Microservices in Java - A Detailed Guide

Microservices is an architectural style where an application is built as a collection of small, independent services, each responsible for a specific business capability. In Java, this style is commonly implemented using frameworks like Spring Boot.

Core Principles of Microservices

• Each service is independently deployable and owns its own data
• Services communicate over lightweight protocols, typically REST or messaging queues
• Services are organized around business capabilities rather than technical layers
• Each service can be developed, scaled, and deployed independently of the others

Simple REST Endpoint Example

@RestController
@RequestMapping("/orders")
public class OrderController {

    @GetMapping("/{id}")
    public Order getOrder(@PathVariable Long id) {
        return orderService.findById(id);
    }
}

Common Building Blocks

• API Gateway — a single entry point that routes requests to the right service
• Service Discovery — lets services find each other dynamically without hardcoded addresses
• Config Server — centralizes configuration across services
• Circuit Breaker — prevents a failing service from cascading failures across the system

Monolith vs Microservices

• A monolith is a single deployable unit; microservices are many independently deployable units
• Monoliths are simpler to build initially; microservices scale better for large, complex applications
• Microservices introduce network communication and distributed system challenges that monoliths don't have