Hello World Spring Boot API

A simple Spring Boot REST API application with debugging support in VS Code dev containers.

Prerequisites

• Docker
• Visual Studio Code with Dev Containers extension

Getting Started

1. Open in Dev Container

1. Open this folder in VS Code
2. When prompted, click "Reopen in Container" (or use Command Palette: Dev Containers: Reopen in Container)
3. Wait for the container to build and dependencies to install

2. Run the Application

Option A: Using Terminal

mvn spring-boot:run

Option B: Using VS Code Tasks

Press Ctrl+Shift+P (or Cmd+Shift+P on Mac) and select Tasks: Run Task → spring-boot:run

The application will start on http://localhost:8888

3. Test the API

Open your browser or use curl:

curl http://localhost:8888/

Expected response: Hello World! Current server time is: [timestamp]

Debugging with Breakpoints

Method 1: Direct Debug Launch (Recommended)

1. Open a Java file (e.g., src/main/java/com/example/helloworldapi/controller/HelloWorldController.java)

2. Set a breakpoint:

   • Click on the left margin (line number gutter) next to the line where you want to pause
   • A red dot will appear indicating the breakpoint is set
   • Example: Set a breakpoint on line 15 in HelloWorldController.java (the return greeting; line)

3. Start debugging:

   • Press F5 (or click Run → Start Debugging)
   • Select "Debug Spring Boot App" from the configuration dropdown if prompted
   • Wait for the application to start (you'll see debug controls appear at the top)

4. Trigger the breakpoint:

   • Open your browser or use curl to hit the endpoint:

     curl http://localhost:8888/

   • The debugger will pause at your breakpoint
   • You can now:
     • Inspect variables in the Variables panel
     • Step through code using the debug toolbar (Step Over, Step Into, Step Out)
     • View the call stack
     • Evaluate expressions in the Debug Console

5. Continue execution:

   • Press F5 or click the Continue button to resume

Method 2: Attach to Running Process

If you already have the app running and want to attach the debugger:

1. Start the app with debug enabled:

   mvn spring-boot:run -Dspring-boot.run.jvmArguments="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005"

2. Attach the debugger:

   • Press Ctrl+Shift+D to open the Run and Debug view
   • Select "Attach to Remote Spring Boot" from the dropdown
   • Press F5 or click the green play button

3. Set breakpoints and test as described above

Debug Configuration

The project includes pre-configured debug settings in .vscode/launch.json:

• Debug Spring Boot App: Launches the application in debug mode
• Attach to Remote Spring Boot: Attaches to an already running application on port 5005

Project Structure

.
├── src/
│   └── main/
│       ├── java/
│       │   └── com/example/helloworldapi/
│       │       ├── HelloWorldApiApplication.java    # Main application class
│       │       └── controller/
│       │           └── HelloWorldController.java    # REST controller
│       └── resources/
│           └── application.properties
├── pom.xml                                          # Maven configuration
└── .devcontainer/                                   # Dev container configuration

Ports

• 8888: Spring Boot application
• 5005: Java debug port (JDWP)

Technology Stack

• Java 21
• Spring Boot 3.4.0
• Maven 3.9.6

GitHub Actions CI/CD

This project includes a GitHub Actions workflow that automatically builds and tests the application on every push or pull request to main branches.

What the workflow does:

1. Sets up JDK 21
2. Builds the project with Maven
3. Runs all tests
4. Packages the application as a JAR
5. Uploads the built artifact

The workflow configuration is in .github/workflows/maven-build.yml.

Troubleshooting

Breakpoints not working?

• Ensure you started the app using the debug configuration (F5), not just mvn spring-boot:run
• Check that the red dot appears solid (not hollow) when you set a breakpoint
• Verify the Java extension pack is installed and active

Port already in use?

# Find and kill the process using port 8888
lsof -ti:8888 | xargs kill -9

Application won't start?

# Clean and rebuild
mvn clean install

Additional Resources

• Spring Boot Documentation
• VS Code Java Debugging
• Maven Documentation