Session Facade Pattern

Problem: Multiple Network Round Trips

Here BusinessDelegate comp of Client App is having multiple round trips with multiple external comps which leads to performance issues (problem).

Solution: Session Facade Aggregates Calls

Implementation

// Session Facade interface
public interface IStockFacade {
    StockDetailsDTO getCompleteStockInfo(String stockName);
}

// Session Facade implementation: aggregates 3 services
public class StockFacadeImpl implements IStockFacade {
    private final IGetStockId stockIdService;
    private final IGetStockValue stockValueService;
    private final IGetStockFutureValue futureService;

    public StockFacadeImpl() {
        // All services are local to the Facade (same server)
        this.stockIdService = new GetStockIdImpl();
        this.stockValueService = new GetStockValueImpl();
        this.futureService = new GetStockFutureValueImpl();
    }

    @Override
    public StockDetailsDTO getCompleteStockInfo(String stockName) {
        // 3 internal calls, 0 extra network round trips
        int id = stockIdService.getStockId(stockName);
        double value = stockValueService.getStockValue(id);
        double future = futureService.getFutureValue(id);
        return new StockDetailsDTO(stockName, id, value, future);
    }
}

// Client side: ONE call instead of THREE
StockDetailsDTO result = facade.getCompleteStockInfo("Reliance");

Message Facade Pattern

Synchronous vs Asynchronous Communication

When to use Message Facade

• If the client does not need the result immediately (e.g., sending email, generating PDF report)
• If the processing takes a long time (e.g., data migration, batch processing)
• If the system needs to handle spikes in traffic (message queue acts as buffer)
• If the external service may be temporarily unavailable (messages are persisted in queue)

// Message Facade: sends message to JMS queue
public class OrderMessageFacade {

    public void submitOrder(OrderDTO order) {
        // Create JMS message
        // Send to "orders" queue
        // Client is NOT blocked - returns immediately
        jmsTemplate.convertAndSend("orders-queue", order);
        System.out.println("Order submitted to queue. Processing async.");
    }
}

// Message Listener (processes asynchronously)
@JmsListener(destination = "orders-queue")
public void processOrder(OrderDTO order) {
    // This runs in a separate thread, later
    orderService.process(order);
    notificationService.sendConfirmation(order);
}

Note: "QUEUE" concept in messaging is used in JEE where sent message is consumed by one and only one receiver. In "TOPIC" concept, the message published by producer gets delivered to all the subscribers. This follows the publish-subscribe model.

JMS implementations and modern equivalents

• ActiveMQ, RabbitMQ (JMS implementations)
• Apache Kafka (distributed streaming, high throughput)
• AWS SQS/SNS (cloud-native message service)
• Spring JMS, Spring AMQP, Spring Cloud Stream (framework support)

Composite View Pattern

JSP - JavaServer Pages: each view comp is a separate JSP file.

angular/html - PA (pagination applied) to a single column of the DB table.

Composite/PV - PA (pagination applied) to multiple columns from multiple sections from the table together.

Problem: Monolithic Views

Solution: Composite View with Includes

View Layout Types

// main.jsp using Composite View pattern
<%-- Header: reusable across all pages --%>
<jsp:include page="header.jsp" />

<div class="layout">
    <%-- Sidebar: reusable navigation --%>
    <jsp:include page="sidebar.jsp" />

    <%-- Main content: page-specific --%>
    <div class="content">
        <jsp:include page="${contentPage}" />
    </div>
</div>

<%-- Footer: reusable across all pages --%>
<jsp:include page="footer.jsp" />

Each portion of web page that contains static content is called a tile. If the application has multiple pages which contains/need same set of tiles (like the Styles and Layout), tiles pools to avoid re-development/duplication of tiles.

Comparison Table

Session Facade, Message Facade, and Composite View Patterns

Three related JEE patterns | Synchronous vs Asynchronous Communication | Coarse-grained Service Access | Reusable View Components | Full Stock Trading and E-Commerce Examples | 12 Interview Questions

Session Facade Pattern

Problem: Multiple Network Round Trips

Here BusinessDelegate comp of Client App is having multiple round trips with multiple external comps which leads to performance issues (problem).

Solution: Session Facade Aggregates Calls

Implementation

// Session Facade interface
public interface IStockFacade {
    StockDetailsDTO getCompleteStockInfo(String stockName);
}

// Session Facade implementation: aggregates 3 services
public class StockFacadeImpl implements IStockFacade {
    private final IGetStockId stockIdService;
    private final IGetStockValue stockValueService;
    private final IGetStockFutureValue futureService;

    public StockFacadeImpl() {
        // All services are local to the Facade (same server)
        this.stockIdService = new GetStockIdImpl();
        this.stockValueService = new GetStockValueImpl();
        this.futureService = new GetStockFutureValueImpl();
    }

    @Override
    public StockDetailsDTO getCompleteStockInfo(String stockName) {
        // 3 internal calls, 0 extra network round trips
        int id = stockIdService.getStockId(stockName);
        double value = stockValueService.getStockValue(id);
        double future = futureService.getFutureValue(id);
        return new StockDetailsDTO(stockName, id, value, future);
    }
}

// Client side: ONE call instead of THREE
StockDetailsDTO result = facade.getCompleteStockInfo("Reliance");

Message Facade Pattern

Synchronous vs Asynchronous Communication

When to use Message Facade

• If the client does not need the result immediately (e.g., sending email, generating PDF report)
• If the processing takes a long time (e.g., data migration, batch processing)
• If the system needs to handle spikes in traffic (message queue acts as buffer)
• If the external service may be temporarily unavailable (messages are persisted in queue)

// Message Facade: sends message to JMS queue
public class OrderMessageFacade {

    public void submitOrder(OrderDTO order) {
        // Create JMS message
        // Send to "orders" queue
        // Client is NOT blocked - returns immediately
        jmsTemplate.convertAndSend("orders-queue", order);
        System.out.println("Order submitted to queue. Processing async.");
    }
}

// Message Listener (processes asynchronously)
@JmsListener(destination = "orders-queue")
public void processOrder(OrderDTO order) {
    // This runs in a separate thread, later
    orderService.process(order);
    notificationService.sendConfirmation(order);
}

Note: "QUEUE" concept in messaging is used in JEE where sent message is consumed by one and only one receiver. In "TOPIC" concept, the message published by producer gets delivered to all the subscribers. This follows the publish-subscribe model.

JMS implementations and modern equivalents

• ActiveMQ, RabbitMQ (JMS implementations)
• Apache Kafka (distributed streaming, high throughput)
• AWS SQS/SNS (cloud-native message service)
• Spring JMS, Spring AMQP, Spring Cloud Stream (framework support)

Composite View Pattern

JSP - JavaServer Pages: each view comp is a separate JSP file.

angular/html - PA (pagination applied) to a single column of the DB table.

Composite/PV - PA (pagination applied) to multiple columns from multiple sections from the table together.

Problem: Monolithic Views

Solution: Composite View with Includes

View Layout Types

// main.jsp using Composite View pattern
<%-- Header: reusable across all pages --%>
<jsp:include page="header.jsp" />

<div class="layout">
    <%-- Sidebar: reusable navigation --%>
    <jsp:include page="sidebar.jsp" />

    <%-- Main content: page-specific --%>
    <div class="content">
        <jsp:include page="${contentPage}" />
    </div>
</div>

<%-- Footer: reusable across all pages --%>
<jsp:include page="footer.jsp" />

Each portion of web page that contains static content is called a tile. If the application has multiple pages which contains/need same set of tiles (like the Styles and Layout), tiles pools to avoid re-development/duplication of tiles.

Comparison Table