What are Microservices In Java?

How Do Microservices Work?

In a Java application built using microservices, a large monolithic system is broken down into smaller, independent units, each responsible for a specific business task. These services communicate with each other through APIs, enabling scalable, maintainable, and flexible software development.

1. Service Decomposition by Function

Each microservice focuses on a single functionality, such as user management, order processing, or inventory. In Java, this often involves separating logic into individual Spring Boot applications. This separation simplifies code, testing, and scaling for specific features without affecting the whole system.
 

2. Business-Specific Service Responsibility

Microservices are aligned with specific business capabilities. For example, a payment service handles all payment-related operations. This clear ownership makes services more understandable and maintainable. In Java, domain-driven design (DDD) principles often guide the creation of such business-aligned services.
 

3. Communication via APIs

Microservices communicate over the network using lightweight protocols like HTTP/REST or messaging queues. In Java, Spring Boot and Spring Cloud help build RESTful APIs and manage service discovery. This allows services to remain independent yet work together as a system.
 

4. Technology Flexibility

Each microservice can be built using different technologies best suited to its task. In a Java environment, while one service might use Spring Boot, another might use Quarkus or Micronaut. This flexibility ensures developers can choose tools optimized for each service.
 

5. Independent Deployment and Updates

Microservices can be deployed independently, meaning updates or bug fixes to one service don’t require changes to the entire application. Java-based services can be containerized using Docker and managed via orchestration tools like Kubernetes for smooth deployment and scaling.
 

This architecture improves agility, fault isolation, and team autonomy, making microservices a powerful approach for modern Java development.

Principles of Microservices

The “must-have” principles of a microservice are:

• Single Responsibility principle: The single responsibility principle states that a class should have a single reason to change. Any microservice cannot serve more than one responsibility at a time.
• Modelled around the business domain: Microservices in java never restricts themselves from accepting appropriate technology stack or database. The stack or database is most suitable for solving the business purpose.
• Isolate Failure: The large application can remain mostly unaffected by the failure of a single module. A service might fail at any time. So, it is important to detect failure quickly, if possible, automatically restore failure.
• Infrastructure automation: Infrastructure automation is the process of scripting environments. With the help of a scripting environment, we can apply the same configuration to a single node or thousands of nodes. It is also known as configuration management, scripted infrastructures, and system configuration management.
• Deploy independently: Microservices in Java are platform agnostic. It means we can design and deploy them independently without affecting the other services.

Main Components of Microservices Architecture

A successful microservices architecture depends on a combination of loosely coupled components that ensure independent service development, communication, deployment, and resilience. Below are the core elements that make microservices scalable, efficient, and robust—especially within Java-based systems.

1. Microservices

Each microservice is an independent unit responsible for a specific business functionality. In Java, microservices are commonly developed using frameworks like Spring Boot. These services run independently, can be deployed separately, and communicate via APIs, ensuring modularity and maintainability.
 

2. API Gateway

The API Gateway serves as a single entry point for client requests. It handles routing, load balancing, authentication, and request transformation. In Java ecosystems, Spring Cloud Gateway and Zuul (by Netflix) are popular tools used to implement this layer.
 

3. Service Registry and Discovery

This component keeps track of all active microservices and allows dynamic service registration and lookup. Java developers often use Spring Cloud Eureka or Consul for managing service discovery, enabling services to find each other without hardcoding endpoints.
 

4. Load Balancer

A load balancer distributes incoming traffic evenly across multiple instances of a service to ensure high availability and fault tolerance. Tools like Netflix Ribbon or Spring Cloud LoadBalancer are frequently used in Java microservices setups.
 

5. Containerization

Microservices are often packaged into containers for consistent deployment. Tools like Docker allow each Java service to run with its own dependencies. Containers ensure uniformity across environments and simplify scaling and orchestration with platforms like Kubernetes.
 

6. Event Bus / Message Broker

Microservices often use asynchronous communication to stay decoupled. Message brokers like Apache Kafka, RabbitMQ, or ActiveMQ are commonly used in Java applications to transmit events between services using publish/subscribe or message queues.
 

7. Database per Microservice

Each microservice manages its own database to avoid tight coupling at the data layer. This enables teams to choose the most suitable database technology per service, such as using MySQL, MongoDB, or PostgreSQL, managed independently from other services.
 

8. Caching

Caching enhances performance by storing frequently accessed data in memory. Tools like Ehcache, Caffeine, or Redis (via Spring Cache abstraction) are used in Java microservices to reduce database load and improve response times.
 

9. Fault Tolerance and Resilience Components

To handle service failures gracefully, microservices use resilience patterns like circuit breakers, retries, and fallbacks. In Java, Resilience4j or Netflix Hystrix are used to implement these mechanisms, ensuring that one service failure doesn’t crash the entire system.

These components together form the backbone of a robust microservices architecture, enabling scalable, maintainable, and resilient Java applications.

Benefits of Microservices in Java

We have a vast number of applications and benefits of Microservices which are the best practices, few are:

• Smaller Modules: The application is broken into smaller modules that are easy for developers to code and maintain.
• Easier Process Adaption: By using microservices in java, new Technology & Process adaption becomes easier. You can try new technologies with the latest microservices that we use.
• Independent scaling: Each microservice can scale independently via X-axis scaling (cloning with more CPU or memory) and Z-axis scaling (sharding), based upon their requirements.
• Unaffected: Large applications remain unaffected by the failure of a single module.
• DURS: Each service can be independently DURS (deployed, updated, replaced, and scaled).

Restrictions of Microservices

• Configuration Management: As it becomes granular, the headache comes from configuring the services and monitoring those. You need to maintain configurations for hundreds of components across environments.
• Debugging: Tracking down the service failure is a meticulous job. You might need to look into multiple services across different components. Centralised Logging and Dashboards are essential to make it easy to debug problems.
• Automation: As there are several smaller components instead of a monolith, you need to automate everything – Builds, Deployment, Monitoring, etc.
• Testing: It needs a greater effort from end to end. In addition, you are testing, as it needs all the dependent services to be up and running.

So far, end-to-end, we have seen the benefits, principles, and restrictions of microservices. Let’s design some applications now.

Microservice frameworks in Java

Several microservices in java, frameworks can be used for deploying Java. Some of them are:

• Spring Boot: This is probably the best microservices in the Java framework that works on top languages for Inversion of Control, Aspect-Oriented Programming, etc.
• Drop wizard: Dropwizard pulls together stable, mature libraries from the Java ecosystem into a simple, lightweight package that lets you focus on getting things done.
• Restlet: Restlet Framework helps Java developers build better web APIs that follow the REST architecture style.
• Jersey: This open-source framework supports JAX-RS APIs in Java and is very easy to use.
• Swagger: Helps you in documenting API and gives you a development portal, which allows users to test your APIs.
• Spark: A micro-framework for creating web applications in Kotlin and Java 8 with minimal effort.

We also have many frameworks like Ninja Web Framework, Play Framework, RestExpress, etc.

How to create using Dropwizard?

DropWizard pulls together mature and stable Java libraries in lightweight packages that you can use for your applications. It uses Jetty for HTTP, Jersey for REST, and Jackson for JSON, along with Metrics, Guava, Logback, Hibernate Validator, Apache HttpClient, Liquibase, Mustache, Joda Time, and Freemarker.

You can also check the documentation here.

Let’s explore a sample code.

<properties>

<dropwizard.version>LATEST VERSION</dropwizard.version>

</properties>

Then list the dropwizard-core library:

<dependencies>

<dependency>

<groupId>io.dropwizard</groupId>

<artifactId>dropwizard-core</artifactId>

<version>${version}</version>

</dependency>

</dependencies>

The above code will set up a Maven project for you. From here, you can create a configuration class, an application class, a representation class, a resource class, or a health check, and you can also build Fat JARS and then run your application.

Microservices with Spring Boot

Spring Boot gives you a Java application to use with your apps via an embedded server. It uses Tomcat, so you do not have to use Java EE containers. 

You can find the Spring Boot projects here, and you will realize that Spring Boot has all the infrastructures that your applications need.

Sample code:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
@RestController
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
    @GetMapping("/hello")
    public String hello(@RequestParam(value = "name", defaultValue = "World") String name) {
        return String.format("Hello %s!", name);
    }
}

The hello() method is designed to take a String parameter called name and then combine this parameter with the word “Hello” in the code. This means that if you set your name to “Amy” in the request, the response would be “Hello Amy.”

The @RestController annotation tells Spring that this code describes an endpoint that should be made available over the web. 

The @GetMapping(“/hello”) tells Spring to use the hello() method to answer requests that are sent to the http://localhost:8080/hello address. 

Finally, the @RequestParam is telling Spring to expect a name-value in the request, but it will use the word “World” by default if it’s not there.

You can try it on windows using the command: “mvnw spring-boot:run” and for Linux: “./mvnw spring-boot:run.”

Jersey

Jersey RESTful framework is open source, and it is based on JAX-RS specification. Jersey’s applications can extend existing JAX-RS implementations and add features and utilities that would make RESTful services simpler and make client development easier.

The best thing about Jersey is its exceptional documentation. It’s filled with excellent examples. Jersey is also fast and has extremely easy routing.

A sample code that you can try:

package org.glassfish.jersey.examples.helloworld;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
@Path("helloworld")
public class HelloWorldResource {
    public static final String CLICHED_MESSAGE = "Hello World!";

 @GET
    @Produces("text/plain")
    public String getHello() {
        return CLICHED_MESSAGE;
    }
}

The above code prints a Hello World message. Jersey is very easy to use with other libraries, such as Netty or Grizzly, supporting asynchronous connections. It does not need servlet containers. It does, however, have an unpolished dependency injection implementation.

Play Framework

It gives you an easier way to build, create, and deploy Web applications using Scala and Java. This framework is ideal for a RESTful application that requires you to handle remote calls in parallel. It is also very modular and supports async. Play Framework also has one of the biggest communities out of all microservices frameworks.

Sample code you can try:

package controllers;
import play.mvc.*;
public class Application extends Controller {
    public static void index() {
        render();
    }

    public static void sayHello(String myName) {
        render(myName);
    }
}

Restlet

Restlet helps developers create fast and scalable Web APIs that adhere to the RESTful architecture pattern. It has good routing and filtering and is available for Java SE/EE, OSGi, Google AppEngine (part of Google Compute), Android, and other major platforms.

Restlet comes with a steep learning curve that is made worse by a closed community, but you can probably get help from people at StackOverflow.

Sample code:

package firstSteps;
import org.restlet.resource.Get;
import org.restlet.resource.ServerResource;
/** 
 * Resource which has only one representation. 
 */
public class HelloWorldResource extends ServerResource {
    @Get
    public String represent() {
        return "hello, world";
    }
}

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Real-World Example of Microservices: Amazon

Amazon, a global e-commerce leader, efficiently handles millions of transactions daily through a robust microservices architecture. Each functional component is isolated into individual services that work independently but collaborate seamlessly to deliver a fast, reliable, and scalable shopping experience.

1. User Service

Manages user accounts, authentication, and profiles. It verifies credentials during login and interacts with services like Wishlist and Cart. Java developers often implement it with Spring Security for authentication and JWT tokens for session management.
 

2. Search Service

Handles all product search queries. It indexes catalog data and returns relevant search results. It interacts heavily with the Catalog Service and uses search engines like Elasticsearch integrated via REST APIs built with Spring Boot.
 

3. Catalog Service

Stores detailed product information such as names, prices, and descriptions. It supplies data to the Search and Recommendation Services and is typically backed by a scalable NoSQL database like MongoDB.
 

4. Cart Service

Maintains user shopping carts and allows real-time updates. It interacts with the User Service for cart ownership and Catalog Service for product verification. This service is usually stateless and session-aware.
 

5. Wishlist Service

Allows users to save items for future purchases. It communicates with the User and Catalog Services. Developers use persistent storage like PostgreSQL and secure APIs via Spring Boot.
 

6. Order Taking Service

Receives order requests and forwards them to the Order Processing Service. It ensures data validation and transactional integrity. It often uses RESTful APIs and Spring MVC.
 

7. Order Processing Service

Handles order validation, inventory checks, and confirmation. It communicates with the Warehouse, Payment, and Logistics Services. Developers often integrate this service with message brokers like Kafka for asynchronous processing.
 

8. Payment Service

Processes user payments securely. It supports multiple gateways and integrates with Order and Notification Services. Java developers implement this using Spring Boot and secure APIs with OAuth2.
 

9. Logistics Service

Manages shipping and delivery status. It coordinates with Warehouse and Order Processing Services. Uses REST APIs and geolocation services, often built using Spring Cloud.
 

10. Warehouse Service

Monitors stock levels and inventory movements. It provides data to Order Processing and Logistics Services. Java-based microservices use JPA with databases like MySQL for managing inventory data.
 

11. Notification Service

Sends emails, SMS, or push notifications for order updates and promotions. It interacts with User and Order Services and is implemented with asynchronous messaging tools like RabbitMQ or Kafka.
 

12. Recommendation Service

Offers product suggestions based on user behavior and purchase history. It uses AI/ML models and communicates with Catalog and User Services. Commonly built using Spring Boot and integrated with data analytics tools.

Service-Oriented Architecture (SOA) vs. Microservices Architecture

Microservices provide greater flexibility, scalability, and independence, making them a better fit for modern Java applications, especially when using tools like Spring Boot and Spring Cloud.

Benefits and Challenges of Using Microservices Architecture

Benefits of Using Microservices Architecture

• Scalability:
  Each service can be scaled independently based on demand. Java microservices using Docker and Kubernetes allow efficient scaling.
   
• Faster Development:
  Teams can develop and deploy services independently, accelerating delivery cycles and updates.
   
• Technology Flexibility:
  Developers can choose the best technology stack for each service, e.g., Java with Spring Boot for APIs and Python for ML services.
   
• Fault Isolation:
  If one microservice fails, it doesn’t affect the entire system. Tools like Resilience4j help implement fault tolerance.
   
• Continuous Deployment:
  Easier to deploy and rollback individual services, allowing continuous integration and delivery pipelines.
   
• Better Organization:
  Services map closely to business functions, enhancing code clarity and ownership among teams.

Challenges of Using Microservices Architecture

• Complexity in Management:
  Managing multiple services, their communication, and deployments increases operational complexity.
   
• Distributed System Issues:
  Network latency, data consistency, and error handling become more complex in distributed environments.
   
• Data Management:
  Ensuring consistency across databases used by different services is challenging and may require event-driven patterns.
   
• Monitoring and Debugging:
  Tracing issues across several microservices needs sophisticated tools like ELK Stack or Zipkin for observability.
   

Microservices offer excellent scalability and agility for Java applications but require careful architectural planning and robust tooling to manage complexity effectively.

Frequently Asked Questions

What are Microservices in Java?

Microservices are a form of service-oriented architecture style (one of the most important skills for Java developers) wherein applications are built to collect different smaller services rather than one whole app.

Is Java good for Microservices?

Java is great for writing microservices. Among other reasons, its annotation syntax is easy to read. Java annotations make writing microservices much easier, especially when powered by a framework like Spring Boot. There’s a lot of value in readability, especially when it comes to working on complex systems.

Is spring boot a Microservice?

Spring Boot is an open-source framework based on the Java platform to create excellent microservices. It can help you build spring applications that can be used in the applications and are production-ready.

Is Docker a Microservice?

Since you have microservices architecture, you can now encapsulate each of them in Docker containers. Docker containers are lightweight, resource isolated environments through which you can build, maintain, ship, and deploy your application.

Conclusion

Microservices architecture divides large applications into smaller, independent services that handle specific business functions. These services communicate via APIs and are easier to deploy, scale, and maintain. In Java, frameworks like Spring Boot and Spring Cloud make building and managing microservices more efficient. Key components such as service registries, API gateways, and message brokers ensure smooth interaction between services. Amazon’s use of microservices shows how this approach supports high performance and flexibility. While microservices offer many benefits, they also introduce challenges like service coordination and data consistency. Still, their future in Java development looks promising as demand for scalable solutions grows.