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Design_Pattern - Composite Entity Pattern


Composite Entity pattern is used in EJB persistence mechanism. A Composite entity is an EJB entity bean which represents a graph of objects. When a composite entity is updated, internally dependent objects beans get updated automatically as being managed by EJB entity bean. Following are the participants in Composite Entity Bean.
  • Composite Entity - It is primary entity bean. It can be coarse grained or can contain a coarse grained object to be used for persistence purpose.
  • Coarse-Grained Object - This object contains dependent objects. It has its own life cycle and also manages life cycle of dependent objects.
  • Dependent Object - Dependent object is an object which depends on coarse grained object for its persistence lifecycle.
  • Strategies - Strategies represent how to implement a Composite Entity.
Implementation

We are going to create CompositeEntity object acting as CompositeEntity. CoarseGrainedObject will be a class which contains dependent objects. CompositeEntityPatternDemo, our demo class, will use Client class to demonstrate use of 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 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 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 Client class to use 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 the Client to demonstrate Composite Entity design pattern usage.

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

Verify the output.
Data: Test
Data: Data
Data: Second Test
Data: Data1
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