Java code:

    private Object singleValueFromString(ReportDefinitionParam rdp, String s) {
       if (rdp?.isTypeDateTime()) {
           try { 
               return new DateTime(Date.parse(rdp.pattern ?: 'MM/dd/yyyy HH:mm', s)) 
           } catch (Exception e) { 
               try { 
                   // try date portion only
                   return new DateTime(Date.parse(rdp.pattern ?: 'MM/dd/yyyy', s)) 
               } catch (Exception e2) { return null }
           }
        } else if (rdp?.isTypeDate()) {
            try { return Date.parse(rdp.pattern ?: 'MM/dd/yyyy', s) } catch (Exception e) { return null }
        } else if (rdp?.isTypeInteger()) {
            try { return new BigDecimal(s) as Integer } catch (Exception e) { return null }
        } else if (rdp?.isTypeDecimal()) {
            try { return new BigDecimal(s) } catch (Exception e) { return null }
        } else {
            return s
        }
    }