplication.
• Improved Code Modularity: AOP makes it easier to add or change cross-cutting concerns without touching the core business logic, leading to more modular and adaptable code.

What is Spring Boot?

• Spring Boot: An extension of the Spring framework that simplifies the initial setup and development of new Spring applications. It offers a way to create stand-alone, production-grade Spring based applications easily.

Why is Spring Boot Useful?

• Simplified Dependency Management: Automates and manages dependencies effectively with the concept of starters (e.g., spring-boot-starter-web for web applications), making dependency management manageable.
• Simplified Deployment: Simplifies the deployment process by creating self-contained applications that don't require an external servlet container.
• Autoconfiguration: Automatically configures your application based on the libraries you have added, making it easier to get a project up and running quickly.

Three Core Features of Spring Boot

1. Simplified Dependency Management:
2. Uses a set of "Starters" (e.g., spring-boot-starter-web) to bundle common dependencies together, simplifying the build configuration.
3. Leverages Bill of Materials (BOMs) to ensure that all dependencies work well together without version conflicts.
4. Simplified Deployment:
5. Creates self-contained applications that can be run as standalone Java applications, simplifying the deployment process.
6. Removes the need for external application servers by embedding servers like Tomcat, Jetty, or Undertow directly.
7. Autoconfiguration:
8. Automatically configures your Spring application based on the jar dependencies you added. For example, if spring-boot-starter-web is in your class path, Spring Boot auto-configures a web application.
9. Described as "magic" by newcomers, it significantly reduces the need for manual configuration and boilerplate code.

Dependency Management Challenges

• Dependency Conflicts: Using multiple libraries together can lead to version conflicts, where one library's update breaks another.
• Complexity: Managing dependencies and ensuring compatibility across different environments can be complex and time-consuming.

Bill of Materials (BOMs)

• A BOM is a special kind of POM (Project Object Model) in Maven that defines a list of dependencies and their versions that are known to work well together.
• Spring Boot uses BOMs to control the versions of dependencies, making it easier to manage them without specifying versions explicitly.

Spring Boot Starter Web

• A starter that provides all the necessary dependencies to build a web application. This includes embedded servers, Spring MVC, and more, bundled in a single dependency.

Application Servers and Spring Boot

• Before Spring Boot: Deploying Java applications involved installing and configuring an application server, managing database drivers, creating database connections, and more.
• With Spring Boot: These steps are simplified or automated, making the development and deployment process much smoother.

Shading & Nesting Jars

• Shading: The process of creating a uber-jar (or fat jar) that contains all of your application's dependencies packaged together. This helps in avoiding conflicts with other jars by renaming packages.
• Nesting Jars: Spring Boot supports nesting jars (jars within a jar), which is part of how it creates executable jars. This makes deployment easier by packaging everything needed to run the application into a single executable jar.

Autoconfiguration: The "Magic"

• Spring Boot's autoconfiguration automatically sets up your application based on the dependencies you have added, reducing the need for explicit configuration and making it easier for beginners to start projects.