code: public void lengthField(String sourceField, String targetField, String function) {
          TransformationStep step = new TransformationStep();
          step.setSourceFields(sourceField);
          step.setTargetField(targetField);
          step.setOperationParameter(TransformationConstants.LENGTH_FUNCTION_PARAM, function);
          step.setOperationName("length");
          steps.add(step);
      }
docs: Adds a length step to the transformation description. The step takes the object from the source field and
  calculate the length through the given method function (which needs to be implemented by the object). The result
  will be written in the target field. If the function is null, then "length" will be taken as standard function.