How to Use Environment Variables in Spring Boot

In Spring Boot, you can use environment variables by referencing them in your application.properties or application.yml files with the ${VAR_NAME} syntax. Spring Boot automatically reads these variables at runtime, allowing you to configure your app without hardcoding sensitive or environment-specific data.

Syntax

Use environment variables in Spring Boot configuration files by enclosing the variable name in ${}. You can provide a default value using : if the environment variable is not set.

• ${VAR_NAME}: Reads the environment variable VAR_NAME.
• ${VAR_NAME:defaultValue}: Uses defaultValue if VAR_NAME is not set.

properties

spring.datasource.url=${DB_URL:jdbc:h2:mem:testdb}
spring.datasource.username=${DB_USER:sa}
spring.datasource.password=${DB_PASS:password}

Example

This example shows how to use environment variables to configure a database connection in Spring Boot. The app reads DB_URL, DB_USER, and DB_PASS from the environment or uses defaults if they are missing.

java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

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

@RestController
class ConfigController {
    @Value("${DB_URL:jdbc:h2:mem:testdb}")
    private String dbUrl;

    @GetMapping("/dbinfo")
    public String getDbInfo() {
        return "Database URL: " + dbUrl;
    }
}

Output

Database URL: jdbc:h2:mem:testdb

Common Pitfalls

• Not setting environment variables before running the app causes Spring Boot to use default values or fail if no default is provided.
• Using incorrect variable names or typos in ${VAR_NAME} will result in unresolved placeholder errors.
• For complex types, environment variables are always strings; conversion must be handled by Spring Boot or manually.
• Remember environment variables are case-sensitive on some systems.

properties

spring.datasource.password=${DB_PASS}
# If DB_PASS is not set, this causes an error

# Correct way with default:
spring.datasource.password=${DB_PASS:defaultPass}

Quick Reference

Tips for using environment variables in Spring Boot:

• Use ${VAR_NAME:default} to avoid errors if variables are missing.
• Set environment variables in your OS or container before starting the app.
• Use @Value annotation to inject variables into Spring beans.
• Check variable names carefully for typos and case sensitivity.

Key Takeaways

Use ${VAR_NAME} syntax in application.properties or application.yml to read environment variables.

Provide default values with ${VAR_NAME:default} to prevent startup errors.

Inject environment variables into Spring beans using @Value annotation.

Always set environment variables in your system or container before running the app.

Check for typos and case sensitivity to avoid unresolved placeholder errors.