code: public FileItem createItem(String fieldName, String contentType, boolean isFormField, String fileName) {
          return new MemoryFileItem(fieldName, contentType, isFormField, fileName, sizeThreshold);
      }
docs: Create a new {@link MemoryFileItem} instance from the supplied parameters
  and the local factory configuration.
  
  @param fieldName the name of the form field
  @param contentType the content type of the form field
  @param isFormField {@code true} if this is a plain form field; {@code false} otherwise
  @param fileName the name of the uploaded file, if any, as supplied by the browser or other client
  @return the newly created file item