Protocol Buffers in Java: can we handle primitive arrays efficiently?

Question

I work with messages that contain a few attributes and an array of a thousand floating point values (double[]). When the messages are serialized with protocol buffers, thanks to the "packed=true" directive, the double values are aligned and stored compactly in the messages.

But by default the Java classes generated for that message represent the double array as an array list (!), boxing primitive double values into objects, scattering those objects in memory, while at the end I need the double[] representation for further aggregations...

Is there an option to generate classes that handle repeated primitive values as Java primitive arrays?

Answer 1

As explained here what is needed is versions of ArrayList which store unboxed values. Since java generics works only with objects(boxed types), an implementation should be needed for each primitive type. So you can use the one provided by Apache Commons Primitives.

Answer 2

After discussing this topic in several places, the answer is a clear no.

With protocol buffers the binary representation for vectors of numbers is efficient. But it is currently not possible with the Java implementation to efficiently deserialize those vectors (instead of primitive arrays you get collections of boxed numbers...)