Is this for the RPC system?  I think you're making this a lot harder than it
needs to be.

On the server side, when someone wants to export a service, they will
construct a service implementation and pass it to your system.  The
com.google.protobuf.Service interface has methods getDescriptor(),
getRequestPrototype(), and getResponsePrototype(), to get the
ServiceDescriptor, request message class, and response message class
respectively.  So, you don't need to consult any tables.

On the client side, your RPC implementation should merely provide the user
with an object implementing com.google.protobuf.RpcChannel.  The caller then
calls MyServiceType.newStub(channel) to construct a type-safe stub.  The RPC
system does not need to know what kind of service it is.

2009/12/10 Romain François <francoisrom...@free.fr>

> On 12/09/2009 09:00 PM, Kenton Varda wrote:
>
>> Actually I don't think we need DescriptorPool in Java.  DescriptorPool
>> was primarily written for the purpose of memory management, but Java
>> handles that for us.  If all you need is the mapping aspect, just build
>> a Map<String, ServiceDescriptor> yourself and use it.
>>
>
> This is close to what I do now. Next question is : can I get hold of the
> java class that is associated with a Descriptor.
>
> From the service descriptor, I can get to the MethodDescriptor I am
> interested in, and then I can get the Descriptor of the input type of the
> method, but at that point I would like to create a builder for the input
> message. Should I also maintain a Map<String,Descriptor>
>
> One thing I thought of would be to go back to the file descriptor
> associated with the input message type descriptor, check the two java
> options, and use java reflection. would this work ?
>
> It is a shame the java class name is not the same as the message type full
> name.
>
>  True, in C++ there is the "global pool" which is automatically populated
>> with everything compiled into the binary.  This wouldn't work in Java
>> because classes are not loaded until they are first accessed, so there
>> is no way to populate this pool.  Besides, singletons are evil.  I
>> honestly wish that I'd never introduced the global pool in C++; it has
>> lead to too many subtle singleton problems.
>>
>> 2009/12/9 Jason Hsueh <jas...@google.com <mailto:jas...@google.com>>
>>
>>
>>    No, there isn't an equivalent to the DescriptorPool in Java. If you
>>    know the types that you want you can build a mapping yourself. Or if
>>    you'd be interested in porting the C++ DescriptorPool to java that
>>    would be great!
>>
>>    2009/12/9 Romain François <francoisrom...@free.fr
>>    <mailto:francoisrom...@free.fr>>
>>
>>
>>        Hello,
>>
>>        Given a service/method full name, I'd like to get hold of the
>>        ServiceDescriptor, or MethodDescriptor. In C++ I would use the
>>        DescriptorPool, but I don't see this in the java api.
>>
>>        Is there a way ?
>>
>>        Romain
>>
>
> --
> Romain Francois
> Professional R Enthusiast
> +33(0) 6 28 91 30 30
> http://romainfrancois.blog.free.fr
> |- http://tr.im/Gq7i : ohloh
> |- http://tr.im/FtUu : new package : highlight
> `- http://tr.im/EAD5 : LondonR slides
>
>

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