static String toString(Object holder, HttpVfs vfs, Clock clock,
                           @Nullable String entryCacheSpec, int maxCacheEntrySizeBytes,
                           boolean serveCompressedFiles, boolean autoIndex,
                           @Nullable Iterable<Entry<AsciiString, String>> headers,
                           MediaTypeResolver mediaTypeResolver, @Nullable List<String> fallbackFileExtensions) {

        return MoreObjects.toStringHelper(holder).omitNullValues()
                          .add("vfs", vfs)
                          .add("clock", clock)
                          .add("entryCacheSpec", entryCacheSpec)
                          .add("maxCacheEntrySizeBytes", maxCacheEntrySizeBytes)
                          .add("serveCompressedFiles", serveCompressedFiles)
                          .add("autoIndex", autoIndex)
                          .add("headers", headers)
                          .add("mediaTypeResolver", mediaTypeResolver)
                          .add("fallbackFileExtensions", fallbackFileExtensions)
                          .toString();
    }
Returns the file extensions that are appended to the file name when the file is not found.
core/src/main/java/com/linecorp/armeria/server/file/FileServiceConfig.java