JBoss DSL

From Kb

Expanders and DSL allow you to write your rules in a natural language, then translate to JBoss rules language (think find and replace).

Samples below are from JBoss Rules Trouble Ticket Sample

Contents 1 Related Links 2 Rules 3 Domain Specific Language (DSL) 4 Java Code to run this 5 Java Code to load rules from classpath

Related Links

Blog Entry on Rules Course

Rules

To be able to use the following natural language rules

package org.drools.examples
expander ticketing.dsl


rule "New Ticket"
	salience 10
	when		
		There is a customer ticket with status of "New"
	then
		Log "New"		
end
 
rule "Silver Priorty"
	#if after a certain time, we still have an issue, then escalate
	duration 3000
	when			
    	There is a "Silver" customer with a ticket status of "New"						
	then
		Escalate the ticket
end

rule "Gold Priority"
	duration 1000
	when
		There is a "Gold" customer with a ticket status of "New"
	then
		Escalate the ticket
end

rule "Platinum Priority"
	#we don't want to make the high rollers wait !
	when		
		There is a "Platinum" customer with a ticket status of "New"
	then
		Escalate the ticket
end


 
rule "Escalate"
	when
		There is a customer ticket with status of "Escalate" 
	then 
		Send escalation email
end

rule "Done"
	when
		There is a customer ticket with status of "Done" 
	then 
		Log "Done"
end

# This is the same as the non DSL version. This could be kept in another file of course.
function void sendEscalationEmail( Customer customer, Ticket ticket ) {
	System.out.println( "Email : " + ticket );
}

#hey, the imports can appear anywhere !
import org.drools.examples.TroubleTicketExampleWithDSL.Customer;
import org.drools.examples.TroubleTicketExampleWithDSL.Ticket;

Domain Specific Language (DSL)

You need a DSL to map this to more technical language.

#place your comments here - this is just a description for your own purposes.
[when]There is a customer ticket with status of "{status}"=customer : Customer( )   ticket : Ticket( customer == customer, status == "{status}" )
[when]There is a "{subscription}" customer with a ticket status of "{status}"=customer : Customer(subscription == "{subscription}") ticket : Ticket( customer == customer, status == "{status}")
[then]Log "{message}"=System.out.println("{message} " + ticket);
[then]Escalate the ticket=ticket.setStatus("Escalate"); modify(ticket);
[then]Send escalation email=sendEscalationEmail( customer, ticket );

Java Code to run this

The addPackageFromDrl( getSource(), getDSL()) loads not only our rules , but the mapping to carry out the translation.

        final PackageBuilder builder = new PackageBuilder();
        builder.addPackageFromDrl( getSource(),
                                   getDSL() );

        final RuleBase ruleBase = RuleBaseFactory.newRuleBase();
        ruleBase.addPackage( builder.getPackage() );

        final WorkingMemory workingMemory = ruleBase.newWorkingMemory();

        final WorkingMemoryFileLogger logger = new WorkingMemoryFileLogger( workingMemory );
        logger.setFileName( "log/state" );

... assert objects into working memory ...       

        workingMemory.fireAllRules();

      

Java Code to load rules from classpath

Allows our rules to be deployed to a Tomcat instance

    /**
     * Searches for a file via the local filesystem , then via the Classpath
     *
     * @param fileName to search for
     * @return InputStream containing the opened file
     */
    private InputStream getFileIfExists(String fileName) throws SearchException {

        // Local Variables
        InputStream rIStream = null;

        log.debug("Searching for File name:" + fileName);

        // The next line creates one execution of the process definition.
        // After construction the process execution has one main path
        // of execution (the root token) that is positioned in the
        // startstate.
        try {
            rIStream = new FileInputStream(fileName);

        } catch (FileNotFoundException fnfe1) {
            log
                    .debug("Could not find resource as file - attempting the classpath");

            try {
                ClassPathResource myClassPathReader = new ClassPathResource(
                        fileName);
                rIStream = myClassPathReader.getInputStream();
                log.debug("Found File via Classpath at path:" + myClassPathReader.getPath() + " file:" + myClassPathReader.getFile());

            } catch (Exception fnfe2) {
                log.debug("Returning Null as could not find file" + fileName + "locally or on classpath");
                //log.info("Could not find resource as file", fnfe1);
                //log.info("Could not find resource on classpath", fnfe2);

                // we will return null
            }
        }

        return rIStream;

    }