[rules-users] Problem in using genrics with drools4.0.1.

[Mark Proctor]

Drools, and probably the underlying MVEL that the 'from' uses, has no 
understanding of Generics, so I expect thats your problem.

Mark
Gaurav2007 wrote:
> HI ALL,
>
> I am using drool 4.0.1 in my project.
> I am facing problem in using generics feature of jdk1.5.
>
> My objective is to perform validation on the basis of data type of variable.
> for storing values of variable i have one Attribute Class it contains getter
> setter for values of attribute and attributeId which is a string but value
> of attribute is of deferent type so i am thinking to use generics here.
>
> public class Attribute<T> {
>     
>     public String qualifiedName;
>
>     public T newValue;
>
>     public T oldValue;
>
>     public String getQualifiedName() {
>         return qualifiedName;
>     }
>
>     public void setQualifiedName(String qualifiedName) {
>         this.qualifiedName = qualifiedName;
>     }
>
>     public T getNewValue() {
>         return (T)newValue;
>     }
>
>     public void setNewValue(T newValue) {
>         this.newValue = newValue;
>     }
>
>     public T getOldValue() {
>         return oldValue;
>     }
>
>     public void setOldValue(T oldValue) {
>         this.oldValue = oldValue;
>     }
> }
>
>
> my rule for date comparison looks like:
>
> //Date Comparison.
> rule "W250.1 DateComparison"
> 	when
> 		$dto : DataProvider()
> 	Attribute(newValue < "29-Oct-2007") from $dto.getValue("W250.1")
> 	then
> 		System.out.println ("Error in Date check \t");
> end
>
> DataProvider class it is responsible to give instance of attribute
> corresponding to attributeId:
>
> public class DataProvider {
>     
>     HashMap<String,Attribute> fieldMap=new HashMap<String, Attribute>();
>     
>     public DataProvider() {
>         populateMap();
>     }
>     
>     public Attribute  getValue(String qualifiedName){
>             Attribute attribute = fieldMap.get(qualifiedName);
>             return attribute;
>     }
>     
>     public void populateMap(){
>         Attribute<Date> attribute = new Attribute<Date>();
>         SimpleDateFormat format = new SimpleDateFormat("dd-MMM-yyyy");
>            Date date;
>         try {
>             date = format.parse("27-Oct-2007");
>             attribute.setQualifiedName("W250.1");
>             attribute.setOldValue(date);
>             attribute.setNewValue(date);
>             fieldMap.put(attribute.getQualifiedName(),attribute);
>             
>         }
>         catch (ParseException e) {
>             e.printStackTrace();
>         }
>
>     }
> }
>
> in this case i am getting exception:
> Exception in thread "main" java.lang.ClassCastException: java.lang.String
>
> when i am not using generics this rule is working fine.
> but in this case how should i perform validation depending upon data type of
> attribute.
>
> can you please help me in solving this problem.
>
> Thanks,
> Gaurav Joshi
>
>