Lecture 172: How Spring Boot helps you build microservices fast

Today we dive into the tools and features of Spring Boot that make developers' lives easier — from auto-configuration to embedded servers and container integration. So buckle up, we're jumping into the world of fast microservice development!

Spring Boot Starters: How to avoid writing miles of setup

Imagine you start a new project and add dozens of dependencies manually. Tedious, right? Spring Boot Starters are like a "magic wand" that does it for you. For example:

• Want to work with REST APIs? Add spring-boot-starter-web, and all required dependencies will be wired in automatically.
• Need database support? Just use spring-boot-starter-data-jpa, and Hibernate, JPA, and other tools will be configured.

Example pom.xml using starters for REST API and database:

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
</dependencies>

Auto-configuration: goodbye manual setup

Spring Boot detects which dependencies are on your classpath and configures them for you. That's called auto-configuration. For example:

• If you have spring-boot-starter-web, Spring Boot will automatically set up an embedded server (Tomcat) and configure the basic settings for a REST API.
• If you add a database dependency, Spring Boot will create an EntityManager or JdbcTemplate and wire them up.

Example of automatic database configuration:

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    username: sa
    password:
  jpa:
    hibernate:
      ddl-auto: update

All you need to do is put the params into application.yml or application.properties. Spring Boot will take care of the rest!

Embedded servers: works out of the box

Spring Boot ships with embedded servers like Tomcat, Jetty, or Undertow. That means you don't have to deal with external servlet containers. Your app becomes self-contained:

• Build a jar.
• Run it with java -jar.
• Your app is ready to serve requests.

Benefits of embedded servers:

• Environment independence.
• Easy deployment.
• CI/CD friendliness.

DevOps and CI/CD support

Ready for containers

Spring Boot plays nicely with Docker and Kubernetes. Because apps are compact and easy to deploy, Spring Boot applications are straightforward to package into Docker images. Here's a simple Dockerfile example:

FROM openjdk:11-jre
COPY target/myapp-0.1.0.jar app.jar
ENTRYPOINT ["java", "-jar", "app.jar"]

This way, microservices become independent and easy to scale in the cloud.

Built-in testing support

Don't forget testing — the foundation of any reliable app. Spring Boot gives you handy tools like:

• Spring Boot Test — for integration testing.
• MockMvc — for testing REST controllers without starting a server.

Example controller test with MockMvc:

@SpringBootTest
@AutoConfigureMockMvc
public class MyControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @Test
    public void testGetEndpoint() throws Exception {
        mockMvc.perform(get("/api/example"))
                .andExpect(status().isOk())
                .andExpect(content().string("Hello World!"));
    }
}

Benefits of using Spring Boot

1. Faster than you can say "Hello World". With Spring Boot you can spin up and deploy a working microservice in minutes. This is especially handy for startups and small projects where development speed matters.
2. Flexibility and scalability. Spring Boot fits both small apps and large scalable systems. You can start as a monolith and move to microservices later with ease.
3. Easy on-ramp. If you know Java and basic Spring concepts, getting started with Spring Boot is like learning to ride a bike with a motor.

Example: creating a microservice with a REST API

Let's see how quickly you can get a Spring Boot app up and running.

Step 1: project setup

1. Go to Spring Initializr.
2. Set the params:
   • Dependency: Spring Web.
   • Language: Java.
   • Build System: Maven or Gradle.
3. Download the project and open it in your IDE.

Step 2: implement the controller

@RestController
@RequestMapping("/api/customers")
public class CustomerController {

    @GetMapping
    public String getAllCustomers() {
        return "List of customers";
    }

    @PostMapping
    public String createCustomer() {
        return "Customer created";
    }
}

Step 3: add configuration

In application.yml add basic config:

server:
  port: 8081
logging:
  level:
    root: INFO
spring:
  application:
    name: customer-service

Step 4: run and verify

Start the app with mvn spring-boot:run or run the main() method. Check the /api/customers endpoint.

Tips and gotchas

1. Don't overcomplicate auto-configuration. Just because something works out of the box doesn't mean you can't override the defaults.
2. Keep an eye on dependencies. Too many Starters can lead to bloated dependency trees.
3. Optimize container sizes. Use base images like alpine to shrink Docker images.

Spring Boot makes microservice development pleasant and fast. It helps you focus on business logic instead of wasting time on configuration boilerplate. The next step — build your first microservice and set up how it talks to other parts of the system.