Java Stream API, introduced in Java 8, revolutionized how developers process data collections. This functional-style approach makes code more readable. In this blog, we’ll dive into a real-world example to demonstrate the power and flexibility of the Java Stream API.

Before we get into the example, let’s briefly look at the core concepts of the Stream API:

Streams: Sequences of elements supporting sequential and parallel operations.
Intermediate Operations: Transform streams into another stream (e.g., map, filter).
Terminal Operations: Produce a result or side effect (e.g., collect, forEach).

Real-World Scenario: E-commerce Order Processing

Step 1: Setting Up the Data Models

public class Customer {
    private Long id;
    private String name;
    private String email;

//constructor,getters and setter, tostring
}

public class Order {
    private Long id;
    private LocalDate date;
    private Customer customer;
    private List<Product> products;
    private BigDecimal total;

//constructor,getters and setter, tostring
}

public class Product {
    private Long id;
    private String name;
    private BigDecimal price;

//constructor,getters and setter, tostring
}

Step 2: Let’s create some sample orders to work with.


public class SampleData {
    public static List<Order> getOrders() {
        Customer customer1 = new Customer(1L, "Alice Smith", "alice@example.com");
        Customer customer2 = new Customer(2L, "Bob Johnson", "bob@example.com");

        Product product1 = new Product(1L, "Laptop", new BigDecimal("1200.00"));
        Product product2 = new Product(2L, "Smartphone", new BigDecimal("800.00"));
        Product product3 = new Product(3L, "Tablet", new BigDecimal("600.00"));

        Order order1 = new Order(1L, LocalDate.now().minusDays(2), customer1, Arrays.asList(product1, product3), new BigDecimal("1800.00"));
        Order order2 = new Order(2L, LocalDate.now().minusDays(1), customer2, Arrays.asList(product2), new BigDecimal("800.00"));
        Order order3 = new Order(3L, LocalDate.now(), customer1, Arrays.asList(product1, product2, product3), new BigDecimal("2600.00"));

        return Arrays.asList(order1, order2, order3);
    }
}

Step 3: Let’s perform various operations on this data using the Stream API.

public class StreamExamples {

    //this method will return the total revenue of orders
    public static BigDecimal totalRevenue(List<Order> orders){

        BigDecimal totalRevenue = orders.stream()
                .map(Order::getTotal)
                .reduce(BigDecimal.ZERO, BigDecimal::add);
        return totalRevenue;
    }

    //this method will return the list of all products that were sold
    public static List<Product> getAllProductsSold(List<Order> orders){

        List<Product> productsSold = orders.stream()
                .flatMap(order -> order.getProducts().stream())
                .distinct()
                .toList();

        return productsSold;

    }
}

Conclusion

The examples above showcase just a few ways you can use the Stream API to handle common tasks in an e-commerce application. As you continue to explore, you’ll find even more opportunities to simplify and enhance your Java code with streams.

References

https://www.baeldung.com/java-8-streams

https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html

https://www.geeksforgeeks.org/stream-in-java/

GitHub : https://github.com/tharindu1998/StreamAPIBlogExample

Simplifying Data Processing with Java Stream API

Real-World Scenario: E-commerce Order Processing

Conclusion

References