Intro to Springboot, Dependency, Injection, Ioc, Mvc

Topics to be Covered:¶

Project Overview:
- Understand the structure and features of the Basic Ecommerce Platform.
- Discuss the end-to-end development process, covering essential ecommerce functionalities like user authentication, payment processing, and product search.
Frameworks in Software Development:
- Introduction to what frameworks are and why they are critical in modern software engineering.
- A comparison of various frameworks across different programming languages, emphasizing their role in simplifying common tasks.
Why Choose Spring?
- A deep dive into the Spring Framework, highlighting its benefits, including Dependency Inversion, Dependency Injection, and Inversion of Control (IoC).
- Explanation of why Spring is the de facto standard for enterprise-grade Java applications.
Model-View-Controller (MVC) Architecture:
- Introduction to the MVC design pattern, its components, and how it structures web applications for maintainability and scalability.
Spring Boot Application:
- Hands-on creation of a Spring Boot application, demonstrating the ease of setup and development using Spring Boot.

What Project Will We Be Building?¶

Project Overview:¶

Objective:
- The main goal of this Article is to teach you how to build an Basic Ecommerce Platform from scratch, mirroring a simplified version of platforms like Flipkart or Amazon.
- The project will not only teach you the technical aspects of building an ecommerce site but also expose you to real-world challenges and best practices in software development.
Scope of the Project:
- By the end of the Arcticle, you will have a fully functional ecommerce platform. The platform will include critical features such as:
  - Authentication: Implementing user login, registration, and session management.
  - Payment Processing: Integrating payment gateways to handle transactions securely.
  - Recommendation Engine: Using algorithms to suggest products based on user behavior and preferences.
  - Product Details: Displaying detailed information about products, including images, descriptions, and prices.
  - Search Functionality: Allowing users to search for products efficiently, using features like auto-complete and filtering.
Reference Material:
- Review the Product Requirements Document (PRD), which outlines the functional and non-functional requirements for the ecommerce platform. This document serves as a blueprint for what the final product should achieve.

Tools Required:¶

Postman:
- A tool for testing APIs. You'll use it extensively to test the various endpoints of your ecommerce platform as you build them.
IntelliJ IDEA Ultimate:
- The integrated development environment (IDE) we'll be using for writing and testing Java code. It provides robust features like smart code completion, refactoring, and debugging.
- GitHub Student Pack:
  - Ensure you activate the GitHub Student Developer Pack, which offers a free 1-year license for IntelliJ IDEA Ultimate. This license will provide access to all the advanced features of the IDE, which are crucial for efficient development.

What Are Frameworks and Why Do We Need Them?¶

Frequent Tasks in Software Engineering:¶

In any software development project, certain tasks are almost always necessary, regardless of the specific problem you're solving. These tasks include:
- Developing APIs:
  - APIs (Application Programming Interfaces) allow different parts of your system to communicate with each other, and also enable external systems to interact with your application.
- Interacting with Databases:
  - Cache Systems: Tools like Redis or Memcached are used to store frequently accessed data in memory, reducing the load on the database and improving application performance.
  - NoSQL Databases: Non-relational databases like Elasticsearch and MongoDB provide flexible data storage solutions that can handle large volumes of unstructured data.
  - Messaging Queues: Systems like Kafka or RabbitMQ facilitate communication between different parts of your system by queuing messages, ensuring that even if parts of your system go down, the messages will eventually be processed.
- Logging and Monitoring:
  - Logging is crucial for tracking application behavior and debugging issues. Monitoring tools help keep track of application performance and resource usage, alerting you to potential problems before they impact users.
- Microservice Implementation:
  - As applications grow, breaking them down into microservices—smaller, independent services that work together—can make them easier to manage and scale.

Introduction to Microservices:¶

Monolithic Architecture:
- In the early stages of a project, it's common to implement everything within a single codebase or repository. This is known as monolithic architecture.
- While this approach is simple and works well for small applications, it can become problematic as the application grows. For example, a new developer might find it challenging to understand the entire codebase, and making changes can become increasingly risky and time-consuming.
Microservices Architecture:
- To address these challenges, companies often move to a microservices architecture as they grow. In this architecture, different functionalities of the application are split into separate services, each with its own codebase and possibly its own database.
- Example:
  - A large ecommerce platform might have separate services for handling user accounts, managing the product catalog, processing payments, and so on.
- These services communicate with each other through network calls, usually via REST APIs. This modular approach makes it easier to develop, test, and deploy individual components of the application independently.
Illustrations:
- In a microservices architecture, different services, potentially written in different programming languages, communicate via APIs, allowing for flexibility and scalability.

The Need for Frameworks:¶

The Problem:
- Imagine you had to write all the code required to perform these tasks—like setting up APIs, handling database connections, implementing logging, and managing microservices—from scratch for every project. This would be extremely time-consuming and error-prone.
The Solution – Frameworks:
- Frameworks are pre-built libraries or toolsets that provide developers with standardized ways of performing common tasks. Instead of reinventing the wheel every time, you can use these frameworks to quickly implement functionality that's been tried, tested, and optimized by other developers.
Benefits of Frameworks:
- Efficiency: They save time by providing ready-made solutions for common problems.
- Standardization: They enforce best practices and design patterns, making your code more maintainable and easier for others to understand.
- Security: Many frameworks have built-in security features, helping you avoid common vulnerabilities.
Examples of Frameworks by Language:
- Java:
  - Spring and Dropwizard are popular frameworks for building robust, scalable applications.
- Python:
  - Django and Flask are widely used for web development, with Django being more feature-rich and Flask being lightweight and flexible.
- C#:
  - .NET Framework is the go-to for building Windows applications and services.
- Go:
  - Gin is a web framework designed for building fast, reliable APIs.
- Ruby:
  - Ruby on Rails is a full-stack framework that emphasizes convention over configuration, making it quick to get started with.

Market Focus:¶

Why Java and Spring?
- because these technologies dominate the market. Approximately 80% of backend development jobs require proficiency in Java, with Spring being the most sought-after framework in the Java ecosystem. By mastering Java and Spring, you'll be well-equipped to apply for a broad range of positions in the software industry.

Why Spring?¶

Overview:¶

Spring Framework:
- Spring is an open-source application development framework for Java. It provides a comprehensive programming and configuration model for modern Java-based enterprise applications.
- Types of Applications:
  - With Spring, you can build different types of applications, including:
  - Command Line Applications: Simple programs that can be run in the terminal.
  - Terminal Applications: More complex applications that also run in the terminal but may interact with databases, file systems, and other services.
- Web Servers: Applications that serve web pages and provide RESTful APIs.
Enterprise-Grade Applications:
- When we say Spring is suited for enterprise-grade applications, we mean that it’s designed with large-scale, high-performance applications in mind. These applications require features like:
  - Scalability: The ability to handle increasing amounts of work by adding resources, such as additional servers.
  - Security: Protecting sensitive data and ensuring that only authorized users have access to certain features.
Spring Modules: Spring is modular, meaning you can pick and choose the components you need for your application.
Spring Core: This module is the heart of the framework, providing the essential features like dependency injection and aspect-oriented programming.
Spring Web: For building web applications, including RESTful services.
Spring Data: Simplifies database access, particularly in Java.
Spring Security: Provides authentication and authorization for securing your applications.
Spring Cloud: Helps with developing distributed systems and microservices.
Visualization:
- A visual representation of how Spring Core interacts with other Spring modules to create a fully functional application.

Challenges with Traditional Spring:¶

Configuration Complexity:
- In traditional Spring applications, developers had to manually configure each module using XML files. This process was not only time-consuming but also prone to errors.
- Version Conflicts:
  - Different modules in Spring had their own versioning, and these versions often did not play well together. For instance, you might find that the version of Spring Web you’re using is incompatible with the version of Spring Security, leading to runtime errors and other issues.

Solution – Spring Boot:¶

Introduction to Spring Boot:
- Spring Boot was developed to address these challenges by providing a more streamlined and developer-friendly approach to building Spring applications.
- Main Features:
  - Pre-configured Setup: Spring Boot comes with sensible defaults that reduce the need for manual configuration.
  - Version Management: It manages the versions of different Spring modules, ensuring compatibility.
  - Quick Start: With Spring Boot, you can get a new Spring application up and running in minutes, allowing you to focus more on writing business logic than on configuration.

Spring Boot¶

What is Spring Boot?¶

Spring Boot’s Role:
- Spring Boot takes an opinionated view of Spring application development. This means that it makes certain assumptions about how your application should be configured, which allows it to provide a lot of functionality out of the box.
- Purpose:
  - It simplifies the process of setting up and running Spring applications, particularly for beginners or for those who want to develop applications quickly without getting bogged down in configuration details.

How Does Spring Boot Work?¶

Spring Boot Starters:
- Starters are a set of convenient dependency descriptors that you can include in your project. They bring in all the dependencies you need for a particular feature.
- Examples:
  - spring-boot-starter-web: Includes everything you need to build a web application, including Spring MVC and embedded Tomcat (a web server).
  - spring-boot-starter-security: Brings in all the necessary dependencies to add security features to your application, such as authentication and authorization.
Version Management:
- One of the key benefits of Spring Boot is that it manages the versions of all dependencies for you. This means you don’t have to worry about incompatibility between different Spring modules or other libraries.
Default Configurations:
- Spring Boot comes with default configurations for many settings, so you don’t have to manually configure them unless you want to change the defaults.
- Customization:
  - While Spring Boot makes it easy to get started, it also allows for full customization. If you don’t like the default configurations, you can override them with your own settings.

Advantages of Using Spring Boot:¶

Reduced Complexity:
- With Spring Boot, much of the boilerplate configuration is handled automatically, allowing developers to focus on building features rather than setting up infrastructure.
Faster Development:
- The combination of starters, version management, and default configurations allows you to build and deploy applications quickly.
Production-Ready Applications:
- Spring Boot applications are designed to be production-ready right out of the box, with features like metrics, health checks, and externalized configuration.

Details of Spring Core¶

Understanding Dependency Injection:¶

The Problem with Direct Dependency Creation:
- In a typical application, different classes often need to interact with a database. For example, you might have a LoginService, a SignupService, and a UserService, all of which need to interact with the database.
- Direct Dependency Example:
  - If each service creates its own database object like this:
```
Database db = new Database();
```
  - Changing the database implementation (e.g., from MySQL to PostgreSQL) would require you to modify every single service that interacts with the database. This approach leads to tightly coupled code, making it difficult to maintain and extend.
What is Dependency Injection?
- Dependency Injection (DI) is a design pattern where an object’s dependencies are provided externally, rather than the object creating them itself.
- Analogy:
  - Think of your application like a human body. If your body needs antibodies to fight a virus but doesn’t have enough, you inject antibodies externally. Similarly, instead of each class in your application creating its own dependencies, those dependencies are injected externally.

Implementing Dependency Injection:¶

Setter Injection Example:
- With setter injection, you pass the dependency (e.g., the database object) to the class via a setter method.
```
class Service {
    private Database db;
    public void setDatabase(Database db) {
        this.db = db;
    }
}
```
- Main File:
```
Service service = new Service();
service.setDatabase(new MySQLDatabase());
```
- Benefits:
  - This approach makes it easier to swap out dependencies, as the dependency is injected rather than created within the class.
Constructor Injection Example:
- Constructor injection is another method of dependency injection where dependencies are provided through a class constructor.
```
class Service {
    private final Database db;
    public Service(Database db) {
        this.db = db;
    }
}
```
- Main File:
```
Database db = new MySQLDatabase();
Service service = new Service(db);
```
- Advantages:
  - Constructor injection is generally preferred because it makes it clear that a class cannot function without its dependencies. This also allows for better testing and easier refactoring.

Summary of Dependency Injection:¶

Key Takeaways:
- Loosely Coupled Code: By using dependency injection, your code becomes loosely coupled, meaning each class is independent and can be reused or modified without affecting other parts of the application.
- Flexibility: DI allows you to easily swap out implementations of dependencies (e.g., switching from MySQL to PostgreSQL) without having to make widespread changes to your codebase.

Inversion of Control (IoC)¶

What is Inversion of Control?¶

Traditional Control Flow:
- In traditional programming, the flow of control is determined by the application code itself. For example, if you have a Main class that creates and manages all dependencies, the control flow is managed directly by your code.
Inversion of Control (IoC):
- IoC is a design principle where the control flow of a program is inverted, meaning that instead of the application code controlling everything, the control is handed over to a framework. In the context of Spring, IoC means that Spring takes over the management of object creation and dependency injection.
Dependency Injection as a Form of IoC:
- Dependency Injection is one way to achieve Inversion of Control. Instead of your application code manually creating dependencies, the Spring framework injects these dependencies automatically based on your configuration.

How IoC Works in Spring:¶

Annotations:
- In Spring, you can annotate your classes and methods to indicate how dependencies should be managed. For example:
```
@Component
public class MyService {
    @Autowired
    private MyRepository myRepository;
}
```
- Explanation:
  - Here, the @Component annotation tells Spring that this class should be managed by the Spring IoC container. The @Autowired annotation tells Spring to inject an instance of MyRepository into MyService.
Spring IoC Container:
- The IoC container is the core of the Spring Framework. It manages the lifecycle of beans (i.e., objects managed by Spring), resolves dependencies, and injects them wherever needed. The container uses metadata (like annotations or XML configuration) to understand how to manage the objects.

Practical Example of IoC:¶

Instructor Activity:
- To demonstrate IoC, run a simple Spring application in IntelliJ IDEA. Show how Spring automatically manages object creation, dependency injection, and overall application flow without requiring extensive configuration.
- Key Points:
  - Highlight how Spring takes care of wiring up the components, allowing you to focus on business logic rather than boilerplate code.

Benefits of IoC:¶

Simplified Development:
- IoC simplifies application development by managing the complex details of object creation and dependency management, allowing developers to focus on implementing features.
Enhanced Testability:
- Because dependencies are injected rather than created within classes, it becomes easier to write unit tests. You can mock dependencies during testing without needing to change your application code.