What you want to do is create a Map<Descriptor, Message> which maps from
descriptors to default instances of each of your generated classes.  For

  Map<Descriptor, Message> myMap = new ...;
  myMap.put(FooMessage.getDescriptor(), FooMessage.getDefaultInstance());
  myMap.put(BarMessage.getDescriptor(), BarMessage.getDefaultInstance());
  myMap.put(BazMessage.getDescriptor(), BazMessage.getDefaultInstance());

Now when you have a descriptor desc and you want to create a Builder for
that type, you do:

  Message.Builder builder = myMap.get(desc).newBuilderForType();

When you call builder.build(), you will end up with a Message that can be
down-cast to your generated type.

DynamicMessage is meant to be used for types that aren't compiled in at all.
 So of course you can't cast from DynamicMessage to a generated class -- the
generated classes are not subclasses of DynamicMessage.

On Sat, Oct 31, 2009 at 7:57 AM, Martin Gilday <martingil...@gmail.com>wrote:

> I am trying to write a service in Java which will convert back and
> forth using protobufs.  The docs say that this should be easy as
> "Reflection is provided as part of the Message and Message.Builder
> interfaces".  However I cannot seem to find what this is referring to.
> I would like have a generic method which takes a Descriptor and a
> stream which gives back an instance of message which I can later cast
> to my desired type.  I have tried DynamicMessage from =
> DynamicMessage.parseFrom(descriptor, inputStream); but I get an
> exception when I attempt to cast this as my generate proto class.
> Is there a solution to this?
> Thanks,
> Martin.
> >

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