[rules-users] How to use Drools's global object in a *.java file?

[Wolfgang Laun]

It may not be a good idea to use a wrapper class from java.lang for
collecting results from rule execution. Setting and retrieving a
global is simple, as suggested by Frank and Esteban:

Double d1 = new java.lang.Double(0);
ksession.setGlobal("result", d1 );
// execute the session
Double d2 = (Double)ksession.setGlobal("result" );

But how do you add something to your result? You might think that this is it:
rule "not a good idea"
when
    ... $x ...
then
      result += $x;
end

But this isn't going to work, because the Double is made available as a
local copy. To update the global, you'll have to use something like

   kcontext.getKnowledgeRuntime().setGlobal( "result", result+$x );

It would be better to write a simple class, call it Sum, with a field
double value and a getter and a setter, and then you can do

Sum s = new Sum();
ksession.setGlobal("result", s );
// execute the session
double result = s.getValue(); // the reference is still good

And the rule uses

   then
      result.setValue( result.getValue() + $x );
   end

or add a convenience method plus(double d) to Sum
  then
      result.plus( $x );
   end

-W



On 15/01/2013, Esteban Aliverti <esteban.aliverti at gmail.com> wrote:
> After you fireAllRules() you can get latest value of the global using:
> Double result = (Double) ksession.getGlobal("result");
>
> Best Regards,
>
>
> XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
>
> Esteban Aliverti
> - Blog @ http://ilesteban.wordpress.com
>
>
> On Tue, Jan 15, 2013 at 10:20 AM, FrankVhh
> <frank.vanhoenshoven at agserv.eu>wrote:
>
>> java.lang.Double result = new java.lang.Double(0);
>> ksession.setGlobal("result", result);
>>
>> ?
>>
>>
>> penny wrote
>> > test.java file:
>> >
>> > KnowledgeBase kbase = readKnowledgeBase();
>> > StatefulKnowledgeSession ksession =
>> > kbase.newStatefulKnowledgeSession();
>> > ksession.setGlobal("result", new java.lang.Double(0));
>> >
>> >
>> > I have used the global variable “result” in the rule file,how to use it
>> in
>> > the test.java file?
>> > I need a judgement like “if(result>0)”.
>>
>>
>>
>>
>>
>> --
>> View this message in context:
>> http://drools.46999.n3.nabble.com/How-to-use-Drools-s-global-object-in-a-java-file-tp4021532p4021535.html
>> Sent from the Drools: User forum mailing list archive at Nabble.com.
>>
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>