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You should probably start by separating your concerns into small, extensible pieces that can be easily stitched together and replaced.

interface Transform {
    Widget widget(LookupData lookupData);
}

That by itself is a piece

interface Source {
   LookupData lookupData();
}

There's your read side effect.

class WidgetMaker {
    Source source;
    Transform transform;

    Widget widget() {
        return transform.widget(source.lookupData());
    }
}

There's your composition.

class Cache implements Source {
    LookupData cache = null;          
    Source upstream;

    LookupData lookupData() {
        if (null == cache) {
            cache = upstream.lookupData();
        }
        return cache;
    }
}

Now you can put a mini cache in front of any source

... and so on.