[jax-rs-spec users] [jsr339-experts] ParamConverter and Collections

From: Sergey Beryozkin <>
Date: Wed, 13 Aug 2014 22:11:55 +0100

Hi Marek

Can you please be very nice tomorrow :-) and reply to the following:

A CXF user is wondering if CXF is compliant or not with respect to the
way it treats collections and ParamConverters.


public Response get(@QueryParam("a") MyAClass a);

ParamConverterProvider.getConverter(MyAClass.class, MyAClass.class,

would return the converter.

Now, next we have

public Response get(@QueryParam("a") List<MyAClass> a);

The user expects that ParamConverterProvider is asked to return a
converter for List<MyAClass>.

I said no, there was an agreement that the runtime was dealing with
managing the actual Lists or Sets, and ParamConverterProvider would only
be asked to provide a converter for MyAClass.

My other argument was that if the runtime were to ask to provide the
list/set converters then, given a query like "?a=2&a=4", the runtime
would have to pass the actual "a=2&a=4" String to the converter
(possibly re-created by the runtime in case the original query is more
involved, with multiple 'a' being mixed with other parameters) for it to
parse it in order to convert to List/Set. This appears to be
fundamentally wrong to me: this would mean that the same converter would
also have to be prepared to parse "a=2;a=4" to support Matrix parameter
lists. No idea how would one get the converters to convert a list of
headers to List/Set, what the runtime would pass to
converter.fromString() in case of multiple headers ?

To summarize, I think it is the job of the runtime to take care of
managing the actual lists/sets holding multiple parameters.

Does it Jersey do it differently ? Bill, what about RestEasy ?

Thanks, Sergey