As of now we have the best and last resort of inferring JDK version from a Java jar. Best being inference from attribute in MANIFEST and last being from the bytecode version. We need a middle ground which is a closer approximation. #683 (comment) lists three ways to infer JDK version

1. From multi-release jars.
2. Date of release. Take the most recent Java LTS before the release date. Reference: https://github.com/google/oss-rebuild/pull/428/files#diff-c10e34c159428cdc2bc379349bd4cfa350a2ac9ab49a453e3ce6d097aa2c7507R280-R293
3. Check requireJavaVersion value of maven-enforcer-plugin.