public ExtensionInfo getExtension(String name, String version) {
    return extensionMap.get(name + StackManager.PATH_DELIMITER + version);
  }
Obtain the extension info specified by name and version.

@param name     name of the extension
@param version  version of the extension
@return The extension corresponding to the specified name and version.
        If no matching stack exists, null is returned.
ambari-server/src/main/java/org/apache/ambari/server/stack/StackManager.java