public Collection<ExtensionInfo> getExtensions(String extensionName) throws AmbariException {
    Collection<ExtensionInfo> extensions = stackManager.getExtensions(extensionName);

    if (extensions.isEmpty()) {
      throw new StackAccessException("extensionName=" + extensionName);
    }

    return extensions;
  }
Convenience method to get stack info from a stack id
@param stackId
           the stack id
@return  the stack info
@throws AmbariException
ambari-server/src/main/java/org/apache/ambari/server/api/services/AmbariMetaInfo.java