With Drools 6.x how do I avoid Maven and the Compiler?

Question

I'm looking into providing a 'hot-swap' capability for switching between different versions of sets of drools rules. The target deployment is in WebSphere, and the rules will all be run in stateless session beans. Ideally I want to pre-compile and package the rules into some discrete file and get the Application Server to determine that new rules are available, and load them (skipping the compilation step).

The Drools documentation indicates this should be possible - but is splendidly vague on the mechanics. The details on the Java EE side are not an issue but the pre-compilation is providing an headache.

Following some posts I've pulled together some logic which I thought would do the trick - the following compiles a rules file and serializes it out to disk:

private void process(String outputFile, String inputFile) throws Exception {
    String drl = fileToString(inputFile);
    KieServices ks = KieServices.Factory.get();
    KieFileSystem kfs = ks.newKieFileSystem().write( "src/main/resources/r1.drl", drl );
    ks.newKieBuilder( kfs ).buildAll();
    ReleaseId releaseId = ks.getRepository().getDefaultReleaseId();
    InternalKieModule kieModule = (InternalKieModule) ks.getRepository().getKieModule( releaseId );
    byte[] jar = kieModule.getBytes();
    serialize(jar, outputFile);
    System.out.println("Class of InternalKieModule is " + kieModule.getClass());
}

The following reads it back ready to create a KieSession:

private KieContainer getKbase(KieServices ks) throws Exception {
    byte[] jar = deserialize(RULES_SER);
    Resource jarRes = ks.getResources().newByteArrayResource(jar);
    KieModule km = ks.getRepository().addKieModule(jarRes);
    releaseId = km.getReleaseId();
    KieContainer kc = ks.newKieContainer(km.getReleaseId());
    return kc;
}

Works fine BUT ... I was horrified to discover I seem to need everything but the kitchen sink to actually run it - just under 50 separate jar files - taking up 16 MB and including the Ant jar, 10 Maven jars, and the drools compiler jar even though I'm not supposed to be compiling anything, and I'm certainly not trying to use Maven or Ant! Of the 67 Jar files in the distribution nearly all seem directly linked to Maven, and very few (I'd judge from the approach below about 10 to 15) actually have anything to do with a rules runtime.

Going back to an example I built with Drools 5, several years back, I came up with the following code to reload a drl file I'd compiled separately using the Knowledge Base APIs:

private KnowledgeBase readSavedKnowledgeBase() throws Exception {
    byte[] serializedKb = (byte[]) deserialize(RULES_SER);
    ByteArrayInputStream bais = new ByteArrayInputStream(serializedKb);
    DroolsObjectInputStream ois = new DroolsObjectInputStream(bais);
    KnowledgeBase kbase = (KnowledgeBase) ois.readObject();
    ois.close();
    return kbase;
}

This works fine with 6.1. I only need 9 jars, (and I don't need the compiler jar) - and my run-time is a fairly reasonable 5MB. The down side is that Eclipse is unhappy since the KnowledgeBase class is now deprecated.

Could someone point the way to allowing me to get the same result using non-deprecated classes but without all the baggage of Maven and so on which I don't want or need to actually run some rules?

laune · Accepted Answer · 2014-12-15T18:44:25.137

Some 6.x code for building:

    KieServices ks = KieServices.Factory.get();
    KieFileSystem kfs = ks.newKieFileSystem();
    FileInputStream fis = new FileInputStream( "sale/sale.drl" );
    kfs.write( "src/main/resources/sale.drl",
                   ks.getResources().newInputStreamResource( fis ) );
    KieBuilder kieBuilder = ks.newKieBuilder( kfs ).buildAll();
    Results results = kieBuilder.getResults();
    if( results.hasMessages( Message.Level.ERROR ) ){
        System.out.println( results.getMessages() );
        throw new IllegalStateException( "### errors ###" );
    }
    KieContainer kieContainer =
        ks.newKieContainer( ks.getRepository().getDefaultReleaseId() );

    // CEP - get the KIE related configuration container and set the EventProcessing (from default cloud) to Stream
    KieBaseConfiguration config = ks.newKieBaseConfiguration();
    config.setOption( EventProcessingOption.STREAM );
    KieBase kieBase = kieContainer.newKieBase( config );
    //      KieSession kieSession = kieContainer.newKieSession();
    KieSession kieSession = kieBase.newKieSession();

You can serialize out the KieBase and back in for fast startup. I run this for various tests using the below CLASSPATH, but for execution you'll not need antlr, decisiontables, templates, and (maybe) others.

export CLASSPATH=".:$root/drools-core-${tag}.jar:$root/kie-api-${tag}.jar:$roo/kie-internal-${tag}.jar:$root/knowledge-internal-api-${tag}.jar:$root/drools-compiler-${tag}.jar:$root/antlr-runtime-3.5.jar:$root/ecj-4.3.1.jar:$root/mvel2-2.1.9.Final.jar:$root/drools-decisiontables-${tag}.jar:$root/drools-templates-${tag}.jar:$root/protobuf-java-2.5.0.jar:$root/slf4j-api-1.7.2.jar:$root/xstream-1.4.7.jar:$SLF4J"

For serialiazation and its counterpart use the usual mantra:

ObjectOutputStream out =
        new ObjectOutputStream( new FileOutputStream( pkgPath ) );
out.writeObject( kieBase );
out.close();
//---------- In another program ---------------
ObjectInputStream in =
       new ObjectInputStream( new FileInputStream( pkgPath ) );
@SuppressWarnings( "unchecked" )
KieBase kieBase = (KieBase)in.readObject();
in.close();

laune, thanks for quick response, but my issue is if I try to run your code I have to put the compiler on the classpath - which drags in all the Maven, and Ant stuff.What I need to understand is HOW to serialize out the KieBase, in such a manner that I can read it back in to create a session without getting all extra stuff in at run-time. — Bob Moore, Dec 15 '14 at 17:10
Did you separate this into two runs: one with compile and serialization and another one with deserialization and execution? Serialiiation is a standard Java thing, nothing Drool-ish - is that your problem? — laune, Dec 15 '14 at 18:36
laune - thank you very much - your code fragment shows me where I was going wrong. The earlier example I worked from was just serialising the wrong object. Once I serialised the kiebase rather than the kiemodule, I was able to trim down to a nice minimal runtime 5MB and only 6 jars instead of 48 — Bob Moore, Dec 16 '14 at 08:26

score 0 · Answer 2 · answered Dec 22 '14 at 21:37

It only brings in Maven if you have kie-ci on the classpath, remove that and you will not have any maven. However you will also not have any dependency management or pom analysis - if you don't need those things, you don't need maven to compile. Without kie-ci it will fall back to a "light" pom.xml parser. You can still programmatically provide it the other kiemodulies it depends on.

With Drools 6.x how do I avoid Maven and the Compiler?

2 Answers2

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