Re: [rules-users] Integration of Drools with Hadoop
On 31/10/2010 05:35, Roger Smith wrote:
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:///%5C%5Chome%5Cpranab%5CProjects%5Cgridx%5C>";
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);
ResourceFactory.newFileResource just creates a file object but cleaning
up the paths.
public FileSystemResource(File file) {
if ( file == null ) {
throw new IllegalArgumentException( "File must not be null" );
}
this.file = new File( StringUtils.cleanPath(file.getPath()) );
}
The code is borrowed from Spring and uses the sme cleanPath logic. Once
the file is created it just creates the stream as so:
public InputStream getInputStream() throws IOException {
this.lastRead = getLastModified();
return new FileInputStream(this.file);
}
So it's pretty basic, the stack trace with line numbers may help. But I
suspect you'll need to do a debug and step into the drools code at the
point where you get the nullpointer and see what's going on.
Mark
It works fine as a stand alone app, outside hadoop
Roger Smith
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