🌍 Spring Boot Starter Env Printer

A lightweight custom Spring Boot starter designed to automatically print environment variables at application startup — and optionally expose them via HTTP endpoint for easier debugging and configuration visibility.

This starter is useful for developers who deploy applications across multiple environments (like local, staging, or production) and need quick insight into what environment variables are available during runtime — without manually logging or debugging them.

✨ Features

• 🚀 Auto-prints environment variables at application startup with proper SLF4J logging
• 🌐 Actuator-independent HTTP endpoint at /env/env-printer - no actuator dependency required
• 🔍 Optional actuator endpoint at /actuator/envprinter when actuator is present
• 🎯 Smart project-only mode - scans your entire project to show only environment variables actually used
• 🚫 Hardcoded OS exclusions - automatically hides 50+ common OS-specific variables (APPDATA, TEMP, etc.)
• ⚙️ Highly configurable via application.properties or application.yml
• 📦 Zero configuration required - works out of the box with sensible defaults
• 🔤 Sorted output - environment variables are sorted alphabetically for easy reading
• 🎨 Spring Boot 3 compatible - uses modern autoconfiguration format

🚀 Quick Start

1️⃣ Add Dependency

<dependency>
    <groupId>io.github.skywalker690</groupId>
    <artifactId>spring-boot-starter-env-printer</artifactId>
    <version>1.0.0</version>
</dependency>

2️⃣ Run Your Application

Environment variables will automatically be printed at startup (OS-specific variables excluded):

2025-10-28T14:00:07.184Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : ===============================
2025-10-28T14:00:07.184Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : 🌍 Environment Variables
2025-10-28T14:00:07.185Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : ===============================
2025-10-28T14:00:07.188Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : DATABASE_URL = jdbc:postgresql://localhost:5432/mydb
2025-10-28T14:00:07.189Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : JAVA_HOME = /usr/lib/jvm/java-17
2025-10-28T14:00:07.190Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : SERVER_PORT = 8080
...

3️⃣ Access via HTTP Endpoint

# Actuator-independent endpoint (works without Spring Boot Actuator)
curl http://localhost:8080/env/env-printer

# Or if you have Spring Boot Actuator
curl http://localhost:8080/actuator/envprinter

Returns:

{
  "DATABASE_URL": "jdbc:postgresql://localhost:5432/mydb",
  "JAVA_HOME": "/usr/lib/jvm/java-17",
  "SERVER_PORT": "8080"
}

⚙️ Configuration

Basic Configuration

# Enable or disable the env printer (default: true)
env.printer.enabled=true

# Enable or disable the HTTP endpoint (default: true)
env.printer.endpoint-enabled=true

🎯 Project-Only Mode (Show Only Variables Used in Your Project)

Enable project-only mode to scan your entire project and show only environment variables that are actually referenced:

# Scan project files and show only used environment variables
env.printer.project-only=true

What does it scan?

• application.properties and application.yml files
• Finds ${ENV_VAR} placeholders
• Detects @Value("${ENV_VAR}") annotations
• Detects System.getenv("ENV_VAR") calls

Example:

If your application.yml contains:

database:
  url: ${DATABASE_URL}
  username: ${DB_USER}
  
server:
  port: ${SERVER_PORT:8080}

With project-only=true, only DATABASE_URL, DB_USER, and SERVER_PORT will be displayed (if they exist in the environment).

Full Configuration Example

# Basic settings
env.printer.enabled=true
env.printer.endpoint-enabled=true

# Show only variables actually used in project
env.printer.project-only=true

# Show env values
env.printer.show-values=true

spring.application.name=my-spring-app

YAML Configuration:

env:
  printer:
    enabled: true
    endpoint-enabled: true
    project-only: true
    show-values: false

🛠️ Configuration Properties Reference

Property	Type	Default	Description
env.printer.enabled	Boolean	true	Enable/disable the environment printer. When disabled, no environment variables will be printed at startup and the endpoint will not be available.
env.printer.endpoint-enabled	Boolean	true	Enable/disable the HTTP endpoint for environment variables. When disabled, only startup logging will occur.
env.printer.project-only	Boolean	true	Scan project files to show only environment variables actually referenced in configuration files and source code. When enabled, provides the most relevant view of your application's environment.
env.printer.show-values	Boolean	false	Controls whether actual values of environment variables are displayed. When disabled, only variable names are shown to protect sensitive information.

📊 Endpoints

/env/env-printer (REST Controller)

• Type: Standard REST endpoint
• Requires: Spring Web (no actuator needed)
• Access: GET http://localhost:8080/env/env-printer
• Response: JSON map of filtered environment variables

/actuator/envprinter (Actuator Endpoint)

• Type: Spring Boot Actuator endpoint
• Requires: Spring Boot Actuator dependency
• Access: GET http://localhost:8080/actuator/envprinter
• Response: JSON map of filtered environment variables
• Note: Requires actuator endpoints to be exposed

📋 Requirements

• Java 17 or higher
• Spring Boot 3.2.4 or higher
• Spring Web (for REST controller endpoint)
• (Optional) Spring Boot Actuator for actuator endpoint

🎯 Use Cases

1. Development - See Only Variables Your App Uses

env.printer.project-only=true

Automatically scans and shows only ${...} references from config files.

2. Debugging - See All Non-OS Variables

env.printer.project-only=false

Shows all environment variables except OS-specific ones.

3. Production - Disable Completely

env.printer.enabled=false

4. CI/CD - Verify Environment Setup

env.printer.enabled=true
env.printer.project-only=true

Check logs to verify all required variables are set.

🔒 Security Note

Be careful when exposing environment variables via HTTP endpoints in production. Consider: Note: If using Spring Security don't forget about SecurityConfig to permit endpoint

• Using project-only=true to limit exposure
• Securing endpoints with authentication
• Disabling in production with env.printer.enabled=false
• The starter automatically hides OS-specific variables

📝 How Project Scanning Works

When project-only=true:

1. Scans configuration files in classpath:

   • application*.properties
   • application*.yml, application*.yaml

2. Extracts variable references:

   • ${VARIABLE_NAME} placeholders
   • ${VARIABLE_NAME:default} with defaults
   • @Value("${VARIABLE_NAME}") annotations (limited in compiled code)
   • System.getenv("VARIABLE_NAME") calls (limited in compiled code)

3. Filters environment:

   • Shows only variables found in step 2
   • Excludes hardcoded OS variables
   • Returns sorted alphabetically

Performance: Scanning happens once at startup and results are cached.

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📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

🤝 Contributing

Contributions, issues, and feature requests are welcome!
Check out the CONTRIBUTING.md file and feel free to submit a PR.

⭐ Show Your Support

If you find this starter useful, please star the repository to help others discover it! 👉 https://github.com/Skywalker690/spring-boot-starter-env-printer

🔍 Useful Links

• 📦 Maven Central: https://search.maven.org/artifact/io.github.skywalker690/spring-boot-starter-env-printer
• 🧑‍💻 GitHub Repo: https://github.com/Skywalker690/spring-boot-starter-env-printer
• 📝 Issue Tracker: https://github.com/Skywalker690/spring-boot-starter-env-printer/issues

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Author: Sanjo (Skywalker690)