"keytool -printcert" is supposed to print info about certificate which was used to sign a jar file. It says "Not a signed jar file" if one of disabled algorithms (see "jdk.jar.disabledAlgorithms" security property) was used for jar signing.

Please see attached signed jars:
signed-app-md2-rsa-2048.jar - signed with MD2withRSA
signed-app-md5-rsa-2048.jar - signed with MD5withRSA

The following command doesn't work with JDK 9 b142:

keytool -printcert -jarfile signed-app-md5-rsa-2048.jar

It would be better if "-printcert" command printed info about singers even if they use disabled algorithms.