We are working on a project to integrate Drools with Apache Hadoop, http://hadoop.apache.org/, and run into some road blocks. We would very much appreciate any suggestions/help from this list. We have an app where we call drools rule engine inside the reducer task of a Hadoop map reduce job. It throws a NullPointerException when we the rule package resource to the knowledge builder. The same code works fine when run as part of a stand alone app. Code: private static Map<String, StatefulKnowledgeSession> sessions = new HashMap<String, StatefulKnowledgeSession>(); private static final String RULE_PACK_DIR = " file:///home/roger/Projects/gridx/ <file:///\\home\pranab\Projects\gridx\>"; private static final String RULE_PACK_EXT = ".drl"; public int process(String rulePackage, String dateTime, String type) throws TException { int rate = 0; StatefulKnowledgeSession session = sessions.get(rulePackage); if (null == session){ KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); String rulePackPath = RULE_PACK_DIR + rulePackage + RULE_PACK_EXT; kbuilder.add( ResourceFactory.newFileResource(rulePackPath ), ResourceType.DRL); if ( kbuilder.hasErrors() ) { System.err.println( kbuilder.getErrors().toString() ); } KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); kbase.addKnowledgePackages(kbuilder.getKnowledgePackages()); session = kbase.newStatefulKnowledgeSession(); sessions.put(rulePackage, session); } ContractRule contractRule = new ContractRule(); contractRule.prepare(dateTime, type);; FactHandle ruleHandle = session.insert(contractRule); session.fireAllRules(); System.out.println("" + contractRule); rate = contractRule.getRate(); session.retract(ruleHandle); return rate; } This line throws the exception: kbuilder.add( ResourceFactory.newFileResource(rulePackPath ), ResourceType.DRL); It works fine as a stand alone app, outside hadoop Roger Smith