Java get CodeSigners from class

I'm running java 17 and calling class.getProtectionDomain().getCodeSource().getSigners() always returns null even though the associated jar is correctly signed. Does anyone know why this is and if there is a fix or another solution.

When checking the jarsigner the following gets returned, jarsigner -verify .\mcpaintball-1.5.1-R.jar

jar verified.

Warning:
This jar contains entries whose certificate chain is invalid. Reason: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
This jar contains entries whose signer certificate is self-signed.

Re-run with the -verbose and -certs options for more details.

I have tried to use both class.getSigners() and class.getProtectionDomain().getCodeSource().getCertificates() to no avail.
I was expecting to get the list of signers containing my signing information or at the very least the certificate.

Are there algorithms that java does not support that could be causing this issue.

I would suggest adding the self-signed cert which was used to sign the jar to your systems truststore.

Export certificate from the JAR file

keytool -exportcert -alias <signer> -keystore <keystore.jks> -storepass <password> -file signer.cer

Import to truststore

keytool -importcert -alias <signer> -keystore <cacerts.jks> -storepass <password> -file signer.cer

Replace values in brackets accordingly. keytool is available in jdk, so should work in windows.
After this verify signature.

It’s possible that your cacerts file is not in the JKS format.
The cacerts file is usually located in the
$JAVA_HOME/jre/lib/security/ directory.

You can check the format of your cacerts file using the following command:

keytool -list -v -keystore /path/to/cacerts

If cacerts file is not in the JKS format, you can convert it to JKS using the following command:

keytool -importkeystore -srckeystore /path/to/cacerts -destkeystore /path/to/cacerts.jks -deststoretype jks

Hope this helps.