I've upgraded OptaPlanner to use the KIE api and I have some feedback :)

What I want to do:
Given of list of DRL's on the classpath, build a KieSession.

Here's how I did it with the new KIE api:

     public KieBase newKieBase(List<String> scoreDrlList) {
            KieServices kieServices = KieServices.Factory.get();
            KieResources kieResources = kieServices.getResources();
            KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
            for (String scoreDrl : scoreDrlList) {
                InputStream scoreDrlIn = getClass().getResourceAsStream(scoreDrl);
                // TODO newClassPathResource() instead, but that breaks (mfusco is looking at it)
                String path = "src/main/resources/optaplanner-kie-namespace/" + scoreDrl;
                kieFileSystem.write(path, kieResources.newInputStreamResource(scoreDrlIn, "UTF-8"));
            }
            KieBuilder kieBuilder = kieServices.newKieBuilder(kieFileSystem);
            kieBuilder.buildAll();
            Results results = kieBuilder.getResults();
            if (results.hasMessages(Message.Level.ERROR)) {
                throw new IllegalStateException("There are errors in the scoreDrl's:\n"
                        + results.toString());
            } else if (results.hasMessages(Message.Level.WARNING)) {
                logger.warn("There are warning in the scoreDrl's:\n"
                        + results.toString());
            }
            KieContainer kieContainer = kieServices.newKieContainer(kieBuilder.getKieModule().getReleaseId());
            KieBase kieBase = kieContainer.getKieBase();
            return kieBase;
     }

     public KieSession newKieSession() {
            ...
            KieSession kieSession = kieBase.newKieSession();
            return kieSession;
     }

Feedback (note: these are suggestions, not demands):

1) To do this, I needed to get acquainted with 9 new concepts:
    KieServices, KieResources, KieFileSystem, KieBuilder, Results, KieModule, KieContainer, KieBase, KieSession.
I only care about 2 of those:
- KieSession
- KieBase (= the factory to build a new KieSession, which I do regularly).
The other 7 concepts probably represent wonderful advanced features which I might want to use later on,
so they should exist,
But in a simple use case like this, I should not have to see them or deal with them.

2) The kie filesystem features leaks into the simple api, even if I don't care about the KieFileSystem at all.
- I should not explicitly need to create a KieFileSystem:
    KieFileSystem kieFileSystem = kieServices.newKieFileSystem();
- Adding certain Resource types fails if you don't specify the fileSystem's path. This fails for example:
    kieFileSystem.write(kieResources.newInputStreamResource(...));
- For the default KieBase to work, the path needs to start with a magical prefix
    String path = "src/main/resources/.../" + ...;

3) To create a KieBase from that kieFileSystem, I need to explicitly do 5+ calls, in the right order:
- call kieServices.newKieBuilder(...)
- call kieBuilder.buildAll()
- call kieBuilder.getKieModule()
- call kieServices.newKieContainer(...)
- call kieContainer.getKieBase()
Some of these have non-obvious parameters.
I'd rather just call:
  kieFileSystem.buildKieBase()

4) I don't like having to write the boilerplate code to check if the are errors:
  if (results.hasMessages(Message.Level.ERROR)) {...}
If there are errors, then kieFileSystem.buildKieBase() should just throw a DroolsRuntimeException.

Solution proposal:

A) Write a facade class that presumes there is only 1 module and the user doesn't need (or want to) to access any of those 7 other concepts.

    public KieBase newKieBase(List<String> scoreDrlList) {
        KieBaseFactory kieBaseFactory = kieServices.newKieBaseFactory();
        for (String scoreDrl : scoreDrlList) {
           kieBaseFactory.addInputStreamResource(scoreDrl, "UTF-8");
        }
        return kieBaseFactory.buildKieBase; // throws exception upon compilation error
    }

Mario's KieHelper is similar, but slightly different.

wkr,
Geoffrey

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