private PluginRegistryBean loadRegistry(URI registryUrl) {
        PluginRegistryBean fromCache = registryCache.get(registryUrl);
        if (fromCache != null) {
            return fromCache;
        }
        try {
            PluginRegistryBean registry = MAPPER.reader(PluginRegistryBean.class).readValue(registryUrl.toURL());
            registryCache.put(registryUrl, registry);
            return registry;
        } catch (IOException e) {
            return null;
        }
    }
Loads a plugin registry from its URL.  Will use the value in the
cache if it exists.  If not, it will connect to the remote URL and
grab the registry JSON file.
@param registryUrl the URL of the registry
manager/api/rest-impl/src/main/java/io/apiman/manager/api/rest/impl/PluginResourceImpl.java