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'''Business delegate''' is a [[Java Platform, Enterprise Edition|Java EE]] design pattern.
<ref name=":o_cjp">{{Cite web|url = http://www.oracle.com/technetwork/java/businessdelegate-137562.html|title = Core J2EE Patterns -– Business Delegate|access-date = |accessdate = 22 June 2016|website = Oracle|publisher = Oracle|last = |first = }}</ref> This pattern is directingdirected totowards reducereducing the [[Coupling (computer programming)|coupling]] in between business serivesservices and the connected presentation- tier, and to hide the implementation details of services (including lookup and accessabilityaccessibility of [[Enterprise JavaBeans|EJB]] architecture).<ref name=":o_cjp"/><ref name=":stdd">{{Cite book|title = Screening Technical Design Document -– Version 2.0|last = |first = |publisher = Indiana state|year = |___location = Indiana, USA|volume = |pages = 7}}</ref> Business delegates acts as an adaptor to invoke business objects from the presentation tier.<ref name=":pjeesp">{{Cite book|title = Pro Java EE Spring Patterns|url = https://archive.org/details/projavaeespringp00kaya|url-access = limited|last = Kayal|first = D.|publisher = Apress|year = 2008|___location = New York|volume = |pages = [https://archive.org/details/projavaeespringp00kaya/page/n182 161-166]–166}}</ref>
 
==Structure==
Requests to access underlying business services are sent from clients, and lookup services are used by business delegates to locate the business service components.<ref name=":o_cjp"/>
 
===Components===
Basic components are Business delegate, Lookup service and business service.
 
====Business delegate====
Control and protection are provided through business delegate which can have two types of constructuresstructures, without ID and with ID, where ID is a string version of the reference to a remote object such as EJBHome or EJBObject.<ref name=":o_cjp"/>
 
ID is a string version of the reference to a remote object such as EJBHome or EJBObject.<ref name=":o_cjp"/>
====Lookup Serviceservice====
Business service is located by lookup service which is used by the business delegate. theThe implementation details of business service lookup is encapsulated by lookup service.<ref name=":o_cjp"/>
 
====Business Service====
====Business service====
This a business-tier component, such as an enterprise bean or a JMS component, which provides the required service to the client. <ref name=":o_cjp"/>
This a business-tier component, such as an enterprise bean or a JMS component, which provides the required service to the client.<ref name=":o_cjp"/>
 
==Consequences==
Some consequences are as follows:
 
* More flexibility and maintanabilitymaintainability as intermediate business delegate layer decouples the business layer from the presentation layer.
* Business delegate exposes a uniform API to the presentatoinpresentation tier to access business logic.<ref name=":pjeespo_cjp"/><ref name=":o_cjppjeesp"/>
 
==Concerns==
FollwingFollowing concersconcerns can be considered:
* Maintenance due to the extra layer that incresesincreases the number of classes in the application.
* Business delegate should take care of the changes of the remote business object interfaces, and these types of changes are rare.<ref name=":pjeesp"/>
 
==Sample code==
A sample code for a Professional Services Application (PSA), where a Web-tier cleintclient needs to access a session bean that implements the session façadefacade pattern, is provided below.
 
Resource Delegate:
<Sourcesyntaxhighlight lang="java">
 
 
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 {
public BusinessDelegate(String id)
super();
throws ResourceException {
super reconnect(id);
reconnect(id);
}
 
public String getID() {
try {
return ServiceLocator.getId(session);
} catch (Exception e) {
// Throw an application exception
}
}
 
public void reconnect(public String idgetID() {
throws ResourceException try {
return ServiceLocator.getId(session);
try {
session = } catch (ResourceSessionException e) {
// Throw an application ServiceLocator.getService(id);exception
} catch (RemoteException ex) {}
// Translate the Remote exception into
// application exception
throw new ResourceException(...);
}
}
 
public void reconnect(String id)
throws ResourceException {
public ResourceTO setCurrentResource(
String resourceId) try {
session = (ResourceSession)ServiceLocator.getService(id);
throws ResourceException {
} catch (RemoteException ex) {
try {
// Translate the Remote exception into
return session.setCurrentResource(resourceId);
// application exception
} catch (RemoteException ex) {
throw new ResourceException(...);
// Translate the service exception into
// application exception}
throw new ResourceException(...);
}
}
 
public ResourceTO getResourceDetailssetCurrentResource()
String resourceId)
throws ResourceException {
throws ResourceException {
 
try {
return session.getResourceDetailssetCurrentResource(resourceId);
} catch (RemoteException ex) {
// Translate the service exception into
// application exception
throw new ResourceException(...);
}
}
}
 
public void setResourceDetails(public ResourceTO vogetResourceDetails()
throws ResourceException {
try {
session.setResourceDetails(vo);
} catch(RemoteException ex) {
throw new ResourceException(...);
}
}
 
try {
public void addNewResource(ResourceTO vo)
return session.getResourceDetails();
throws ResourceException {
} catch (RemoteException ex) {
try {
// Translate the service exception into
session.addResource(vo);
// application exception
} catch(RemoteException ex) {
throw new ResourceException(...);
}
}
}
 
public void setResourceDetails(ResourceTO vo)
// all other proxy method to session bean
throws ResourceException {
...
try {
}
session.setResourceDetails(vo);
</source><ref name=":o_cjp"/>
} catch (RemoteException ex) {
Remote interface for ResouceSession:
throw new ResourceException(...);
<source lang="java">
}
 
 
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 Stringvoid getIDaddNewResource()ResourceTO {vo)
throws ResourceException {
try {
try {
return ServiceLocator.getId(session);
session.addResource(vo);
} catch (Exception e) {
} catch (RemoteException ex) {
// Throw an application exception
throw new ResourceException(...);
}
}
}
 
// all other proxy method to session bean
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
...
}
</sourcesyntaxhighlight><ref name=":o_cjp"/>
 
==See also==
Line 259 ⟶ 147:
 
{{Design Patterns Patterns}}
 
[[Category:Software design patterns]]
[[Category:Articles with example Java code]]
Retrieved from "https://en.wikipedia.org/wiki/Business_delegate_pattern"