Composite Entity Pattern

The Composite Entity Pattern is used in EJB persistence mechanisms. A composite entity is an EJB entity bean which represents a graph of objects. When a composite entity is updated, the internal dependent object beans are automatically updated due to the management by the EJB entity bean. The following are the participants of the composite entity bean.

• Composite Entity - It is the primary entity bean. It can be coarse-grained, or it can contain a coarse-grained object to be used for the purpose of long term persistence.

• Coarse-Grained Object - This object contains dependent objects. It has its own life cycle and also manages the life cycle of dependent objects.

• Dependent Object - A dependent object is an object that has its life cycle managed by the coarse-grained object.

• Strategies - Strategies represent how to implement a composite entity.

Implementation

We will create a CompositeEntity object acting as a composite entity. CoarseGrainedObject is a class that contains dependent objects.

CompositeEntityPatternDemo, our demo class, will use Client class to demonstrate the use of the composite entity pattern.

Step 1

Create dependent objects.

DependentObject1.java

public class DependentObject1 {

   private String data;

   public void setData(String data){
      this.data = data; 
   } 

   public String getData(){
      return data;
   }
}

DependentObject2.java

public class DependentObject2 {

   private String data;

   public void setData(String data){
      this.data = data; 
   } 

   public String getData(){
      return data;
   }
}

Step 2

Create a coarse-grained object.

CoarseGrainedObject.java

public class CoarseGrainedObject {
   DependentObject1 do1 = new DependentObject1();
   DependentObject2 do2 = new DependentObject2();

   public void setData(String data1, String data2){
      do1.setData(data1);
      do2.setData(data2);
   }

   public String[] getData(){
      return new String[] {do1.getData(),do2.getData()};
   }
}

Step 3

Create a composite entity.

CompositeEntity.java

public class CompositeEntity {
   private CoarseGrainedObject cgo = new CoarseGrainedObject();

   public void setData(String data1, String data2){
      cgo.setData(data1, data2);
   }

   public String[] getData(){
      return cgo.getData();
   }
}

Step 4

Create a client class that uses the composite entity.

Client.java

public class Client {
   private CompositeEntity compositeEntity = new CompositeEntity();

   public void printData(){
      for (int i = 0; i < compositeEntity.getData().length; i++) {
         System.out.println("Data: " + compositeEntity.getData()[i]);
      }
   }

   public void setData(String data1, String data2){
      compositeEntity.setData(data1, data2);
   }
}

Step 5

Use Client to demonstrate the use of the composite entity design pattern.

CompositeEntityPatternDemo.java

public class CompositeEntityPatternDemo {
   public static void main(String[] args) {
       Client client = new Client();
       client.setData("Test", "Data");
       client.printData();
       client.setData("Second Test", "Data1");
       client.printData();
   }
}

Step 6

Execute the program, output result:

Data: Test
Data: Data
Data: Second Test
Data: Data1