JAX-RS in relation to Jersey and JSRs

Question

I\'m trying to get my head around some concepts in Java:

1. JSR(s): describe specifications, but carry no actual implementations. E.g. http://jsr311.java.net/ is

Answer 1

1. —
2. One can download files from a variety of sources. To get the most official version of the JSR-311 specification go to its JCP download page. It's quite possible that you can't get a JAR file (with all the interfaces and stuff) from JCP pages, but still, this is the official source. (There are always nice PDFs of public drafts also!)
3. —
4. You're right, because Jersey contains the API defined by JSR-311, however I would add a compile dependency to the jsr311-api JAR file and add Jersey as runtime dependency. This creates a nice separation between API and implementation and you can swap out your JSR-311 implementation anytime [sic]. If you intend to use Jersey all the way include only Jersey. One less dependency in your POM.
5. If Jersey packages the same API as the jsr311-api JAR contains, it won't. If it packages something different, well, that would be awful! Maven will probably bark at compile time if one has a corrupt JSR-311 API on its classpath (I've already seen lots of java.lang.ClassFormatError: Absent Code attribute in method that ... errors, so it won't go unnoticed, that's for sure).

Other than these, you're right.