Configuration

Introduction

Configuration is how an app behaves differently in dev, staging and prod without code changes. Spring Boot reads from a precedence chain: command-line args > env vars > application-{profile}.yml > application.yml > defaults.

Understanding the topic

Three ways to read config:

• @Value("${stripe.api-key}") — single property; OK for ad-hoc.
• @ConfigurationProperties(prefix = "stripe") — type-safe binding to a record/class. Preferred.
• Environment bean — programmatic lookup.

Informative example

Type-safe config with a record:

@ConfigurationProperties(prefix = "stripe")
@Validated
public record StripeProps(
    @NotBlank String apiKey,
    @NotNull URI baseUrl,
    @DefaultValue("10s") Duration timeout
) {}

# application.yml
stripe:
  api-key: ${STRIPE_API_KEY}
  base-url: https://api.stripe.com
  timeout: 5s

Best practices

• Inject secrets via env vars; never commit them.
• Use @ConfigurationProperties + @Validated — fail fast on missing values.
• Prefer application.yml over .properties — nested, comments, multi-line.