Solution to OpenJDK’s “Connection error sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target” error
Today, I downloaded Open JDK 10 to test it against my NetCheck JAR file. It did not work. I got this error:
Connection error sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
It seems that the certificat store bundled with the open-source project does not have information on all CAs. So, I copied the certificate store files (cacerts and blacklisted.certs) from Oracle Java JRE directory and the problem got resolved.

Copy the cacert and blacklisted.certs files from Oracle Java.