@Override
            public File getCacheDirectory() {
                File cacheDirectory = context.getExternalCacheDir();
                if (cacheDirectory == null) {
                    return null;
                }
                if (diskCacheName != null) {
                    return new File(cacheDirectory, diskCacheName);
                }
                return cacheDirectory;
            }
Creates an {@link com.bumptech.glide.disklrucache.DiskLruCache} based disk cache in the external disk cache
directory.
<p/>
<b>Images can be read by everyone when using external disk cache.</b>
core/src/main/java/com/bumptech/glide/load/engine/cache/ExternalCacheDiskCacheFactory.java