Java - DynamicMessage and FileDescriptorProto

[yoave]

Hi all,

I've got 2 questions:

1. how do I generate a Descriptor from a FileDescriptorProto in Java?
In cpp, I'm using DescriptorPool class's 'BuildFile()'
functionality.

2. how do I generate a Dynamic Message from a Descriptor in Java?
In cpp, I'm using DynamicMessageFactory class's 'GetPrototype()'
functionality.

thanks

[Pherl Liu]

Take a look at com.google.protobuf.Descriptors and com.google.protobuf.DynamicMessage

On Mon, Jul 18, 2011 at 8:20 AM, yoave <eina...@gmail.com> wrote:

Hi all,

I've got 2 questions:

1. how do I generate a Descriptor from a FileDescriptorProto in Java?
  In cpp, I'm using DescriptorPool class's 'BuildFile()'
functionality.

Descriptors.FileDescriptor.buildFrom()

2. how do I generate a Dynamic Message from a Descriptor in Java?
  In cpp, I'm using DynamicMessageFactory class's 'GetPrototype()'
functionality.

DynamicMessage.newBuilder(descirptor)

 

thanks

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[Giancarlo Frison]

There is this example that I'm approaching to re-implement
http://flori.posterous.com/dynamically-creating-protocol-buffer-objects

a question:

How to handle repeated fields? How can you describe them in the
fieldDescriptor?

[Pherl Liu]

Not sure if I understand your question correctly. You can set the label in FieldDescriptorProto:

LABEL_OPTIONAL = 1;

LABEL_REQUIRED      = 2;
LABEL_REPEATED      = 3;

[Giancarlo Frison]

Thank you very much Pherl!

An another question. What about not-primitive fields, or message
fields?

when I add fields I do:

DescriptorProtos.DescriptorProto.Builder desBuilder
....
DescriptorProtos.FieldDescriptorProto.Builder fd1Builder =
DescriptorProtos.FieldDescriptorProto.newBuilder()
.setName(fieldName).setNumber(i+
+).setType(type).setLabel(label);
desBuilder.addField(fd1Builder.build());

with message typed field I set type as
'DescriptorProtos.FieldDescriptorProto.Type.TYPE_MESSAGE'. How do I
describe the field type?
I mean, I suppose to describe the field with a inner
'DescriptorProtos.DescriptorProto.Builder', is it correct? How I can
do to describe a complex type field?

Thanks!

On Jul 26, 8:21 pm, Pherl Liu <liuj...@google.com> wrote:
> Not sure if I understand your question correctly. You can set the label in
> FieldDescriptorProto:
>
> LABEL_OPTIONAL = 1;
>
> LABEL_REQUIRED      = 2;LABEL_REPEATED      = 3;
>

[Robert]

Hi,

you either call setType() for primitive types or setTypeName(String)
for referenced messages.
You pass in the name of the message.

Kind regards,
Robert

[Giancarlo Frison]

if I call setTypeName(messageName), how protobuf match the name with
related Descriptor?
How can I map messageName and the descriptor of the type?

[Jason Hsueh]

The descriptor building libraries handle cross linking. The message type name must be defined in either the same file, or be available through one of the file's imports.

[Robert]

You have to define the name when constructing the DescriptorProto.
I have done this myself lately but unfortunately I am currently not in
the office.
But I can send you an example tomorrow of you like.

Kind regards
Robert

[Pherl Liu]

Take a look at the buildFrom() method. You need to provide an array of FileDescriptor as dependencies. If one of your message field is a complex type, you should build that complex type first, and pass the built FileDescriptor object to the buildFrom() in the dependencies array.

[Giancarlo Frison]

on the field type descriptor previously create i set name as:
b2.setName(typename)

in the container class (which has reference the b2 field) I setup the
field as:
fb = DescriptorProtos.FieldDescriptorProto.newBuilder()
.setName(fieldName).setNumber(i+
+).setLabel(label).setTypeName(typename);
b1.addField(fb.build());

For creating the b1 descriptor, first I generate the descriptor of b2
then:
d1 = b1.build();
fdp1 =
DescriptorProtos.FileDescriptorProto.newBuilder().addMessageType(d1).build();

but I get an error because fdp1.getDependenciesCount()==0
(Descriptors.java:233) Dependencies passed to
FileDescriptor.buildFrom() don't match those listed in the
FileDescriptorProto.

thrown here:
dynamicDescriptor = Descriptors.FileDescriptor.buildFrom(fdp1, fds);

(fds is array of 1, the b2 descriptor)

Why the d1 builder doesn't have the dependency defined adding the
complex typed field?

Thanks!!

Ps.: Robert, it's very kind of you whether send me the related
snippet. Thank you

On Jul 27, 8:10 pm, Pherl Liu <liuj...@google.com> wrote:
> Take a look at the buildFrom() method. You need to provide an array of
> FileDescriptor as dependencies. If one of your message field is a complex
> type, you should build that complex type first, and pass the built
> FileDescriptor object to the buildFrom() in the dependencies array.
>

[Robert]

Hi,

I do only create one FileDescriptor instance that contains all message
definitions, because they are all constructed dynamically.
For creating the FileDescriptorProtoBuilder I call:
FileDescriptorProto.Builder fileDescriptorProtoBuilder =
FileDescriptorProto.newBuilder();
Then I create all the message protos by calling (here A and B):
DescriptorProto.Builder messageProtoBuilderA =
DescriptorProto.newBuilder();
messageProtoBuilderA.setName( "A" );
DescriptorProto.Builder messageProtoBuilderB =
DescriptorProto.newBuilder();
messageProtoBuilderB.setName( "B" );

If message A references message B using field f I call:
messageProtoBuilderA.addFieldBuilder()
.setName("f")
.setNumber(2)
.setTypeName("B");

Then I add the message protos to the file descriptor:
fileDescriptorProtoBuilder.addMessageType(messageProtoBuilderA);
fileDescriptorProtoBuilder.addMessageType(messageProtoBuilderB);

Finally I create the file descriptor using:
FileDescriptorProto fileDescriptorProto =
fileDescriptorProtoBuilder.build();
FileDescriptor fileDescriptor =
FileDescriptor.buildFrom(fileDescriptorProto, new FileDescriptor[0]);

Now I can create concrete messages by calling:
Builder messageA =
DynamicMessage.newBuilder( fileDescriptor.findMessageTypeByName("A") );
Builder messageB =
DynamicMessage.newBuilder( fileDescriptor.findMessageTypeByName("B") );

messageA.setField(
fileDescriptor.findMessageTypeByName("A").findFieldByName("f"),
messageB.build() );

I hope I did not add any errors when abstracting the code and that I
understood your problem correctly.

Kind regards,
Robert

On 28 Jul., 14:35, Giancarlo Frison <gfri...@chelab.com> wrote:
> on the field type descriptor previously create i set name as:
> b2.setName(typename)
>
> in the container class (which has reference the b2 field) I setup the
> field as:
> fb = DescriptorProtos.FieldDescriptorProto.newBuilder()
>                 .setName(fieldName).setNumber(i+
> +).setLabel(label).setTypeName(typename);
> b1.addField(fb.build());
>
> For creating the b1 descriptor, first I generate the descriptor of b2
> then:
> d1 = b1.build();
> fdp1 =

> DescriptorProtos.FileDescriptorProto.newBuilder().addMessageType(d1).build(­);

> > >http://groups.google.com/group/protobuf?hl=en.- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

[Giancarlo Frison]

Perfect, it works!

Thank you Robert, Pherl and everyone for the help.

> > > >http://groups.google.com/group/protobuf?hl=en.-Zitierten Text ausblenden -