🌍 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 configuration and optionally configured application packages
• 🚫 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>2.1.0</version>
</dependency>

Or from GitHub via JitPack:

<repositories>
  <repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
  </repository>
</repositories>

<dependency>
  <groupId>com.github.Skywalker690</groupId>
  <artifactId>spring-boot-starter-env-printer</artifactId>
  <version>2.1.0</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
2025-10-28T14:00:07.189Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : JAVA_HOME
2025-10-28T14:00:07.190Z  INFO --- [main] com.skywalker.envprinter.EnvPrinter : SERVER_PORT
...

3️⃣ Access via HTTP Endpoint

Endpoints are disabled by default. Set env.printer.endpoint-enabled=true to enable them, and protect them with authentication before exposing them.

# 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": "",
  "JAVA_HOME": "",
  "SERVER_PORT": ""
}

⚙️ Configuration

Basic Configuration

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

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

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

Project-only mode shows only environment variables referenced in configuration files and, when enabled, configured application packages:

# 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 ${ENV_VAR} placeholders
• Optionally detects @Value("${ENV_VAR}") and System.getenv("ENV_VAR") in configured compiled application packages

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	false	Enable/disable the HTTP endpoints. Disabled by default to avoid exposing configuration metadata.
env.printer.project-only	Boolean	true	Show only variables referenced in configuration files and optionally scanned compiled classes.
env.printer.show-values	Boolean	false	Show values instead of names only. Values may contain secrets.
env.printer.scan-compiled-classes	Boolean	false	Enable compiled-class scanning. Configure scan-packages when enabling.
env.printer.scan-packages	List	empty	Application package prefixes to scan, such as com.example.myapp.

📊 Endpoints

/env/env-printer (REST Controller, opt-in)

• 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, opt-in)

• 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: The HTTP endpoint is disabled by default. If enabled, protect it with authentication and authorization; show-values=true can expose secrets.

• 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
   • System.getenv("VARIABLE_NAME") calls in configured compiled classes

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.

Compiled-class scanning is disabled by default. To enable it safely, configure narrow application packages:

env:
  printer:
    scan-compiled-classes: true
    scan-packages:
      - com.example.myapp

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📄 License

Apache License 2.0

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Author: Sanjo (Skywalker)
Repository: spring-boot-starter-env-printer