Tag Archives: design

SOA – a quick view

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What is SOA?

SOA is standard based method of system development and integration

What are the benefits?

Reusability
Integration
Interoperability
Agile development
Scalability
Cost Efficient

What are all the ways to implement services?

Point to point approach
Vendor specific implementation
CORBA
Web services
SCA-style implementation

What are Services?

Building blocks of SOA
Interface and message structure definitions
Standard protocol for interoperability

What are SOA standards?

What is SCA [Service Component Architecture]?

SCA provides a programming model for building applications using SOA

What are the difference between SOA and SCA?

SOA is an approach or implementation style and SCA uses SOA to build a composite application
SOA is architectural style but SCA is assembly model and defines/design

What are the elements of SCA?

What is SDO [Service Data Object]?

Representation of data source in XML format and specifes methods to create, delete and modify data
Simplify and unify the way in which applications handles the data

What is EDN [Event Driven Network]?

To handle asynchronous messaging arising from a business event
Supports publish and subscribe model
Aligns with Event driven Architecture [EDA]

Database answers

OODesign concepts

Singleton pattern revisited

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Singleton pattern

Definition: At any point of time we ensure that there is only object created for the class

Example:
participant classes:

Singleton.java
SingletonClient.java(client)

Diagram:

Singleton.java

This class includes a static member variable singleton with private scope
the constructor is private so that no one can instantiate it
we have a getCurrentInstance() method to instantiate the class. If the instance is already available then the instance is returned to the caller otherwise it is newly created

public class Singleton {

 private static Singleton singleton = null;

 private Singleton(){

 }

 public static synchronized Singleton getCurrentInstance(){
 if(singleton == null){
 return new Singleton();
 }
 else{
 return singleton;
 }
 }

 public void sayHello(){
 System.out.println("Hello");
 }
}

SingletonClient.java

use getCurrentInstance() method to get the instance of Singleton class and use it.

 public class SingletonClient {

 public static void main(String[] args) {

 Singleton singleton =  Singleton.getCurrentInstance();
 singleton.sayHello();
 }
}

contract:

cannot instatiate more than once.
getCurrentInstance() return only one instance at any point of time

Implementing Prototype pattern

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Prototype pattern

Definition: the pattern is used to create a clone avoiding another creation. We clone the object if the cost of creating the object is expensive than cloning it.

Example:
participant classes:

Vinod.java
Rinku.java
Prototype.java
PrototpyeClient.java (client)

Diagram:

Prototype.java

This is an interface class defining signature for doClone() method. The return type is of Prototype type. This throws CloneNotSupportedException.

 public interface Prototype {
 public Prototype doClone() throws CloneNotSupportedException;
}

Vinod.java & Rinku.java

These are simple classes describing Vinod’s and Rinku’s characteristics. They have their attributes and their respective accessors defined in the class

These two classes implement the Prototype interface
doClone() method is implemented returning a new clone of the respective class

//Vinod.java
 public class Vinod implements Prototype,Cloneable{
 String name;
 String age;
 String sex;

 public String getName() {
 return "Vinod";
 }
 public String getAge() {
 return "25";
 }
 public String getSex() {
 return "Male";
 }
 @Override
 public Prototype doClone() throws CloneNotSupportedException {
 return (Prototype) this.clone();

 }

}

//Rinku.java

public class Rinku implements Prototype,Cloneable{
 String name;
 String age;
 String sex;

 public String getName() {
 return "Rinku";
 }
 public String getAge() {
 return "22";
 }
 public String getSex() {
 return "Female";
 }
 @Override
 public Prototype doClone() throws CloneNotSupportedException {
 return (Prototype) this.clone();

 }
}

PrototypeClient.java

Instantiating the objects and cloning the same

public class PrototypeClient {

 public static void main(String[] args) throws CloneNotSupportedException {

 Vinod vinod = new Vinod();
 Vinod vinod2 = (Vinod)vinod.doClone();

 System.out.println(vinod.hashCode() != vinod2.hashCode());
 System.out.println(vinod.getClass() == vinod2.getClass());

 }
}

contract:

x.clone() != x
x.clone().getClass() == x.getClass()