Project structure walkthrough in Spring Boot

Introduction

A clear project structure helps you find and organize your code easily. It makes your Spring Boot app neat and simple to work on.

When starting a new Spring Boot application to keep code organized.

When adding new features and you want to know where to put files.

When working with a team so everyone understands the project layout.

When debugging or updating code and you need to find files quickly.

When preparing your app for deployment or sharing with others.

Syntax

Spring Boot

src
 ├── main
 │    ├── java
 │    │    └── com.example.project
 │    │         ├── controller
 │    │         ├── service
 │    │         ├── repository
 │    │         └── Application.java
 │    └── resources
 │         ├── application.properties
 │         └── static
 └── test
      └── java
           └── com.example.project
                └── ApplicationTests.java

src/main/java holds your Java code organized by packages.

src/main/resources contains config files and static assets like images or CSS.

Examples

Controllers handle web requests and responses.

Spring Boot

src/main/java/com/example/project/controller/UserController.java

Services contain business logic and operations.

Spring Boot

src/main/java/com/example/project/service/UserService.java

Repositories manage data access and database queries.

Spring Boot

src/main/java/com/example/project/repository/UserRepository.java

Configuration settings for your Spring Boot app.

Spring Boot

src/main/resources/application.properties

Sample Program

This is the main class that starts your Spring Boot app. It lives in the base package.

Spring Boot

package com.example.project;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

Important Notes

Keep your package names clear and consistent to avoid confusion.

Place test classes in src/test/java mirroring your main code packages.

Use resources/static for files like images, CSS, and JavaScript that your app serves.

Summary

Spring Boot projects have a standard folder layout to organize code and resources.

Main Java code goes under src/main/java with packages like controller, service, and repository.

Configuration and static files go under src/main/resources.

Practice

1. In a typical Spring Boot project, where should you place your main application Java files?

easy

A. src/resources/java

B. src/main/resources

C. src/test/java

D. src/main/java

Solution

1. Step 1: Understand Spring Boot folder roles

   The src/main/java folder is for main Java source code including the application entry point.

2. Step 2: Identify correct folder for main Java files

   Main application files should not be in resources or test folders, so src/main/java is correct.

3. Final Answer:

   src/main/java -> Option D

4. Quick Check:

   Main Java code = src/main/java [OK]

Hint: Main Java code always goes under src/main/java [OK]

Common Mistakes:

• Confusing resources folder with Java source folder
• Placing main code in test folder
• Using incorrect folder names like src/resources/java

2. Which file is commonly used to manage dependencies and build steps in a Spring Boot Maven project?

easy

A. pom.xml

B. application.properties

C. build.gradle

D. settings.xml

Solution

1. Step 1: Identify build tool for Maven projects

   Maven uses pom.xml to manage dependencies and build configuration.

2. Step 2: Differentiate from Gradle and config files

   build.gradle is for Gradle, application.properties is for app config, and settings.xml is not for dependencies.

3. Final Answer:

   pom.xml -> Option A

4. Quick Check:

   Maven build file = pom.xml [OK]

Hint: Maven uses pom.xml; Gradle uses build.gradle [OK]

Common Mistakes:

• Confusing application.properties with build files
• Mixing Gradle and Maven build files
• Thinking settings.xml manages dependencies

3. Given this Spring Boot project structure snippet, where will the test Java files be located?

src/
  main/
    java/
    resources/
  test/
    java/
    resources/

medium

A. src/main/resources

B. src/test/java

C. src/main/java

D. src/test/resources

Solution

1. Step 1: Understand test folder purpose

   The src/test/java folder is for Java test source files.

2. Step 2: Identify test Java files location

   Test Java files go under src/test/java, not in main or resources folders.

3. Final Answer:

   src/test/java -> Option B

4. Quick Check:

   Test Java code = src/test/java [OK]

Hint: Test Java files go in src/test/java folder [OK]

Common Mistakes:

• Putting test Java files in src/main/java
• Confusing test resources with test Java code
• Using src/main/resources for tests

4. You accidentally placed your application.properties file inside src/main/java. What problem will this cause?

medium

A. The application will fail to start due to missing config

B. The build will fail with a syntax error

C. The properties file will be ignored and default config used

D. The application.properties will be loaded correctly anyway

Solution

1. Step 1: Know where Spring Boot loads config files

   Spring Boot loads application.properties from src/main/resources or classpath root.

2. Step 2: Effect of wrong file location

   If placed in src/main/java, it won't be found and ignored, so defaults apply.

3. Final Answer:

   The properties file will be ignored and default config used -> Option C

4. Quick Check:

   Config files must be in resources, else ignored [OK]

Hint: Config files must be in resources folder to load [OK]

Common Mistakes:

• Assuming app fails to start immediately
• Thinking build fails due to config file location
• Believing misplaced properties still load

5. You want to add a new configuration file for your Spring Boot app that should be packaged inside the jar and accessible at runtime. Where should you place this file?

hard

A. src/main/resources/config

B. src/main/java/config

C. src/test/resources/config

D. src/main/resources/static

Solution

1. Step 1: Understand resource packaging in Spring Boot

   Files in src/main/resources are packaged inside the jar and available at runtime.

2. Step 2: Choose correct folder for config files

   Config files should be under src/main/resources/config to be included and organized.

3. Final Answer:

   src/main/resources/config -> Option A

4. Quick Check:

   Runtime config files go in src/main/resources [OK]

Hint: Put runtime config files in src/main/resources folder [OK]

Common Mistakes:

• Placing config files in src/main/java which is for code
• Using test resources folder which is not packaged
• Putting config in static folder meant for web assets