Micronaut

Micronaut is a modern, JVM-based (Java Virtual Machine) full-stack framework for building modular, easily testable microservices and serverless applications. It’s designed to be lightweight, low-memory-footprint, and provide fast startup times. Micronaut is particularly well-suited for cloud-native and serverless architectures. Here are some key features and aspects of Micronaut:

Key Features: §

1. Low Overhead:

   • Micronaut is designed to have minimal runtime overhead. It achieves this by avoiding the use of reflection at runtime and by leveraging compile-time processing for dependency injection.

2. Compile-Time Dependency Injection:

   • Micronaut performs dependency injection at compile time, resulting in faster startup times and better runtime performance compared to frameworks that use runtime reflection.

3. Built-in Support for Cloud-Native Features:

   • Micronaut has built-in support for common cloud-native features such as service discovery, distributed configuration, and load balancing.

4. Serverless Support:

   • Micronaut is well-suited for serverless architectures. It provides features such as minimal cold starts, low memory usage, and efficient execution in serverless environments.

5. Reactive Programming:

   • Micronaut supports reactive programming with built-in support for reactive streams, allowing developers to build responsive and scalable applications.

6. Language Agnostic:

   • While Micronaut is often associated with the Java language, it is designed to be polyglot. It supports other languages on the JVM, such as Kotlin and Groovy, allowing developers to choose the language that best fits their needs.

7. Testing Support:

   • Micronaut is designed with testing in mind. It provides testing utilities and features that make it easy to write unit tests, integration tests, and perform end-to-end testing of Micronaut applications.

8. Modular Structure:

   • Micronaut encourages a modular and organized code structure. It allows developers to create modular applications with a clear separation of concerns.

9. Built-in Security:

   • Micronaut provides built-in security features, including support for JWT (JSON Web Tokens) and role-based access control.

Micronaut Projects: §

• Micronaut Core: The core framework for building microservices.

• Micronaut Data: Simplifies data access by providing a data-centric programming model.

• Micronaut Security: Provides security features and tools for securing Micronaut applications.

• Micronaut Test: A testing library that facilitates unit and integration testing of Micronaut applications.

• Micronaut GraphQL: Adds support for building GraphQL APIs in Micronaut applications.

• Micronaut AWS: Provides integrations with various Amazon Web Services (AWS) components.

• Micronaut for Spring: Allows developers to migrate Spring applications to Micronaut incrementally.

Getting Started: §

To get started with Micronaut, you typically use the Micronaut CLI (Command-Line Interface) or use Micronaut starters with build tools like Maven or Gradle. Micronaut applications can be built and run using popular IDEs such as IntelliJ IDEA or Eclipse.

Here is a basic example of a Micronaut application:

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
 
@Controller("/hello")
public class HelloController {
 
    @Get
    public String index() {
        return "Hello, Micronaut!";
    }
}

This simple controller responds to HTTP GET requests at the “/hello” endpoint.

---

A simple Micronaut Application §

import io.micronaut.http.annotation.Controller  
import io.micronaut.http.annotation.Get
 
@Controller("/hello")
class HelloController {
	@Get
	fun index(): String {
		return "hi"
	}
}

A JUnit test for the above,

package com.nish  
  
import io.micronaut.http.HttpRequest  
import io.micronaut.http.client.HttpClient  
import io.micronaut.http.client.annotation.Client  
import io.micronaut.test.extensions.junit5.annotation.MicronautTest  
import org.junit.jupiter.api.Assertions.assertEquals  
import org.junit.jupiter.api.Assertions.assertNotNull  
import org.junit.jupiter.api.Test  
  
@MicronautTest  
class HelloControllerTest (@Client("/") val client: HttpClient){  
  
    @Test  
    fun testHello() {  
        val request: HttpRequest<Any> = HttpRequest.GET("/hello")          
        val response = client.toBlocking().retrieve(request)  
        
        assertNotNull(response)  
        assertEquals(response, "hi")  
    }  
}

toBlocking refers to a synchronous (blocking) request

---

Changing content-type and status code in response §

@Controller("/hello")  
class HelloController {  
    
    @Get  
    @Produces(MediaType.TEXT_PLAIN) // Sets content type to text/plain  
    @Status(HttpStatus.ACCEPTED) // Sets status code to 202
    fun index (): String {  
        return "hi"  
    }  
}

Updated JUnit test,

// status code
assertEquals(response.status, HttpStatus.ACCEPTED)
 
// content-type
 

---

Refs §

1. https://guides.micronaut.io/latest/creating-your-first-micronaut-app-gradle-kotlin.html