libprotobuf-java binary package in Ubuntu Focal amd64

 Protocol buffers are a flexible, efficient, automated mechanism for
 serializing structured data - similar to XML, but smaller, faster, and
 simpler. You define how you want your data to be structured once, then you can
 use special generated source code to easily write and read your structured
 data to and from a variety of data streams and using a variety of languages.
 You can even update your data structure without breaking deployed programs
 that are compiled against the "old" format.
 .
 Google uses Protocol Buffers for almost all of its internal RPC protocols and
 file formats.
 .
 This package contains the Java bindings for the protocol buffers. You will
 need the protoc tool (in the protobuf-compiler package) to compile your
 definition to Java classes, and then the modules in this package will allow
 you to use those classes in your programs.

Source package