How to convert Descriptors.Descriptor to Java class name?

[ondrej par]

Hi all,

is there a convenient way to extract the name of Java (generated) class that represents the Message from Descriptors.Descriptor?

What I need is a method with the following signature:
public Class<? extends Message> extractJavaClass(Descriptors.Descriptor d);

I can derive class name using file/message descriptors methods, but that seems quite difficult, since I have to take java_package_name and java_outer_class_name options into account, and I have to convert underscores in proto file name to camel case

Thanks for answer,
Ondrej

[Pherl Liu]

Quoted from our internal discussion by Kenton:

You should build a Map<Descriptor, Message> upfront, mapping every
descriptor you care about to the corresponding default instance.  Avoid
using Class objects because that will make your code incompatible with
DynamicMessage.  Using default instances instead avoids this problem and
should cover all the same use cases.

Note that it should be easy to write a function like:
  void populate(Message root, Map<Descriptor, Message> map);
which recursively populates the map with the given message type and all of
its dependencies.

In C++, we have a singleton MessageFactory::generated_factory() which
effectively provides a Descriptor -> default instance map for all
compiled-in types.  But, this leads to all the usual singleton problems, and
code that uses it is often needlessly incompatible with DynamicMessage.
 People like the idea of being able to look up any compiled-in type because
it seems convenient, but in practice the convenience is typically not very
large, whereas the loss of reusability can be a big problem down the road.

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