Spring Boot properties ↔ YAML converter

What it handles

Most converters treat a properties file as a flat list of key=value pairs split on the first =. Real Spring Boot configuration is messier than that, so this one implements the java.util.Properties contract:

• All three separators — server.port=8080, server.port:8080 andserver.port 8080 are the same entry.
• Line continuations, so a long value broken across lines with a trailing \ is joined back together.
• Unicode and character escapes, so the \uCEE4\uD53C sequences older tooling leaves behind come back as readable text.
• Indexed keys. spring.profiles.active[0] and [1] become a YAML list, and app.users[0].name becomes a list of objects.
• Multi-document files. The #--- separator Spring Boot 2.4 introduced maps to and from the YAML --- separator.

Why some values come back quoted

A properties file has no types — every value is a string. YAML does have types, so a naive conversion silently changes data. These are the cases that matter in practice:

The last row is deliberate: Spring binds to the target type anyway, so 1.0 reaching a String field still arrives as "1.0". If you would rather nothing be inferred at all, tick Quote all values as strings.

Which format should you use

YAML is easier to read once a config grows, because shared prefixes collapse. Properties files win in two places worth knowing about: they are unambiguous about types, and@PropertySource cannot load YAML. Spring Boot reads both, and readsapplication.properties before application.yml when the same key appears in each.