jd-cli target.jar -od output -g ALL
JD-GUI has the ability to batch export class files into .java file, zipped in a jar file.
however, this feature is not controlled by command line, but mouse clicking, this is not stable and sometimes will be stuck.
You can use jd-cli https://github.com/kwart/jd-cli/releases/tag/jd-cli-1.2.0
prepare your .jar file (containing classes ) (target.jar )
input: jd-cli target.jar -od jar_result -g ALL
and you will get a zipped java source code file.