Igor's Techno Club
I was recently working on better support for .properties files in Jar.Tools. Probably every Java developer has worked with this format and knows that it's a simple one. So did I until I started implementing it. This is a kind of list of quirks and interesting cases I faced during this journey.
A backslash followed by trailing spaces still behaves as a continuation marker in practice. If the file ends right after that whitespace (no next line), it’s a broken continuation error.
All three lines receive a warning that includes the index of every occurrence (e.g., “Duplicate key ‘duplicate.key’ found at: line 2, line 5, line 8”). By contrast:
Why warn and not error? Real configs sometimes rely on “last one wins,” but it’s almost never intentional. A warning keeps you honest without breaking builds.
Properties files support \uXXXX escapes. That opens a whole Unicode can: invalid lengths, non‑hex digits, surrogate pairs for emoji, and “unknown” escapes.
