从单独的 maven 项目中的另一个 drl 文件引用 function

Question

I have multiple maven projects with DROOLs drl files in them. I would like to put things like helper functions in a central location and then have the drls in other projects be able to use them, but it isn't working.

The common project is a maven dependency in the other projects. I can prove this is working because I have access to the facts that I define in the common project, but I don't have access to functions.

1. I initially tried creating a file called: helperfunctions.drl and put the functions directly in the file thinking they would be available without any imports when building and they are not found.

2. I then tried wrapping the functions in a declare HelperFunctions end, but this syntax doesn't work.

3. Finally, I tried changing the file to HelperFunctions.java and did public class HelperFunctions and made all of the methods static. Then in the other project drls I imported using the namespace com.myproject.common.

I am out of options, is there anything else I can try or is this not possible?

Answer 1

I'm a little unclear about what you've attempted, but Java code from a dependency (your point #3) can be invoked from the rules if you have the Jar on your classpath.

Imagine you have your project set up as follows:

|-rule-utils (project name)
|-- src\main\java\com\mycompany\common\HelperFunctions.java
|--pom.xml

And you have defined some utility function public static void doSomethingUseful() in your HelperFunctions class.

In your other project where your rules exist, you can include your project1 jar as a dependency, possibly as follows in your pom:

<dependency>
  <artifactId>rule-utils</artifactId>
  <groupId>com.mycompany</groupId>
</dependency>

And then you can import and use HelperFunctions and its doSomethingUseful method as you would any other Java code in your drl:

import com.mycompany.common.HelperFunctions;

rule "Example rule"
when
then
  HelperFunctions.doSomethingUseful();
end

In my experience, it's pretty common to invoke third-party utility code this way, for example the Apache commons' utility classes like StringUtils and CollectionUtils (though more often on the left hand side than in the consequences.)