Using both \u.... and html entities in properties file?

I'm stumbling upon a few xxx_fr.properties, xxx_en.properties, etc. files and I'm a bit surprised for they contain both html entities and \uxxxx escapings.

I guess the HTML entities are fine as long as these resources are served to something awaiting HTML but what about the \开发者_运维知识库uxxxx escaping?

Does Java specify that \uxxxx escaping are fine in .properties file?

Yes - see the documentation for load(Reader), which states

Characters in keys and elements can be represented in escape sequences similar to those used for character and string literals.

and then clarifies that

Only a single 'u' character is allowed in a Unicode escape sequence.

Hence a Unicode escape sequence containing a single 'u' character is definitely supported.

Note that there's nothing special going on here at loading time with HTML entities - the String & for example would simply be seen within Java as a String containing 5 characters. As you point out, this might be interpreted in a special way if it were output to some other component later.

On the other hand, the escape sequence \u0061 would be seen within Java as the single-character string 'a', and would be indistinguishable from the file having contained that character instead.

The \u type escaping is a standard Java way of representing Unicode characters. You can read about it in Java Internationalization FAQ. With "How do I specify non-ASCII strings in a properties file?" question being the one you're most interested in:

http://java.sun.com/javase/technologies/core/basic/intl/faq.jsp#properties-escape

And that's not Properties related only; you can use those in your typical Java code as well. See the Text Representation block:

http://java.sun.com/javase/technologies/core/basic/intl/faq.jsp#core-textrep