Integration of Drools and spring to perform business logic validation in JSF

In a previous post I explained how to use AOP to perform custom validation in JSF. Here I will show how you can use the business logic framework Drools to perform validation based upon external (business) rules in conjunction with springframework.

In this example I will perform the bussiness rules validation inside an advice class, but you can implement the same mechanism to perform that validation inside a JSF backing bean or in a spring bean.

Inside your application-context.xml file add your advice in the following way:

<bean id="validatorAspect" 
   class="com.foo.aspects.BackingBeanValidatorAdvice" 
   factory-method="aspectOf">
<property name="resources">
<list>
<value>/com/foo/business/rules.drl</value>
</list>
</property>
</bean>

I'm assuming you have basic knowledge of Drool, I will not get into syntax details here, there is a lot of documentation in Drool's site; instead I will just present a simple validation rule file rules.drl:


package com.foo.business

import com.foo.model.ModelBean;
import com.foo.aspects.Error;

query "Error" ()
    error : Error()
end


rule "Rule 1"
when
   ModelBean( id == 32 && internalId not matches "(J|P|R) ([0-9]){6}")
then
   Error err = new Error();
   err.setSummary("Error in Model Bean. ");
   err.setDetail("Internal Id not matches format: (J, P o R) followed by whitespace and 6 digits");
   insert(err);
end

Error is just a simple Pojo containing two properties (summary and detail).

Then, you must fire the validation inside the advice class:

public aspect BackingBeanValidatorAdvice {

    private KnowledgeBase kbase;

    private StatefulKnowledgeSession ksession;
    
    private String[] resources;

    pointcut doSaveChanges() : execution(* com.foo.beans.BackingBean.saveChanges(..));

    void around() : doSaveChanges() {
        FacesContext context = FacesContext.getCurrentInstance();
        ModelBean mbean = context.getApplication().evaluateExpressionGet(context, "#{bBean.selected}", ModelBean.class); 

        this.init();
        this.getKsession().insert(mbean);
        this.getKsession().fireAllRules();

        QueryResults results = this.getKsession().getQueryResults("Error");
        if (results.size() > 0) {
            for (QueryResultsRow row : results) {
                Error err = (Error) row.get("error");
                context.addMessage("error", new FacesMessage(FacesMessage.SEVERITY_ERROR, err
                        .getSummary(), err.getDetail()));
            }
        }
        proceed();
    }

    public void init() {
        if (this.getKbase() == null) {
            KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
            for (int i = 0; i < this.getResources().length; i++) {
                String rule = this.getResources()[i];
                kbuilder.add(ResourceFactory.newInputStreamResource(this.getClass().getResourceAsStream(rule)),
                    ResourceType.DRL);
            }
    
            if (kbuilder.hasErrors()) {
                System.out.println(kbuilder.getErrors());
                return;
            }
            Collection < KnowledgePackage > kpkgs = kbuilder.getKnowledgePackages();
            KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
            kbase.addKnowledgePackages(kpkgs);
            this.setKbase(kbase);
        }
        this.setKsession(this.getKbase().newStatefulKnowledgeSession());       
    }
    
    public StatefulKnowledgeSession getKsession() {
        return ksession;
    }

    public void setKsession(StatefulKnowledgeSession ksessionToSet) {
        this.ksession = ksessionToSet;
    }

    public String[] getResources() {
        return resources;
    }

    public void setResources(String[] resourcesToSet) {
        this.resources = resourcesToSet;
    }

    public KnowledgeBase getKbase() {
        return kbase;
    }

    public void setKbase(KnowledgeBase kbase) {
        this.kbase = kbase;
    }    
}

That's it. In case the validation fails, a FacesMessage is added to the FacesContext and JSF is responsible for handling and showing the error in a jsf page, eg: <h:messages .../>