public Collection<String> getListeners() {
        return listeners;
    }
Returns the classnames of all listener classes within the extension.
These classnames are defined within the manifest by the "listeners"
property as an array of strings, where each string is a listener
class name.

@return
     A collection of classnames for all listeners within the extension.
guacamole/src/main/java/org/apache/guacamole/extension/ExtensionManifest.java