public class MyAction extends ActionSupport implements ParameterNameAware {

   /**
    * This method will filter out parameters that
    * start with "d-" followed by a numeric digit,
    *  because parameters of this form are generated by displayTag, 
    *  and are treated by webwork as an invalid OGNL expressions causing
    * webwork to throw an ognl.InappropriateExpressionException exception.  
    * Note that the exception is only thrown when webwork is set in devmode.  
    * However, to prevent this error, the ParameterNameAware interface has been
    * implemented which requires this method.
    * This method could be implemented more simply using java's regular expression 
    * support, but such an implementation may suffer from readability except for
    * people who are very strong in understanding java's RegEX semantics.
    */
    public boolean acceptableParameterName(String parameterName){
      boolean retVal = true;
      if(parameterName!=null && parameterName.startsWith("d-") )
		 if( parameterName.length()>2) {
			String thirdCharacter = parameterName.substring(2,3);
			if(StringUtils.isNumeric(thirdCharacter)){
				retVal = false;
			}
		}
      return retVal;
    }
 }