Which configuration value actually wins?

Goal & mental model verified

Boot combines ordered property sources into an Environment and binds structured configuration. Later/higher-precedence sources can override earlier values. Profiles select configurations; they are not a security boundary.

Worked example · design exercise synthesis

For pricing.timeout, define a default and an environment-specific override. Bind settings into a typed ConfigurationProperties object and validate required values instead of scattering string lookups.

Engineering decision synthesis

Treat operational settings as external inputs and make startup fail clearly on invalid required configuration. This improves repeatability but demands disciplined deployment configuration.

Pitfall & diagnosis synthesis

An unexpected environment variable can override a checked-in value. Logging a full configuration dump can reveal secrets; a prod profile does not protect management endpoints.

Improve & validate synthesis

Document the effective source and precedence for critical settings. Review secrets access separately and test startup with missing, malformed and overridden values.