jarsigner prints invalid digest/signature algorithm warnings if keysize is weak/disabled

For example, this is a JAR signed with a 1024-bit key:

jarsigner -signedjar signeda.jar -sigalg SHA256withRSA a.jar e1
jar signed.

Warning:
The SHA-256 algorithm specified for the -digestalg option is considered a security risk. This algorithm will be disabled in a future update.
The SHA256withRSA algorithm specified for the -sigalg option is considered a security risk. This algorithm will be disabled in a future update.
The RSA signing key has a keysize of 1024 which is considered a security risk. This key size will be disabled in a future update.
The signer certificate will expire within six months.
No -tsa or -tsacert is provided and this jar is not timestamped. Without a timestamp, users may not be able to validate this jar after the signer certificate's expiration date (2022-01-23).