Web Applications with Grails and Micronaut

Two frameworks let you build web applications and services in Groovy.

Grails

Grails is a full-stack web framework built on Spring Boot, now an Apache project. It follows "convention over configuration", inspired by Ruby on Rails: put a class in the right folder and Grails knows what it is.

// illustrative — grails-app/domain/shop/Book.groovy
package shop

class Book {
    String title
    String author
    BigDecimal price
    Date dateCreated

    static constraints = {
        title blank: false, maxSize: 200
        price min: 0.0
    }
}

// illustrative — grails-app/controllers/shop/BookController.groovy
package shop

class BookController {
    static responseFormats = ['json']

    def index(Integer max) {
        respond Book.list(max: Math.min(max ?: 10, 100), sort: 'title')
    }

    def show(Long id) {
        respond Book.get(id)
    }

    def byAuthor(String author) {
        respond Book.findAllByAuthorIlike("%${author}%")
    }
}

• Domain classes are persisted with GORM (Grails' data layer, on Hibernate or MongoDB). Methods like list, get, save, and dynamic finders such as findAllByAuthorIlike are added at runtime — the metaprogramming from Level 3's first lesson.
• static constraints is a DSL for validation rules.
• Controllers map to URLs by convention (/book/show/1) or through UrlMappings.
• Commands: grails create-app, grails create-domain-class, ./gradlew bootRun. Grails apps are tested with Spock.

Micronaut

Micronaut is a JVM framework for microservices and serverless functions that supports Java, Kotlin, and Groovy. Instead of runtime reflection, it does dependency injection and routing at compile time (using AST transformations in Groovy), so apps start fast and use little memory.

// illustrative — src/main/groovy/shop/GreetingController.groovy
package shop

import groovy.transform.CompileStatic
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import jakarta.inject.Singleton

@Singleton
class GreetingService {
    String greet(String name) { "Hello, $name!" }
}

@CompileStatic
@Controller('/greet')
class GreetingController {
    private final GreetingService service
    GreetingController(GreetingService service) { this.service = service }

    @Get('/{name}')
    Map<String, String> greet(String name) {
        [message: service.greet(name)]
    }
}

$ curl http://localhost:8080/greet/Ada
{"message":"Hello, Ada!"}

Create projects at micronaut.io/launch (choose Groovy as the language) or with the mn CLI.

Which to choose

Spring Boot itself also works with Groovy classes if your team already uses Spring.