How to call a Java function in drools?

Question

I want to call a Java function from a Utils class which calls a JPA Repository method for retrieving a custom object.

I want to call this function from a Drools decision table. Now, this simple function is giving Null Pointer Exception and I have already lost several hours on this.

I have a Functions field declared under "Import" section of the decision table, and there I have declared a simple function which calls this particular Java function with the repository method.

Can you provide me with a solution?

Answer 1

Here is an example of calling java method from drools. setLocalTax() method is available from ItemCity class. Using the '$item' object we can invoke.

package droolsexample

// list any import classes here.
import com.sample.ItemCity;
import java.math.BigDecimal;

// declare any global variables here
dialect "java"
rule "Pune Medicine Item"

   when
      $item : ItemCity (purchaseCity == ItemCity.City.PUNE,
                       typeofItem == ItemCity.Type.MEDICINES)

   then
      BigDecimal tax = new BigDecimal(0.0);
      $item.setLocalTax(tax.multiply($item.getSellPrice()));
end