Microservices in Java: A Roadmap for Beginners

Microservices in Java: Don't Be Afraid, It's Easier Than It Seems

Have you ever looked at a monolithic application and thought: "I wish I could split this into parts so that one change doesn't break everything"? Congratulations — you're ready for microservices. In the Java world, this topic is surrounded by myths of incredible complexity and a ton of technologies. In reality, you can start with two classes and one application.yml file.

In this article, we won't build a spaceship. We'll write two simple microservices that talk to each other via HTTP, and we'll figure out where to actually start. No magic — just Java, Spring Boot, and common sense.

What is a Microservice (In Simple Terms)

Imagine a restaurant. A monolith is when one chef does everything: cooks soup, grills steak, and washes dishes. Microservices are a team: one chef is responsible only for soups, another for meat, a third for desserts. Each works independently, but together they create a shared menu.

In Java, a microservice is an independent application responsible for one business function (e.g., "User Management" or "Order Processing"). It has its own database, its own code, and communicates with other services over the network (usually via HTTP/REST or message brokers).

Where to Start: A Gentleman's Toolkit

For your first project, you'll need just three things:

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• Java 17+ — a modern version with useful features (records, sealed classes).
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• Spring Boot 3.x — the most popular framework for microservices in Java. It handles 80% of the routine work.
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• Maven or Gradle — for building. Maven is simpler to start with, Gradle is faster.
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Additionally, when you want to make things more complex:

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• Docker — to package the service into a container.
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• Spring Cloud — for service discovery and load balancing.
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• PostgreSQL/H2 — a database of your choice.
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Tip: Don't try to learn Kubernetes and Kafka right away. Start with simple REST communication.

Writing Your First Microservice: User Service

Let's create a simple microservice that can return information about users. Use Spring Initializr (start.spring.io) or create the project manually.

Add dependencies to pom.xml:

<dependency>\n    <groupId>org.springframework.boot</groupId>\n    <artifactId>spring-boot-starter-web</artifactId>\n</dependency>\n\n<dependency>\n    <groupId>org.springframework.boot</groupId>\n    <artifactId>spring-boot-starter-data-jpa</artifactId>\n</dependency>\n\n<dependency>\n    <groupId>com.h2database</groupId>\n    <artifactId>h2</artifactId>\n    <scope>runtime</scope>\n</dependency>

Now let's write the user model:

import jakarta.persistence.*;\n\n@Entity\n@Table(name = "users")\npublic class User {\n    @Id\n    @GeneratedValue(strategy = GenerationType.IDENTITY)\n    private Long id;\n    private String name;\n    private String email;\n\n    // constructors, getters, setters (Lombok can be used)\n    public User() {}\n\n    public User(String name, String email) {\n        this.name = name;\n        this.email = email;\n    }\n\n    // getters and setters\n}

Repository (simplified data access):

import org.springframework.data.jpa.repository.JpaRepository;\n\npublic interface UserRepository extends JpaRepository<User, Long> {\n}

And the controller — a REST endpoint:

import org.springframework.web.bind.annotation.*;\n\nimport java.util.List;\n\n@RestController\n@RequestMapping("/api/users")\npublic class UserController {\n\n    private