check_command convert
  check_command pdftoppm
  check_command unoconv
  tmp_pdf_file=/tmp/thumbnail.$$.pdf
  unoconv -e PageRange=1-1 -o ${tmp_pdf_file} -f pdf "${target_file}"
  if [[ ! -f ${tmp_pdf_file} ]] ; then
    echo "unoconv does not work."
    exit 1
  fi
  tmp_png_prefix=/tmp/thumbnail.png.$$
  pdftoppm -png -singlefile ${tmp_pdf_file} ${tmp_png_prefix}
  tmp_png_file="${tmp_png_prefix}.png"

        final String commandTimeoutStr = fessConfig.getSystemProperty("thumbnail.command.timeout");
        if (commandTimeoutStr != null) {
            commandTimeout = Long.parseLong(commandTimeoutStr);
        }
        final String commandDestroyTimeoutStr = fessConfig.getSystemProperty("thumbnail.command.destroy.timeout");
        if (commandDestroyTimeoutStr != null) {

                    }
                    break;
                default:
                    logger.error("Unknown thumbnail result: {} -> {}", thumbnailId, responseData.getUrl());
                    break;
                }
            } catch (final Throwable t) {

        String imagePath = "thumbnail/600x400.png";
        try (ImageInputStream input = ImageIO.createImageInputStream(classLoader.getResourceAsStream(imagePath))) {
            generator.saveImage(input, outputFile);
        }
        assertImageSize(outputFile, 100, 66);

        imagePath = "thumbnail/600x400.gif";

	<property name="crawler.dir" value="${basedir}/src/main/webapp/WEB-INF/env/crawler" />
	<property name="suggest.dir" value="${basedir}/src/main/webapp/WEB-INF/env/suggest" />
	<property name="thumbnail.dir" value="${basedir}/src/main/webapp/WEB-INF/env/thumbnail" />
	<property name="site.dir" value="${basedir}/src/main/webapp/WEB-INF/site" />
	<property name="kopf.branch" value="fess-14" />

	<!-- Maven Repository -->

        }

        if (logger.isDebugEnabled()) {
            logger.debug("Thumbnail Directory: {}", baseDir.getAbsolutePath());
        }

        thumbnailTaskQueue = new LinkedBlockingQueue<>(thumbnailTaskQueueSize);
        generating = !Constants.TRUE.equalsIgnoreCase(System.getProperty("fess.thumbnail.process"));
        thumbnailQueueThread = new Thread((Runnable) () -> {

                                "Failed to process a thumbnail content: " + url + " (Response URL is empty)");
                    }
                    return consumer.test(responseData);
                } catch (final CrawlingAccessException e) {
                    if (logger.isDebugEnabled()) {
                        throw new ThumbnailGenerationException("Failed to process a thumbnail content: " + url, e);
                    }

searchlog.request.headers=
searchlog.process.batch_size=100

thumbnail.html.image.min.width=100
thumbnail.html.image.min.height=100
thumbnail.html.image.max.aspect.ratio=3.0
thumbnail.html.image.thumbnail.width=100
thumbnail.html.image.thumbnail.height=100
thumbnail.html.image.format=png
thumbnail.html.image.xpath=//IMG
thumbnail.html.image.exclude.extensions=svg,html,css,js
thumbnail.generator.interval=0
thumbnail.generator.targets=all

<a href="fess-theme-simple/" title="fess-theme-simple/">fess-theme-simple/</a>                                               -         -      
<a href="fess-thumbnail-playwright/" title="fess-thumbnail-playwright/">fess-thumbnail-playwright/</a>                                       -         -      

            throw responseManager.new404("Thumbnail for " + form.docId + " is not found.");
        }

        final File thumbnailFile = thumbnailManager.getThumbnailFile(doc);
        if (thumbnailFile == null) {
            if (fessConfig.isThumbnailEnabled()) {
                thumbnailManager.offer(doc);
            }
            // 404
            throw responseManager.new404("Thumbnail for " + form.docId + " is under generating.");