code: public void substringField(String sourceField, String targetField, String from, String to) {
          TransformationStep step = new TransformationStep();
          step.setTargetField(targetField);
          step.setSourceFields(sourceField);
          step.setOperationParameter(TransformationConstants.SUBSTRING_FROM_PARAM, from);
          step.setOperationParameter(TransformationConstants.SUBSTRING_TO_PARAM, to);
          step.setOperationName("substring");
          steps.add(step);
      }
docs: Adds a substring step to the transformation description. The value of the source field is taken and it is tried
  to build the substring from the given index from to the given index to. From and to must be Integers written as
  String, the value of the source field must also be a String.