Question

The situation is easy. I created a rules file:

package org.domain.rules;
dialect "mvel"
import eu.ohim.fsp.core.configuration.domain.xsd.Section;

global java.lang.String sectionName;

rule "rule 1"
salience 1000
when
    Section($name : nameOfTheSection)
    eval(sectionName == null)
then
    System.out.println("Section: " + $name+ "("+$name.length()+")");
    System.out.println("Section Name: " + sectionName + "("+sectionName.length()+")");
    System.out.println("Mark Details: " + sectionName.equals(null));
end

And before firing the rules I added the Section object with a valid coreName and the globals:

public void fireInserted(Section section1) {
    kstateful.insert(section1);
    kstateful.setGlobal("sectionName", new String("markudetails"));
    kstateful.fireAllRules();
}

The result is:

Section: markudetails(12)
Section Name: markudetails(12)
Mark Details: false

QUESTION: How can it be possible? in when part is null and in then part is not null!!!

Answer 1

Global vars are not a part of the knowledge base, but a separate channel to push some context into the rule execution. It is not appropriate to use them in a when clause. The exact reason why it was null in your case may be hard to trace, since rule activation is completely decoupled from rule execution. The variable may simply not be bound at when clause evaluation time, but is bound at then clause execution time.

To summarize: don’t use globals in a when clause, that’s not what they are for.

Your problem has an easy general solution: you can insert a configuration object into the knowledge. That object can have your desired “sectionName” property which you will then find easy to test in a when.

As an aside, it is meaningless to test for object.equals(null) — this can never produce true. There is also no need to use new String("markudetails"). Instead use just "markudetails".