A Java Microservices Overview

In the last decade, microservices have changed how developers and organizations build and ship applications. According to Stack Overflow’s 2023 Developer Survey, nearly 49% of software professionals use microservices daily. To further understand how microservices have risen in popularity, we’ll look at the Java landscape and explore how and when you should build and ship microservices using Java.

What are Microservices in Java?

Microservices are a system architectural pattern that allows developers to build and deploy applications modularly. A modular architecture means one service can be changed and deployed independently from the rest of the system’s services. Each microservice is designed to perform a specific business function and can be developed, deployed, and scaled separately.

Microservices in Java let programmers use Java to build and ship small and large services using features provided by the Java virtual machine (JVM) and Java ecosystem.

How Do Java Microservices Work?

Java microservices function as separate, self-contained components that work together to fulfill a particular application’s requirements. This separation of concern makes each microservice responsible for a single business capability and communicates with other microservices and external systems through well-defined interfaces.

How Do Microservices Communicate with Each Other in Java?

Java microservices can communicate with each other primarily through existing web protocols such as HTTP/REST, messaging queues, pub/sub systems like RabbitMQ or Apache Kafka, or even newer communication protocols like GraphQL and gRPC. The choice of communication method depends on factors like performance requirements, scalability, and application complexity. Many microservices architectures use a combination of these approaches to communicate within the system.

Java Microservices vs. Monolith

Here are some of the major differences between using a microservices architecture and a monolithic architecture:

- Scalability: Microservices offer better scalability because each service can be scaled independently as the product’s active users grow. However, scaling a monolithic application typically involves scaling the entire application, even if only specific modules require additional resources.
- Maintainability and Development: Microservices enable smaller, focused development teams to work independently on different services. Each team can set clear boundaries between services, resulting in faster development cycles and easier debugging and testing of individual services. On monolithic architectures, applications can become complex and challenging to maintain as they grow in size and functionality. In the initial stages of your product, it’s a good bet to have a monolith system and adapt to microservices as your organization grows.
- Resilience: Microservices are more resilient to failures, as issues in one service don’t necessarily affect the entire application. With monoliths, a single point of failure in an application can bring down the entire system. In these cases, relying on fault-tolerance mechanisms while writing Java applications is ideal.

Is Java Good for Microservices?

Java is ideal for building microservices due to its extensive libraries, performance optimizations, and vast ecosystem. We’ll expand on why below:

- Extensive Libraries: Libraries like Spring Cloud Netflix provide essential components for building distributed systems, including service discovery (Eureka), fault tolerance (Hystrix), and client-side load balancing (Ribbon). These libraries integrate seamlessly with Java applications, enabling developers to implement resilient and scalable microservices architectures. A few other Java microservices widely used by developers are Spring Boot, Jersey, Dropwizard, and Spark.
- Performance Optimizations: JVM has evolved significantly to support microservices architecture. With innovations like GraalVM and improvements in JVM runtime, Java applications can achieve better performance and efficiency, which is crucial for microservices handling high-throughput and low-latency requirements. Additionally, Java’s multithreading capabilities allow developers to efficiently handle concurrent requests, a common requirement in microservices.

Some large user-facing products are proof of Java’s suitability for microservices. For example:

- Netflix: Netflix extensively uses Java for its microservices’ architecture, leveraging libraries like Hystrix and RxJava to ensure fault tolerance and load balancing.
- Uber: Uber’s backend services are predominantly built using Java, showcasing its capability to handle large-scale distributed systems.
- Amazon: Amazon’s AWS Lambda, a serverless compute service, supports Java as a runtime environment, demonstrating Java’s adaptability to modern cloud-native architectures.

Use Cases for Java Microservices

1. Real-Time Analytics: Microservices can process large amounts of data in real time, making them ideal for applications that require rapid data analysis.
2. User Authentication: A separate service in your system can handle user authentication and authorization, allowing other services to focus on their core functionalities.
3. Inventory Management: Microservices can manage inventory levels across multiple stores or warehouses, allowing for greater scalability and flexibility.
4. IoT Applications: Where numerous devices generate large volumes of data, Java microservices can handle data processing, device management, and real-time analytics.

Java Microservices Tutorial

Let’s look at how to use Java to start a simple “Hello World” microservice using the Gradle build tool.

Step 1: Set Up the Project Repo or Directory

If you’re on your workstation, create an empty directory to host the sample service. We recommend creating a private GitHub repository by visiting repo.new in your web browser. Once you do that, start a GitHub codespace on the newly created repository.

Step 2: Initialize a Gradle Project

Once you’re inside the code workspace, run the following commands to verify that Java and Gradle are installed in the terminal:

java --version
gradle –version

1 2	java --version gradle –version

Use the following command to create a Java project using Gradle:

gradle init --type java-application

1	gradle init --type java-application

Step 3: Implement App class

Let’s create a simple HTTP server using HttpServer.

Create a new directory (src/main/java) if it doesn’t exist, and then create a Java package directory structure (com.example.microservice) inside src/main/java. After this, create a Java source file named App.java inside the package directory.

package org.example;


import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpExchange;
import java.io.IOException;
import java.io.OutputStream;

public class App {
    public static void main(String[] args) throws IOException {
        int port = 8080;
        HttpServer server = HttpServer.create(new java.net.InetSocketAddress(port), 0);

        server.createContext("/hello", new HelloHandler());
        server.setExecutor(null); // default executor

        System.out.println("Server started on port " + port);
        server.start();
    }

    static class HelloHandler implements HttpHandler {
        @Override
        public void handle(HttpExchange exchange) throws IOException {
            String response = "Hello from Microservice!";
            exchange.sendResponseHeaders(200, response.getBytes().length);
            OutputStream os = exchange.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }
}

package org.example;

import com.sun.net.httpserver.HttpServer;

import com.sun.net.httpserver.HttpHandler;

import com.sun.net.httpserver.HttpExchange;

import java.io.IOException;

import java.io.OutputStream;

public class App {

public static void main(String[] args) throws IOException {

int port = 8080;

HttpServer server = HttpServer.create(new java.net.InetSocketAddress(port), 0);

server.createContext("/hello", new HelloHandler());

server.setExecutor(null); // default executor

System.out.println("Server started on port " + port);

server.start();

}

static class HelloHandler implements HttpHandler {

@Override

public void handle(HttpExchange exchange) throws IOException {

String response = "Hello from Microservice!";

exchange.sendResponseHeaders(200, response.getBytes().length);

OutputStream os = exchange.getResponseBody();

os.write(response.getBytes());

os.close();

}

The HttpServer listens for incoming HTTP requests and delegates handling to the HelloHandler, which sends back a simple response. You can extend this example to handle more endpoints and more complex request/response logic based on your requirements.

Step 4: Test the Microservice

To start the microservice, use the gradle run command. Next, open a web browser or use a tool like cURL to test your microservice by accessing http://localhost:8080/hello. You should see the response: Hello from Microservice!

Conclusion

In this blog post, we explored how microservices can be the right solution architecture to use when the needs of your web application become more complex with additional users and time. We also looked at Java’s place in this landscape and stated its use cases in the cloud-native world. Lastly, we reviewed how to build a basic Java microservice using only standard Java HTTP server capabilities (HttpServer and HttpHandler) without using an external web framework.

To continue learning about microservices, review these resources from Couchbase:

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