@Override
  public Credential getCredential(String alias) throws AmbariException {
    if (alias == null) {
      return null;
    } else {
      lock.lock();
      try {
        return getCredential(loadCredentialStore(), alias);
      } finally {
        lock.unlock();
      }
    }
  }
Retrieves the specified credential from this CredentialStore
<p/>
This implementation is thread-safe, allowing one thread at a time to access the credential store.

@param alias a string declaring the alias (or name) of the credential
@return a Credential or null of not found
@throws AmbariException if an error occurs while retrieving the new credential
ambari-server/src/main/java/org/apache/ambari/server/security/encryption/AbstractCredentialStore.java