ShowKey.java

import javax.crypto.SecretKey;
import java.io.FileInputStream;
import java.nio.channels.FileChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.security.KeyStore;

public class ShowKey {
    public static void main(String[] args) throws Exception {
        if (args.length != 3) {
            System.out.println("Usage: java ShowKey </path/to/jceks> <password> <alias>");
            System.out.println("Example java ShowKey /var/lib/knox/gateway/data/security/keystores/knoxsso-credentials.jceks knoxsecret pac4j.password");
            System.exit(1);
        }
        String fileName = args[0];
        char[] password = args[1].toCharArray();
        String alias = args[2];

        try (FileChannel fileChannel = FileChannel.open(Paths.get(fileName),StandardOpenOption.READ)) {
            fileChannel.lock(0L, Long.MAX_VALUE, true);
        }

        KeyStore ks = KeyStore.getInstance("JCEKS");
        try (FileInputStream fis = new FileInputStream(fileName)) {
            ks.load(fis, password);
            SecretKey secretKey = (SecretKey) ks.getKey(alias, password);
            System.out.println(new String(secretKey.getEncoded()));
        }
    }
}