Lazy implementation of MediaSupport classes

[romain-grecourt]

The code below should be implemented lazily for all MediaSupport implementations:

    @Override
    public Collection<MessageBodyReader<?>> readers() {
        return List.of(newReader());
    }

    @Override
    public Collection<MessageBodyWriter<?>> writers() {
        return List.of(newWriter());
    }

[tomas-langer]

@romain-grecourt could you please elaborate a bit, this issue is quite old and I am not sure it is still relevant. Thanks

[romain-grecourt]

This is about avoiding the creation of new operator instances for every invocation to readers() and writers(). I.e Use a list field and initialize it on the first call to readers() and writers().

DefaultMediaSupport can be improved:

• new operators are created every time readers() or writers() is invoked
• DefaultMediaSupport.create can use a LazyValue for the default
• MultiPartSupport.create() can use a LazyValue for the default

Using LazyValue with create() methods is odd, but it's a decent optimization as the operators are stateless. This pattern is implemented by JacksonSupport, JsonbSupport and JsonpSupport. We should update the javadoc to state that it's get or create rather than just create.