append(b, "count", () -> c.getCollectionCount()).append(',');
            append(b, "time", () -> c.getCollectionTime().getMillis()).append('}');
            return b.toString();
        }).collect(Collectors.joining(",")));
        buf.append("},");
        final Threads threads = jvmStats.getThreads();
        buf.append("\"threads\":{");
        append(buf, "count", () -> threads.getCount()).append(',');

    private long expiry = 30 * 24 * 60 * 60 * 1000L;

    public String execute() {
        try {
            final long count = ComponentUtil.getThumbnailManager().purge(getExpiry());
            return "Deleted " + count + " thumbnail files.";
        } catch (final Exception e) {
            logger.error("Failed to purge thumbnails.", e);
            return e.getMessage();
        }
    }