componentsByTag.java

private <T> void populateComponentsByTag(
        Map<String, ArrayList<String>> componentsByTag,
        Map<String, T> components
) {
    // Type T can be either Bolt or SpoutSpec, so that this logic can be reused for both component types
    JSONParser parser = new JSONParser();

    for (Entry<String, T> componentEntry : components.entrySet()) {
        JSONObject conf = null;

        String componentID = componentEntry.getKey();
        T component = componentEntry.getValue();

        try {
            // Get the component's conf irrespective of its type (via java reflection)
            Method getCommonComponentMethod = component.getClass().getMethod("get_common");
            ComponentCommon commonComponent = (ComponentCommon) getCommonComponentMethod.invoke(component);
            conf = (JSONObject) parser.parse(commonComponent.get_json_conf());
        } catch (ParseException | NoSuchMethodException | IllegalAccessException | InvocationTargetException ex) {
            ex.printStackTrace();
        }

        String tags;

        // If there's no config, use a fake tag to group all untagged components
        if (conf == null) {
            tags = "untagged";
        } else {
            tags = (String) conf.get("tags");

            // If there are no tags, use a fake tag to group all untagged components
            if (tags == null) {
                tags = "untagged";
            }
        }

        // If the component has tags attached to it, handle it by populating the componentsByTag map.
        // Loop through each of the tags to handle individually
        for (String tag : tags.split(",")) {
            tag = tag.trim();

            if (componentsByTag.containsKey(tag)) {
                // If we've already seen this tag, then just add the component to the existing ArrayList.
                componentsByTag.get(tag).add(componentID);
            } else {
                // If this tag is new, then create a new ArrayList,
                // add the current component, and populate the map's tag entry with it.
                ArrayList<String> newComponentList = new ArrayList<String>();
                newComponentList.add(componentID);
                componentsByTag.put(tag, newComponentList);
            }
        }
    }
}