Protoc: How to generate multiple Java source files?

Question

After compiling a large Protobuf definition I am getting a 6 MB Java source code file.

Because of its size working with that file is a big pain as I develop in Eclipse and Eclipse totally stalls/crashes whenever I open that file.

Is there a way to let protoc generate multiple Java source code files instead of one big file?

Answer 1

Actually, there is. It's not documented, but you can add a line to your .proto file like this:

option java_multiple_files = true;

This will put each top-level message type from the .proto file into an independent .java file. Note that you'll of course have to update all your code to import these classes from their new locations. Note also that protoc will still generate the "outer" class it did before, just without the inner classes nested within it. The outer class is still the place to go to get the file's descriptor, top-level extensions, and other non-class things.

All that said, if you have a .proto file that big, I strongly recommend splitting up the .proto file itself into smaller files that import each other.