There is probably something wrong with your drl.

Try starting from an empty drl file and then add each of the rules and definitions in it one by one until you find the one causing problems. Then you can produce a test case and create a JIRA issue for it if it doesn’t already exist – as it should at least be giving a useful error message and not throwing a null pointer exception.

Thomas

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Roger Smith
Sent: 09 November 2010 06:41
To: rules-users@lists.jboss.org
Subject: [rules-users] NullPointerException when using Drools rule template

All -

I tried out Drools rule template with a with a proptotype app. Drools is throwing NullPointerException as below. I would much appreciate if someone on this list can help.

java.lang.NullPointerException
    at org.drools.template.parser.DefaultTemplateColumn.createCellCondition(DefaultTemplateColumn.java:68)
    at org.drools.template.parser.DefaultTemplateColumn.addCondition(DefaultTemplateColumn.java:91)
    at org.drools.template.parser.DefaultTemplateRuleBase.createColumnConditions(DefaultTemplateRuleBase.java:105)
    at org.drools.template.parser.DefaultTemplateRuleBase.createTemplateRule(DefaultTemplateRuleBase.java:98)
    at org.drools.template.parser.DefaultTemplateRuleBase.getDTRules(DefaultTemplateRuleBase.java:85)
    at org.drools.template.parser.DefaultTemplateRuleBase.<init>(DefaultTemplateRuleBase.java:64)
    at org.drools.template.parser.TemplateDataListener.<init>(TemplateDataListener.java:76)
    at org.drools.template.parser.TemplateDataListener.<init>(TemplateDataListener.java:52)
    at org.drools.template.ObjectDataCompiler.compile(ObjectDataCompiler.java:44)

Here is my code

        KnowledgeBuilder kBuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
        ObjectDataCompiler converter = new ObjectDataCompiler();
        InputStream dis = new FileInputStream( new File( "/home/pranab/Projects/gridx/ct11_1.drl" ) );
        if (null == dis){
          System.out.println("null rule template stream");
          return;
        }

        Collection<Map<String,Object>> paramMaps = new ArrayList<Map<String,Object>>();

        Map<String,Object> params = new HashMap<String,Object>();

        params.put("summerOnPeakPrimaryRate", new Integer(299));
        params.put("summerOnPeakSecondaryRate", new Integer(524));
        params.put("summerSemiPeakPrimaryRate", new Integer(176));
        params.put("summerSemiPeakSecondaryRate", new Integer(305));
        params.put("summerOffPeakPrimaryRate", new Integer(139));
        params.put("summerOffPeakSecondaryRate", new Integer(243));
        params.put("winterOnPeakPrimaryRate", new Integer(249));
        params.put("winterOnPeakSecondaryRate", new Integer(438));
        params.put("winterSemiPeakPrimaryRate", new Integer(176));
        params.put("winterSemiPeakSecondaryRate", new Integer(305));
        params.put("winterOffPeakPrimaryRate", new Integer(139));
        params.put("winterOffPeakSecondaryRate", new Integer(243));
        paramMaps.add(params);

        String drl = converter.compile(paramMaps, dis);
        Reader rdr = new StringReader( drl );
        kBuilder.add( ResourceFactory.newReaderResource(rdr), ResourceType.DRL);

The line in blue is throwing the exception. This code is very similar to the example code in Drools Expert guide.

Best,

Roger