@POST
 @Path("createPdf")
 public Response createPdf(String htmlTemplateParam, String json) {

 //Read template from endpoint param or start off with reading local html template from resource folder
String templateHtml = IOUtils.toString(getClass().getResourceAsStream(HTMLTemplateFiles.INCOMING_TEMPLATE));

RequestJson requestJson = [Prepare json before passing to HTML Template]];

if(requestJson.isContentValid()) {

    LOG.info("incoming data successfully validated");

    // TODO
    // Pass the requestJson (Endpoint Param JSON ) to templateHtml
    // Trigger the reading of the Json data and populating different HTML DOM elements using some sort of expression predifined in HTML

    // Get hold of the rendered HTML
    String resolvedHtml = [HTML with data from json param into endpoint];

    // The next bit is done
    String pdf = htmlToPdfaHandler.generatePdfFromHtml(resolvedHtml);

    javax.ws.rs.core.Response response = Response.ok().entity(Base64.decodeBase64(pdf)).build();
            }
}

Configuration cfg = new Configuration(new Version("2.3.23"));
    cfg.setDefaultEncoding("UTF-8");

    // Loading you HTML template (via file or input stream):
    Template template = cfg.getTemplate("template.html");

    // You need convert json to map of parameters (key-value):
    Map<String, Object> templateData = new HashMap<>();
    templateData.put("msg", "Today is a beautiful day");

    try (StringWriter out = new StringWriter()) {
        // In output stream the result will be template with values from map:
        template.process(templateData, out);
        System.out.println(out.getBuffer().toString());

        out.flush();
    }