public Resource<Z> decodeSourceFromCache() throws Exception {
        if (!diskCacheStrategy.cacheSource()) {
            return null;
        }

        long startTime = LogTime.getLogTime();
        Resource<T> decoded = loadFromCache(resultKey.getOriginalKey());
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
            logWithTimeAndKey("Decoded source from cache", startTime);
        }
        return transformEncodeAndTranscode(decoded);
    }
Returns a transformed and transcoded resource decoded from source data in the disk cache, or null if no such
resource exists.

@throws Exception
core/src/main/java/com/bumptech/glide/load/engine/DecodeJob.java