Business delegate pattern

<h2 id="structure">Structure</h2>
<p>Requests to access underlying business services are sent from clients, and lookup services are used by business delegates to locate the business service components.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<h3>Components</h3>
<p>Basic components are Business delegate, Lookup service and business service.
</p>
<h4>Business delegate</h4>
<p>Control and protection are provided through business delegate which can have two types of structures, without ID and with ID, where ID is a string version of the reference to a remote object such as EJBHome or EJBObject.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p>
<h4>Lookup service</h4>
<p>Business service is located by lookup service which is used by the business delegate. The implementation details of business service lookup is encapsulated by lookup service.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a>
</p>
<h4>Business service</h4>
<p>This a business-tier component, such as an enterprise bean or a JMS component, which provides the required service to the client.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p>
<h2 id="consequences">Consequences</h2>
<p>Some consequences are as follows:
</p>
<ul><li>More flexibility and maintainability as intermediate business delegate layer decouples the business layer from the presentation layer.</li>
<li>Business delegate exposes a uniform API to the presentation tier to access business logic.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></li></ul>
<h2 id="concerns">Concerns</h2>
<p>Following concerns can be considered:
</p>
<ul><li>Maintenance due to the extra layer that increases the number of classes in the application.</li>
<li>Business delegate should take care of the changes of the remote business object interfaces, and these types of changes are rare.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></li></ul>
<h2 id="sample-code">Sample code</h2>
<p>A sample code for a Professional Services Application (PSA), where a Web-tier client needs to access a session bean that implements the session facade pattern, is provided below.
</p><p>Resource Delegate:
</p>
public class ResourceDelegate {

// Remote reference for Session Facade
    private ResourceSession session;

// Class for Session Facade's Home object
    private static final Class homeClazz =
    corepatterns.apps.psa.ejb.ResourceSessionHome.class;

// Default Constructor. Looks up home and connects
    // to session by creating a new one
    public ResourceDelegate() throws ResourceException {
        try {
            ResourceSessionHome home = (ResourceSessionHome)
                ServiceLocator.getInstance().getHome(
                    "Resource", homeClazz);
            session = home.create();
        } catch(ServiceLocatorException ex) {
            // Translate Service Locator exception into
            // application exception
            throw new ResourceException(...);
        } catch(CreateException ex) {
            // Translate the Session create exception into
            // application exception
            throw new ResourceException(...);
        } catch(RemoteException ex) {
            // Translate the Remote exception into
            // application exception
            throw new ResourceException(...);
        }
    }

public BusinessDelegate(String id)
        throws ResourceException {
        super();
        reconnect(id);
    }

public String getID() {
        try {
            return ServiceLocator.getId(session);
        } catch (Exception e) {
            // Throw an application exception
        }
    }

public void reconnect(String id) 
        throws ResourceException {
        try {
            session = (ResourceSession)ServiceLocator.getService(id);
        } catch (RemoteException ex) {
            // Translate the Remote exception into
            // application exception
            throw new ResourceException(...);
        }
    }

public ResourceTO setCurrentResource(
        String resourceId)
        throws ResourceException {
        try {
            return session.setCurrentResource(resourceId);
        } catch (RemoteException ex) {
            // Translate the service exception into
            // application exception
            throw new ResourceException(...);
        }
    }

public ResourceTO getResourceDetails()
        throws ResourceException {

try {
            return session.getResourceDetails();
        } catch(RemoteException ex) {
            // Translate the service exception into
            // application exception
            throw new ResourceException(...);
        }
    }

public void setResourceDetails(ResourceTO vo)
        throws ResourceException {
        try {
            session.setResourceDetails(vo);
        } catch(RemoteException ex) {
            throw new ResourceException(...);
        }
    }

public void addNewResource(ResourceTO vo)
        throws ResourceException {
        try {
            session.addResource(vo);
        } catch(RemoteException ex) {
            throw new ResourceException(...);
        }
    }

// all other proxy method to session bean
    ...
}
<p><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a>
</p><h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Service_locator_pattern/gjkmaDFg">service locator pattern</a></li>
<li><a href="/facts/Proxy_pattern/CHHyzXbd">Proxy pattern</a></li>
<li><a href="/facts/Adapter_pattern/jbLgy7ct">Adapter pattern</a></li>
<li><a href="/facts/Broker_Pattern/kCJwJ1XW">Broker Pattern</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Screening Technical Design Document – Version 2.0. Indiana, USA: Indiana state. p. 7. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Kayal, D. (2008). Pro Java EE Spring Patterns. New York: Apress. pp. 161–166. <a href="https://archive.org/details/projavaeespringp00kaya" target="_blank">https://archive.org/details/projavaeespringp00kaya</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
<li id="fn:10"><p>Kayal, D. (2008). Pro Java EE Spring Patterns. New York: Apress. pp. 161–166. <a href="https://archive.org/details/projavaeespringp00kaya" target="_blank">https://archive.org/details/projavaeespringp00kaya</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li>
<li id="fn:11"><p>Kayal, D. (2008). Pro Java EE Spring Patterns. New York: Apress. pp. 161–166. <a href="https://archive.org/details/projavaeespringp00kaya" target="_blank">https://archive.org/details/projavaeespringp00kaya</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li>
<li id="fn:12"><p>"Core J2EE Patterns – Business Delegate". Oracle. Oracle. Retrieved 22 June 2016. <a href="http://www.oracle.com/technetwork/java/businessdelegate-137562.html" target="_blank">http://www.oracle.com/technetwork/java/businessdelegate-137562.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li>
</ol>

Business delegate pattern open-in-new

Business delegate pattern