code: public void uploadFiles(
          String[] fieldNames,
          final I_CmsJavaScriptObjectCallback fileCallback,
          I_CmsErrorCallback errorCallback) {
  
          Set<String> fieldSet = new HashSet<String>();
          for (String field : fieldNames) {
              fieldSet.add(field);
          }
  
          m_formWrapper.uploadFields(fieldSet, new Function<Map<String, String>, Void>() {
  
              public Void apply(Map<String, String> input) {
  
                  fileCallback.call(CmsJsUtils.convertMapToJsObject(input));
                  return null;
              }
          }, errorCallback);
      }
docs: Uploads multiple files.<p>
  
  @param fieldNames the array of form field names containing files to upload
  @param fileCallback the callback for the results
  @param errorCallback the error handling callback