Get the major Java version on Java 8 and earlier and on Java 9 and later

JavaVersionSniffer.java

/*
 * RELEASED UNDER CC-0 (https://creativecommons.org/publicdomain/zero/1.0/):
 *
 * You can copy, modify, distribute and perform the work, even for commercial
 * purposes, all without asking permission.
 */
import java.lang.reflect.Method;

public class JavaVersionSniffer {

	public static int getMajorVersion() {
		try {
			// use Java 9+ version API via reflection, so it can be compiled for older versions
			Method runtime_version = Runtime.class.getMethod("version");
			Object version = runtime_version.invoke(null);
			Method version_major = runtime_version.getReturnType().getMethod("major");
			return (int) version_major.invoke(version);
		// do not catch `ReflectiveOperationException` because it does not exist in Java <7
		} catch (Exception ex) {
			// before Java 9 system property 'java.specification.version'
			// is of the form '1.major', so return the int after '1.'
			String versionString = System.getProperty("java.specification.version");
			return Integer.parseInt(versionString.substring(2));
		}
	}

}