javap ?
출처 : Java Class 버전
javap -verbose class | grep major
JDK 1.0 = major version 45
JDK 1.1 = major version 45
JDK 1.2 = major version 46
JDK 1.3 = major version 47
JDK 1.4 = major version 48
JDK 1.5 = major version 49
JDK 1.6 = major version 50
JDK 1.7 = major version 51