JAX-RS in relation to Jersey and JSRs

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

JSR(s): describe specifications, but carry no actual implementations. E.g. http://jsr311.java.net/ is the "home" for "Java™ API for RESTful Web Services". It serves as a common reference for all implementations of JSR-311.
One can download the interfaces (?) of JSR-311 from http://mvnrepository.com/artifact/javax.ws.rs/jsr311-api, however, unless you are implementing JSR-311 by yourself these have no particular value?
JSR(s) will usually/always have a reference implementation. To find it you'll have to google "JSR XXX reference implementation" or see the specifications home page (e.g. http://jsr311.java.net/)
For JSR-311 this reference implementation is Jersey. Using maven you can get the jersey server from http://mvnrepository.com/artifact/com.sun.jersey/jersey-server/1.9. Since Jersey provides an implementation according to the interfaces found in http://mvnrepository.com/artifact/javax.ws.rs/jsr311-api, you only need to add Jersey as a dependency in your project and not the jsr311-api itself. (this applies to all JSR technologies?)
Putting both http://mvnrepository.com/artifact/javax.ws.rs/jsr311-api and http://mvnrepository.com/artifact/com.sun.jersey/jersey-server/1.9 as dependencies in your project will possibly cause classpath problems?

Am I completely off or onto someting?

Yes, this isn't anything new. Think about JDBC, java provides the interfaces (Connection, Statement, ResultSet etc) but it is up to database vendors to provide implementations.
If you're using a JSR-311 implementation like Jersey or Apache CXF then you'll annotate your classes with the javax.ws.rs annotations, such as @Path, @GET, @Produces etc. This is why you need to explicitly have JSR-311 as a maven dependency.
Yes, usually. Have a look at the JSR list on wiki.
You need both the JSR and the implementation. The annotations are in the JSR, the implementation provides supporting classes, such as com.sun.jersey.spi.container.servlet.ServletContainer.
No, it is necessary to have both as dependencies (see point 4); you won't get classpath conflicts.

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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!)
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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.
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.

来源：https://stackoverflow.com/questions/8476820/jax-rs-in-relation-to-jersey-and-jsrs

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