openssl pkcs12 -export -in  public.pem -inkey private.pem -out noodle.p12 -name domain.tld -CAfile chain.pem -caname root -chain
keytool -importkeystore -srckeystore noodle.p12 -destkeystore noodle.jks -deststoretype jks -srcstoretype pkcs12

Official keytool manual

Official openssl manual