GenericRulesEngine: an Abstract Class
Originally published .
This is my take on how to implement rules engines in a project. I’m still working a few things out but you get the idea.
package com.vifprogram.tie;
import java.io.InputStream;
import java.rmi.RemoteException;
import javax.rules.InvalidRuleSessionException;
import javax.rules.RuleRuntime;
import javax.rules.RuleServiceProvider;
import javax.rules.RuleServiceProviderManager;
import javax.rules.StatelessRuleSession;
import javax.rules.admin.LocalRuleExecutionSetProvider;
import javax.rules.admin.RuleAdministrator;
import javax.rules.admin.RuleExecutionSet;
import javax.rules.admin.RuleExecutionSetDeregistrationException;
import org.drools.jsr94.rules.RuleServiceProviderImpl;
/**
* This is the base class for you to write your own rules driven things.
* @author shawn
*
*/
public abstract class GenericRulesEngine {
private final String RULE_SERVICE_PROVIDER = "http://drools.org/";
protected String RULE_URI = null;
protected StatelessRuleSession _statelessRuleSession;
protected RuleAdministrator _ruleAdministrator;
private boolean _clean = false;
public GenericRulesEngine() {
super();
RULE_URI = getRuleURI();
}
/**
* Returns the string such as MyClassName.drl
* @return
*/
protected abstract String getRuleURI();
/**
* you could implement just this...
* return AssignmentManager.class.getResourceAsStream(RULE_URI);
* or invent some fancier method of loading the resources...
* @return
*/
protected abstract InputStream getRules();
/**
* runs the cleanup
*/
protected void finalize() throws Throwable {
if(!_clean) {
cleanUp();
}
}
/**
* set up the rules engine
*
*/
protected void prepare() throws Exception {
RuleServiceProviderManager.registerRuleServiceProvider(
RULE_SERVICE_PROVIDER, RuleServiceProviderImpl.class );
RuleServiceProvider ruleServiceProvider =
RuleServiceProviderManager.getRuleServiceProvider(RULE_SERVICE_PROVIDER);
_ruleAdministrator = ruleServiceProvider.getRuleAdministrator( );
LocalRuleExecutionSetProvider ruleSetProvider =
_ruleAdministrator.getLocalRuleExecutionSetProvider(null);
/*
* This is the point at which the rules file is loaded. If you wanted
* the rules file to load from a different location you would change
* this here:
*/
InputStream rules = getRules();
RuleExecutionSet ruleExecutionSet =
ruleSetProvider.createRuleExecutionSet(rules, null);
_ruleAdministrator.registerRuleExecutionSet(RULE_URI, ruleExecutionSet, null);
RuleRuntime ruleRuntime = ruleServiceProvider.getRuleRuntime();
_statelessRuleSession =
(StatelessRuleSession) ruleRuntime.createRuleSession(
RULE_URI, null, RuleRuntime.STATELESS_SESSION_TYPE );
}
/**
* @throws RemoteException
* @throws InvalidRuleSessionException
* @throws RuleExecutionSetDeregistrationException
*/
private void cleanUp() throws InvalidRuleSessionException, RemoteException, RuleExecutionSetDeregistrationException {
_clean = true;
_statelessRuleSession.release();
_ruleAdministrator.deregisterRuleExecutionSet(RULE_URI, null);
}
BTW: I ripped off most of this I’m sure. I just can’t remember who from.