Short Answer: It depends on the use case.

Command-line arguments in Spring Boot are not commonly used in everyday production deployments, but they are extremely useful in specific scenarios. Here’s a practical breakdown of when and why they matter:

✅ When Command-Line Arguments Are Useful

1. Quick Configuration Overrides (Without Changing Code)

📌 Overrides application.properties or application.yml dynamically.

• Use case: Adjusting configuration without modifying files (useful in CI/CD pipelines).
• Example: Change the port on startup:

  java -jar app.jar --server.port=9090

• Why?
  • Handy for testing different settings quickly.
  • Allows configurable deployments without modifying environment variables.

2. CI/CD & Dockerized Deployments

📌 Pass runtime parameters in Kubernetes, Docker, or cloud deployments.

• Use case: Injecting environment-specific configurations.
• Example (Docker Compose):

  services:
    app:
      image: my-spring-app
      command: ["java", "-jar", "app.jar", "--spring.profiles.active=prod"]

• Why?
  • Reduces reliance on config files in containerized environments.
  • Simplifies deployment workflows.

3. Feature Flags & A/B Testing

📌 Enable/disable features dynamically.

• Use case: Toggle features without restarting the app or redeploying.
• Example:

  java -jar app.jar --feature.toggle.newUI=true

• Why?
  • Enables A/B testing or gradual feature rollouts.
  • Useful in staging environments where different versions of a feature need to be tested.

4. Scripted Automation & Local Development

📌 Automate startup configurations for different environments.

• Use case: Running local environments with different configs.
• Example:

  mvn spring-boot:run -Dspring-boot.run.arguments="--debug=true"

• Why?
  • No need to edit application.properties every time you change an environment.
  • Simplifies local debugging and testing.

❌ When Command-Line Arguments Are NOT Ideal

1. Large-Scale Production Configurations

🚫 Why? Configurations should be managed via environment variables or external config files, not passed manually in the command line.

2. Sensitive Data (Passwords, API Keys)

🚫 Why? Command-line arguments are visible in process lists (ps aux), making them insecure for secrets.

✅ Use Environment Variables Instead:

  export DB_PASSWORD="mysecretpass"
  java -jar app.jar

3. Hard-to-Track Application Behavior

🚫 Why? If configurations change frequently via CLI arguments, debugging issues becomes harder.

✅ Use Configuration Files Instead for better visibility.

Final Verdict: Useful, but Not Always Essential

🔹 Takeaway

✅ Command-line arguments are handy for quick overrides and automation.

✅ They're useful in local development and CI/CD, but not ideal for production configs.

✅ For persistent settings, use application.properties or external configuration files instead.