SpringBoot Chapter 1 : Folder Structure, POM & Building Hello World Application

In this post, we consider maven to be our choice of build and dependency management tool.

✨ 1. Spring Boot Project Folder Structure

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

Explanation of Key Files and Directories:

• src/main/java/: Our Java source code goes here. By default this is the path SpringBoot expects the production code to be in.

• src/main/resources/: Configuration files, templates, and static assets.

  • application.properties: App configuration (port, database, etc.)
  • static/: Public static files (e.g., HTML, CSS, JS)
  • templates/: Thymeleaf or other template engines
• src/test/java/: Unit and integration tests
• .mvn/ and mvnw, mvnw.cmd: Maven wrapper files (optional)
• pom.xml: Maven’s Project Object Model file. Central to the build and dependency system. This must be present at the root of the project, same level as src.
• README.md: Optional documentation.

Note: While src/main/java is conventional, Maven allows us to change it, but it’s highly recommended to follow this convention for compatibility and tooling support.

More about Maven standard directory layout : Introduction to the Standard Directory Layout

---

📂 2. Where Are All the Dependencies Stored?

When we build our project with Maven, it downloads all required dependencies (JAR files) into our system’s local Maven repository, not our project folder.

Default Location:

• Windows: C:\Users\<username>\.m2\repository
• Linux/macOS: /home/<username>/.m2/repository

Maven caches dependencies so they don’t need to be re-downloaded for every project. This makes builds faster and projects cleanr.

We can change the local repository location by editing the settings.xml file in .m2.

---

🔧 3. Understanding pom.xml in Depth

pom.xml is the backbone of a Maven-based Spring Boot project. More about POM

Sample pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>hello-spring</artifactId>
    <version>1.0.0</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.0</version>
    </parent>

    <properties>
        <java.version>17</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

Key Sections:

• groupId / artifactId / version: Define’s the project coordinates.
• parent: Inherits Spring Boot’s default setup (dependency versions, plugins).
• properties: Configures build-level settings like Java version.
• dependencies: Lists all needed libraries (e.g., web starter).
• build: Adds plugins; spring-boot-maven-plugin enables building executable JAR’s.

---

🚀 4. Let’s Build the Hello World Spring Boot Application

Step-by-step without using Spring Initializer:

1. Creating folder structre manually as shown above
2. Writing the main class:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

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

1. Adding pom.xml to the root of the project (as above)
2. Compile and run:

mvn clean install
java -jar target/<filename>.jar

• mvn clean install: Cleans old builds and compiles, tests, and packages the application into a JAR. The output is stored in /target folder

We can now hit http://localhost:8080 in the browser to see the message: Hello, Spring Boot!

---