public FileService build() {
        if (autoDecompress && !serveCompressedFiles) {
            throw new IllegalStateException("Should enable serveCompressedFiles when autoDecompress is set");
        }

        return new FileService(new FileServiceConfig(
                vfs, clock, entryCacheSpec, maxCacheEntrySizeBytes,
                serveCompressedFiles, autoDecompress, autoIndex, buildHeaders(),
                mediaTypeResolver.orElse(MediaTypeResolver.ofDefault()), fallbackFileExtensions()));
    }
Returns a newly-created {@link FileService} based on the properties of this builder.
core/src/main/java/com/linecorp/armeria/server/file/FileServiceBuilder.java