What is the new accepted way of programmatically creating new drools rules in Drools 6?

Question

In short I want to create, edit and delete rules from a rules repository at runtime. I'm having trouble figuring out how to do this in drools 6+.

I know in a previous version of drools (<= 5.6), that there was an XML representation of a .drl file and an API for working with it: https://docs.jboss.org/drools/release/5.6.0.Final/drools-expert-docs/html/ch04.html#d0e8052.

The drools documentation as of 5.6 indicates this deprecated and it appears to be completely removed at 6. I don't want to use an API that is already known to have no direct upgrade path.

Exposing the Guvnor or Workbench UIs to users for rules editing is also not a good fit here due to workflow requirements and due to the complexity of the web user interfaces. I want to create and manage the rules from Java code.

I want a better method than string templating to a .drl file for creating new rules and modifying rules. What exists for programmatically creating new rules from Java? I have done a lot of searching but can't seem to find a set of Java API calls for this.

Answer 1

I don't know if this is the 'accepted' way, but with the following code I comine .drl files with programmatically created rules in Drools 6.

public KieContainer build(KieServices kieServices) {
    KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
    ReleaseId rid = kieServices.newReleaseId("com.example.rulesengine", 
        "model-test", "1.0-SNAPSHOT");
    kieFileSystem.generateAndWritePomXML(rid);

    kieFileSystem.write("src/main/resources/rules.drl", 
        getResource(kieServices, "rules.drl"));

    addRule(kieFileSystem);

    KieBuilder kieBuilder = kieServices.newKieBuilder(kieFileSystem);
    kieBuilder.buildAll();
    if (kieBuilder.getResults().hasMessages(Message.Level.ERROR)) {
        throw new RuntimeException("Build Errors:\n" + 
           kieBuilder.getResults().toString());
    }

    return kieServices.newKieContainer(rid);
}

private void addRule(KieFileSystem kieFileSystem) {
    PackageDescrBuilder packageDescrBuilder = DescrFactory.newPackage();
    packageDescrBuilder
            .name("com.example.model")
            .newRule()
            .name("Is of valid age")
            .lhs()
            .pattern("Person").constraint("age < 18").end()
            .pattern().id("$a", false).type("Action").end()
            .end()
            .rhs("$a.showBanner( false );")
            .end();

    String rules = new DrlDumper().dump(packageDescrBuilder.getDescr());
    kieFileSystem.write("src/main/resources/rule-1.drl", rules);
}

private Resource getResource(KieServices kieServices, String resourcePath) {
    try {
        InputStream is = Resources.getResource(resourcePath).openStream(); //guava
        return kieServices.getResources()
                  .newInputStreamResource(is)
                  .setResourceType(ResourceType.DRL);
    } catch (IOException e) {
        throw new RuntimeException("Failed to load drools resource file.", e);
    }
}

I use the Guava Resources class.