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Tharindu Dulshan Fernando
Tharindu Dulshan Fernando

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Simplifying Data Processing with Java Stream API

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
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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", "");
        Customer customer2 = new Customer(2L, "Bob Johnson", "");

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

        return Arrays.asList(order1, order2, order3);
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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 =
                .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 =
                .flatMap(order -> order.getProducts().stream())

        return productsSold;

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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.


GitHub :

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