thanks for your quick reply.
Yes, exactly. In this case JAX-RS currently doesn't specify which one should be used.
Not sure if something like @DefaultProvider is flexible enough. Maybe this "default provider" vs "custom provider" use case is just one special case? I mean, it is always possible to have multiple exception mappers on the classpath if they are provided by different libraries. And in this case it would be nice to have some clear rules on how to handle this situation.
For filters and interceptors there is already javax.ws.rs.Priorities which contains constants which can be used for ordering. So this could also be used for exception mappers and param providers.
That wouldn't be a problem, because MVC will go final after JAX-RS and therefore could depend on JAX-RS 2.1.