What version of javac built my jar?

Question

How can I tell what version of the Java compiler was used to build a jar? I have a jar file, and it could have been built in any one of three JDKs. We need to know exactly

Answer 1

There is no need to unpack the JAR (if one of the class names is known or is looked up e.g. using 7zip), so on Windows the following would be sufficient:

javap -cp log4j-core-2.5.jar -verbose org.apache.logging.log4j.core.Logger | findstr major