Design Patterns - Business Delegate


// Design Patterns - Structural - Business Delegate:

Business Delegate Pattern is used to decouple presentation tier and business 
tier. It is basically use to reduce communication or remote lookup functionality 
to business tier code in presentation tier code. In business tier we have 
following entities:

1. Client - Presentation tier code may be JSP, servlet or UI java code.
2. Business Delegate - A single entry point class for client entities to 
   provide access to Business Service methods.
3. LookUp Service - Lookup service object is responsible to get relative 
   business implementation and provide business object access to business 
   delegate object.
4. Business Service - Business Service interface. Concrete classes implement 
   this business service to provide actual business implementation logic.

We are going to create a Client, BusinessDelegate, BusinessService, 
LookUpService, JMSService and EJBService representing various entities of 
Business Delegate patterns.

// Step 1: Create BusinessService Interface.
public interface BusinessService {
   public void doProcessing();

// Step 2: Create concrete Service classes.
public class EJBService implements BusinessService {
   public void doProcessing() {
      System.out.println("Processing task by invoking EJB Service");

public class JMSService implements BusinessService {
   public void doProcessing() {
      System.out.println("Processing task by invoking JMS Service");

// Step 3: Create Business Lookup Service.
public class BusinessLookUp {
   public BusinessService getBusinessService(String serviceType){
         return new EJBService();
      } else {
         return new JMSService();

// Step 4: Create Business Delegate.
public class BusinessDelegate {
   private BusinessLookUp lookupService = new BusinessLookUp();
   private BusinessService businessService;
   private String serviceType;

   public void setServiceType(String serviceType){
      this.serviceType = serviceType;

   public void doTask(){
      businessService = lookupService.getBusinessService(serviceType);

// Step 5: Create Client.
public class Client {    
   BusinessDelegate businessService;

   public Client(BusinessDelegate businessService){
      this.businessService  = businessService;

   public void doTask(){        

// Step 6: Use BusinessDelegate and Client classes to demonstrate Business 
// Delegate pattern.

BusinessDelegate businessDelegate = new BusinessDelegate();

Client client = new Client(businessDelegate);

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