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In this section, we will guide you through the process of creating your first Spring Boot application. By the end of this lesson, you will have a basic Spring Boot application up and running. We will cover the following steps:

Setting Up Your Project
Understanding the Project Structure
Writing Your First Controller
Running Your Application

Setting Up Your Project

Using Spring Initializr

Spring Initializr is a web-based tool that helps you bootstrap a new Spring Boot project. Follow these steps to set up your project:

Navigate to Spring Initializr: Open your web browser and go to Spring Initializr.
Project Metadata: Fill in the project metadata:
- Project: Maven Project
- Language: Java
- Spring Boot: Choose the latest stable version
- Project Metadata:
  - Group: com.example
  - Artifact: demo
  - Name: demo
  - Description: Demo project for Spring Boot
  - Package name: com.example.demo
  - Packaging: Jar
  - Java: 11 (or your preferred version)
Dependencies: Add the following dependencies:
- Spring Web
Generate the Project: Click on the "Generate" button to download the project as a ZIP file.
Extract the ZIP: Extract the downloaded ZIP file to a directory of your choice.

Importing the Project into Your IDE

Open Your IDE: Open your preferred IDE (e.g., IntelliJ IDEA, Eclipse, or VS Code).
Import the Project: Import the extracted project as a Maven project.
- In IntelliJ IDEA: File -> Open and select the project directory.
- In Eclipse: File -> Import -> Existing Maven Projects and select the project directory.

Understanding the Project Structure

Once the project is imported, you will see the following structure:

demo
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com
│   │   │       └── example
│   │   │           └── demo
│   │   │               └── DemoApplication.java
│   │   └── resources
│   │       ├── application.properties
│   │       └── static
│   │       └── templates
│   └── test
│       └── java
│           └── com
│               └── example
│                   └── demo
│                       └── DemoApplicationTests.java
├── mvnw
├── mvnw.cmd
├── pom.xml
└── README.md

Key Files and Directories

DemoApplication.java: The main class that bootstraps the Spring Boot application.
application.properties: Configuration file for the application.
static: Directory for static resources (e.g., HTML, CSS, JavaScript).
templates: Directory for server-side templates (e.g., Thymeleaf, FreeMarker).
DemoApplicationTests.java: Class for writing unit tests.

Writing Your First Controller

Let's create a simple REST controller that returns a "Hello, World!" message.

Step-by-Step Guide

Create a New Controller Class: In the com.example.demo package, create a new Java class named HelloController.

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

Explanation

@RestController: This annotation marks the class as a REST controller.
@GetMapping("/hello"): This annotation maps HTTP GET requests to the sayHello method.
sayHello(): This method returns a simple "Hello, World!" message.

Running Your Application

Using Your IDE

Run the Application: In your IDE, locate the DemoApplication class and run it as a Java application.
- In IntelliJ IDEA: Right-click on DemoApplication and select Run 'DemoApplication'.
- In Eclipse: Right-click on DemoApplication and select Run As -> Java Application.

Using the Command Line

Navigate to the Project Directory: Open a terminal and navigate to the project directory.
Build the Project: Run the following command to build the project:

./mvnw clean install

Run the Application: Run the following command to start the application:

./mvnw spring-boot:run

Accessing the Application

Open Your Web Browser: Open your web browser and go to http://localhost:8080/hello.
Verify the Output: You should see the message "Hello, World!".

Conclusion

Congratulations! You have successfully created and run your first Spring Boot application. In this lesson, you learned how to:

Set up a new Spring Boot project using Spring Initializr.
Understand the basic project structure.
Create a simple REST controller.
Run the application and verify the output.

In the next module, we will dive deeper into Spring Boot basics, including annotations, dependency injection, and configuration.

Creating Your First Spring Boot Application

Setting Up Your Project

Using Spring Initializr

Importing the Project into Your IDE

Understanding the Project Structure

Key Files and Directories

Writing Your First Controller

Step-by-Step Guide

Explanation

Running Your Application

Using Your IDE

Using the Command Line

Accessing the Application

Conclusion

Spring Boot Course

Module 1: Introduction to Spring Boot

Module 2: Spring Boot Basics

Module 3: Building RESTful Web Services

Module 4: Data Access with Spring Boot

Module 5: Spring Boot Security

Module 6: Testing in Spring Boot

Module 7: Advanced Spring Boot Features

Module 8: Deploying Spring Boot Applications

Module 9: Performance and Monitoring

Module 10: Best Practices and Tips