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## Chapter 15. Seam and JBoss Rules

Seam makes it easy to call JBoss Rules (Drools) rulebases from Seam components or jBPM process definitions.

## 15.1. Installing rules

The first step is to make an instance of `org.drools.RuleBase` available in a Seam context variable. For testing purposes, Seam provides a built-in component that compiles a static set of rules from the classpath. You can install this component via `components.xml`:

    <drools:rule-base name="policyPricingRules">

        <drools:rule-files>

            <value>policyPricingRules.drl</value>

        </drools:rule-files>

    </drools:rule-base>

This component compiles rules from a set of DRL (`.drl`) or decision table (`.xls`) files and caches an instance of `org.drools.RuleBase` in the Seam `APPLICATION` context. Note that it is quite likely that you will need to install multiple rule bases in a rule-driven application.

If you want to use a Drools DSL, you also need to specify the DSL definition:

    <drools:rule-base name="policyPricingRules" dsl-file="policyPricing.dsl">

        <drools:rule-files>

            <value>policyPricingRules.drl</value>

        </drools:rule-files>

    </drools:rule-base>

Support for Drools RuleFlow is also available and you can simply add a `.rf` or a `.rfm` as part of your rule files as:

            <drools:rule-base name="policyPricingRules" rule-files="policyPricingRules.drl, policyPricingRulesFlow.rf"/>

Note that when using the Drools 4.x RuleFlow (`.rfm`) format, you need to specify the -Ddrools.ruleflow.port=true system property on server startup. This is however still an experimental feature and we advise to use the Drools5 (`.rf`) format if possible.

If you want to register a custom consequence exception handler through the RuleBaseConfiguration, you need to write the handler, for example:

    @Scope(ScopeType.APPLICATION)

    @Startup

    @Name("myConsequenceExceptionHandler")

    public class MyConsequenceExceptionHandler implements ConsequenceExceptionHandler, Externalizable {

       public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {

       }

       public void writeExternal(ObjectOutput out) throws IOException {

       }

       public void handleException(Activation activation,

                                   WorkingMemory workingMemory,

                                   Exception exception) {

           throw new ConsequenceException( exception,

                                           activation.getRule() );

       }

    }

and register it:

    <drools:rule-base name="policyPricingRules" dsl-file="policyPricing.dsl" consequence-exception-handler="#{myConsequenceExceptionHandler}">

        <drools:rule-files>

            <value>policyPricingRules.drl</value>

        </drools:rule-files>

    </drools:rule-base>

In most rules-driven applications, rules need to be dynamically deployable, so a production application will want to use a Drools RuleAgent to manage the RuleBase. The RuleAgent can connect to a Drools rule server (BRMS) or hot deploy rules packages from a local file repository. The RulesAgent-managed RuleBase is also configurable in `components.xml`:

    <drools:rule-agent name="insuranceRules"

                        configurationFile="/WEB-INF/deployedrules.properties" />

The properties file contains properties specific to the RulesAgent. Here is an example configuration file from the Drools example distribution.

    newInstance=true
    url=http://localhost:8080/drools-jbrms/org.drools.brms.JBRMS/package/org.acme.insurance/fmeyer
    localCacheDir=/Users/fernandomeyer/projects/jbossrules/drools-examples/drools-examples-brms/cache
    poll=30
    name=insuranceconfig

It is also possible to configure the options on the component directly, bypassing the configuration file.

    <drools:rule-agent name="insuranceRules"

       url="http://localhost:8080/drools-jbrms/org.drools.brms.JBRMS/package/org.acme.insurance/fmeyer"

       local-cache-dir="/Users/fernandomeyer/projects/jbossrules/drools-examples/drools-examples-brms/cache"

       poll="30"

       configuration-name="insuranceconfig" />

Next, we need to make an instance of `org.drools.WorkingMemory` available to each conversation. (Each `WorkingMemory` accumulates facts relating to the current conversation.)

    <drools:managed-working-memory name="policyPricingWorkingMemory" auto-create="true" rule-base="#{policyPricingRules}"/>

Notice that we gave the `policyPricingWorkingMemory` a reference back to our rule base via the `ruleBase` configuration property.

We can also add means to be notified of rule engine events, including rules firing, objects being asserted, etc. by adding event listeners to WorkingMemory.

    <drools:managed-working-memory name="policyPricingWorkingMemory" auto-create="true" rule-base="#{policyPricingRules}">

        <drools:event-listeners>

            <value>org.drools.event.DebugWorkingMemoryEventListener</value>

            <value>org.drools.event.DebugAgendaEventListener</value>

        </drools:event-listeners>

    </drools:managed-working-memory>

## 15.2. Using rules from a Seam component

We can now inject our `WorkingMemory` into any Seam component, assert facts, and fire rules:

    @In WorkingMemory policyPricingWorkingMemory;

    @In Policy policy;

    @In Customer customer;

    public void pricePolicy() throws FactException

    {

        policyPricingWorkingMemory.insert(policy);

        policyPricingWorkingMemory.insert(customer);

        // if we have a ruleflow, start the process

        policyPricingWorkingMemory.startProcess(startProcessId)

        policyPricingWorkingMemory.fireAllRules();

    }

## 15.3. Using rules from a jBPM process definition

You can even allow a rule base to act as a jBPM action handler, decision handler, or assignment handler — in either a pageflow or business process definition.

    <decision name="approval">

        <handler class="org.jboss.seam.drools.DroolsDecisionHandler">

            <workingMemoryName>orderApprovalRulesWorkingMemory</workingMemoryName>

            <!-- if a ruleflow was added -->

            <startProcessId>approvalruleflowid</startProcessId>

            <assertObjects>

                <element>#{customer}</element>

                <element>#{order}</element>

                <element>#{order.lineItems}</element>

            </assertObjects>

        </handler>

        <transition name="approved" to="ship">

            <action class="org.jboss.seam.drools.DroolsActionHandler">

                <workingMemoryName>shippingRulesWorkingMemory</workingMemoryName>

                <assertObjects>

                    <element>#{customer}</element>

                    <element>#{order}</element>

                    <element>#{order.lineItems}</element>

                </assertObjects>

            </action>

        </transition>

        <transition name="rejected" to="cancelled"/>

    </decision>

The `<assertObjects>` element specifies EL expressions that return an object or collection of objects to be asserted as facts into the `WorkingMemory`.

The `<retractObjects>` element on the other hand specifies EL expressions that return an object or collection of objects to be retracted from the `WorkingMemory`.

There is also support for using Drools for jBPM task assignments:

    <task-node name="review">

        <task name="review" description="Review Order">

            <assignment handler="org.jboss.seam.drools.DroolsAssignmentHandler">

                <workingMemoryName>orderApprovalRulesWorkingMemory</workingMemoryName>

                <assertObjects>

                    <element>#{actor}</element>

                    <element>#{customer}</element>

                    <element>#{order}</element>

                    <element>#{order.lineItems}</element>

                </assertObjects>

            </assignment>

        </task>

        <transition name="rejected" to="cancelled"/>

        <transition name="approved" to="approved"/>

    </task-node>

Certain objects are available to the rules as Drools globals, namely the jBPM `Assignable`, as `assignable` and a Seam `Decision` object, as `decision`. Rules which handle decisions should call `decision.setOutcome("result")` to determine the result of the decision. Rules which perform assignments should set the actor id using the `Assignable`.

    package org.jboss.seam.examples.shop

    import org.jboss.seam.drools.Decision

    global Decision decision

    rule "Approve Order For Loyal Customer"
      when
        Customer( loyaltyStatus == "GOLD" )
        Order( totalAmount <= 10000 )
      then
        decision.setOutcome("approved");
    end

    package org.jboss.seam.examples.shop

    import org.jbpm.taskmgmt.exe.Assignable

    global Assignable assignable

    rule "Assign Review For Small Order"
      when
        Order( totalAmount <= 100 )
      then
        assignable.setPooledActors( new String[] {"reviewers"} );
    end

## Note

You can find out more about Drools at http://www.drools.org

## Caution

Seam comes with enough of Drools' dependencies to implement some simple rules. If you want to add extra capabilities to Drools you should download the full distribution and add in extra dependencies as needed.

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