Composite Entity Pattern in Java: Streamlining Persistent Object Management

About 3 min

Also known as

Coarse-Grained Entity

Intent of Composite Entity Design Pattern

The Composite Entity design pattern in Java is aimed at managing a set of interrelated persistent objects as if they were a single entity. It is commonly used in enterprise applications, particularly within the context of Enterprise JavaBeans (EJB) and similar enterprise frameworks, to represent graph-based data structures within business models. This pattern enables clients to treat these complex structures as a single unit, simplifying operations and interactions.

Detailed Explanation of Composite Entity Pattern with Real-World Examples

Real-world example

Consider a university registration system where a "Student" entity is a composite entity. Each "Student" object includes several dependent objects: personal details, course enrollments, grades, and payment information. Instead of managing each of these aspects separately, the Composite Entity design pattern allows the university system to treat the "Student" as a single entity. This simplifies operations such as enrolling a student in a new course, updating grades, and processing payments, since all related actions can be managed through the composite "Student" object.

In plain words

The Composite Entity pattern in Java allows a set of related persistent objects to be represented and managed by a unified object, simplifying enterprise application design.

Wikipedia says

Composite entity is a Java EE Software design pattern and it is used to model, represent, and manage a set of interrelated persistent objects rather than representing them as individual fine-grained entity beans, and also a composite entity bean represents a graph of objects.

Programmatic Example of Composite Entity in Java

For a console, there may be many interfaces that need to be managed and controlled. Using the composite entity pattern, dependent objects such as messages and signals can be combined and controlled using a single object.

We need a generic solution for the problem. To achieve this, let's introduce a generic Composite Entity Pattern.

public abstract class DependentObject<T> {

    T data;

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

    public T getData() {
        return data;
    }
}

public abstract class CoarseGrainedObject<T> {

    DependentObject<T>[] dependentObjects;

    public void setData(T... data) {
        IntStream.range(0, data.length).forEach(i -> dependentObjects[i].setData(data[i]));
    }

    public T[] getData() {
        return (T[]) Arrays.stream(dependentObjects).map(DependentObject::getData).toArray();
    }
}

The specialized composite entity console inherit from this base class as follows.

public class MessageDependentObject extends DependentObject<String> {

}

public class SignalDependentObject extends DependentObject<String> {

}

public class ConsoleCoarseGrainedObject extends CoarseGrainedObject<String> {

    @Override
    public String[] getData() {
        super.getData();
        return new String[] {
                dependentObjects[0].getData(), dependentObjects[1].getData()
        };
    }

    public void init() {
        dependentObjects = new DependentObject[] {
                new MessageDependentObject(), new SignalDependentObject()};
    }
}

public class CompositeEntity {

    private final ConsoleCoarseGrainedObject console = new ConsoleCoarseGrainedObject();

    public void setData(String message, String signal) {
        console.setData(message, signal);
    }

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

Now managing the assignment of message and signal objects with the composite entity console.

public App(String message, String signal) {
    var console = new CompositeEntity();
    console.init();
    console.setData(message, signal);
    Arrays.stream(console.getData()).forEach(LOGGER::info);
    console.setData("Danger", "Red Light");
    Arrays.stream(console.getData()).forEach(LOGGER::info);
}

When to Use the Composite Entity Pattern in Java

Useful in Java enterprise applications where business objects are complex and involve various interdependent persistent objects.
Ideal for scenarios where clients need to work with a unified interface to a set of objects rather than individual entities.
Applicable in systems that require a simplified view of a complex data model for external clients or services.

Real-World Applications of Composite Entity Pattern in Java

Enterprise applications with complex business models, particularly those using EJB or similar enterprise frameworks.
Systems requiring abstraction over complex database schemas to simplify client interactions.
Applications that need to enforce consistency or transactions across multiple persistent objects in a business entity.

Benefits and Trade-offs of Composite Entity Pattern

Benefits:

Simplifies client interactions with complex entity models by providing a unified interface.
Enhances reusability and maintainability of the business layer by decoupling client code from the complex internals of business entities.
Facilitates easier transaction management and consistency enforcement across a set of related persistent objects.

Trade-offs:

May introduce a level of indirection that could impact performance.
Can lead to overly coarse-grained interfaces that might not be as flexible for all client needs.
Requires careful design to avoid bloated composite entities that are difficult to manage.

Decorator: For dynamically adding behavior to individual objects within the composite entity without affecting the structure.
Facade: Provides a simplified interface to a complex subsystem, similar to how a composite entity simplifies access to a set of objects.
Flyweight: Useful for managing shared objects within a composite entity to reduce memory footprint.