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"

    }

    @Override
    public boolean generate(final String thumbnailId, final File outputFile) {
        if (logger.isDebugEnabled()) {
            logger.debug("Generate Thumbnail: {}", thumbnailId);
        }

        if (outputFile.exists()) {
            if (logger.isDebugEnabled()) {
                logger.debug("The thumbnail file exists: {}", outputFile.getAbsolutePath());
            }
            return true;

                    }
                    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";

        }

        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) () -> {

        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        final String thumbnailId = DocumentUtil.getValue(docMap, fessConfig.getIndexFieldId(), String.class);
        final Tuple3<String, String, String> task = new Tuple3<>(getName(), thumbnailId, path);
        if (logger.isDebugEnabled()) {
            logger.debug("Create thumbnail task: {}", task);
        }
        return task;
    }

	<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 -->

					<c:if test="${thumbnailSupport && !empty doc.thumbnail}">
					<div class="mr-3">
						<a class="link d-none d-sm-flex" href="${doc.url_link}" data-uri="${doc.url_link}" data-id="${doc.doc_id}"
							data-order="${s.index}"
						> <img src="${fe:url('/images/blank.png')}" alt="thumbnail"
							data-src="${fe:url('/thumbnail/')}?docId=${f:u(doc.doc_id)}&queryId=${f:u(queryId)}" class="thumbnail"
						>
						</a>
					</div>
					</c:if>

{"index":{"_index":"fess_config.scheduled_job","_id":"thumbnail_generate"}}

/src/main/webapp/WEB-INF/site/
/src/main/webapp/WEB-INF/plugin/*
!/src/main/webapp/WEB-INF/plugin/.keep
/src/main/webapp/WEB-INF/env/crawler/lib/
/src/main/webapp/WEB-INF/env/suggest/lib/
/src/main/webapp/WEB-INF/env/thumbnail/lib/
/src/main/webapp/WEB-INF/thumbnails/
/src/main/webapp/jar/
/dbflute_fess/extlib/*
/dbflute_fess/log/*.log
/dbflute_h2/log/*.log
/dbflute_mysql/log/*.log
/dbflute_oracle/log/*.log
/src/main/webapp/WEB-INF/conf/*.properties