Chapter 19. Hello World Example

19.1. HelloWorld Example: Creating the KnowledgeBase and Session

final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();

// this will parse and compile in one step
kbuilder.add(ResourceFactory.newClassPathResource("HelloWorld.drl",
        HelloWorldExample.class), ResourceType.DRL);

// Check the builder for errors
if (kbuilder.hasErrors()) {
    System.out.println(kbuilder.getErrors().toString());
    throw new RuntimeException("Unable to compile \"HelloWorld.drl\".");
}

// get the compiled packages (which are serializable)
final Collection<KnowledgePackage> pkgs = kbuilder.getKnowledgePackages();

// add the packages to a KnowledgeBase (deploy the knowledge packages).
final KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
kbase.addKnowledgePackages(pkgs);

final StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
  • A KnowledgeBuilder is used to turn a DRL source file into Package objects which the Knowledge Base can consume.
  • The add method takes a Resource interface and a Resource Type as parameters. The Resource can be used to retrieve a DRL source file from various locations; in this case the DRL file is being retrieved from the classpath using a ResourceFactory, but it could come from a disk file or a URL.
  • Multiple packages of different namespaces can be added to the same Knowledge Base.
  • While the Knowledge Base will validate the package, it will only have access to the error information as a String, so if you wish to debug the error information you should do it on the KnowledgeBuilder instance.
  • Once the builder is error free, get the Package collection, instantiate a KnowledgeBase from the KnowledgeBaseFactory and add the package collection.
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