Seam FrameworkCommunity Documentation
Seam makes it easy to call JBoss Rules (Drools) rulebases from Seam components or jBPM process definitions.
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>
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();
}
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");
endpackage 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"} );
endYou can find out more about Drools at http://www.drools.org
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.