devnexus-2019-grails-micronaut.md

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[FIT] GRAILS 4 AND MICRONAUT

Getting the best out of Grails 4 and Micronaut

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About Me

• Graeme Rocher
• Creator of Grails and Micronaut
• Principal Engineer at Object Computing
• Oracle Groundbreaker Award Winner

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Agenda

• Introduction to Micronaut
• Introduction to Grails 4
• Grails vs Micronaut
• Using Micronaut Features in Grails
• Demos

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Micronaut for Grails Developers

• Micronaut a Foundational Library for building applications of any type
• Focuses on Small Memory Footprint and Speed
• Eliminates Reflection, Runtime Proxies and Runtime Analysis

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Why Micronaut?

• Micronaut is uses no reflection, no runtime proxies, no runtime byte code generation etc.
• Eliminating these leads to reduced memory consumption and faster startup
• Increasingly important for Microservices, Serverless, IoT, any low-memory footprint environment

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Micronaut vs Grails

Micronaut	Grails
Range of Runtimes	Servlet Only
General Purpose	Traditional Servlet Web Apps
DI, AOP etc.	Spring for DI, AOP etc.
Java, Kotlin, Groovy, GraalVM	Groovy Only
Client and Server	Server Only

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Grails 4 and Micronaut

• Micronaut the Parent ApplicationContext
• Made possible by
  • http://github.com/micronaut-projects/micronaut-spring
• Micronaut Libraries become usable in Grails
• Anything we build for Micronaut benefits Grails

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What Can/Should You Do

• Build Configurations (Instead of Plugins)
• Use Declarative Clients
  • HTTP
  • Kafka
  • RabbitMQ

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Configurations vs Plugins

• Consider Building Configurations instead of Plugins
• Work with Micronaut, Spring (with micronaut-spring) and Grails
• Plugins only work with Grails
• ... although some things only possible with Plugins (Views, taglibs etc.)

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[FIT] DEMO

Micronaut Configurations with Grails

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Micronaut Configurations

• Configuration with @ConfigurationProperties
• Beans with @Singleton, @Factory etc.
• Conditional Behaviour with @Requires
• Customization with @Replaces

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@ConfigurationProperties

Type Safe Configuration

@ConfigurationProperties("example")
class ExampleConfiguration {
	String name
}


ApplicationContext context = ApplicationContext.run("example.name":"Demo")
FooConfiguration config = context.getBean(FooConfiguration)
assert config.name == 'Demo'

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@Requires

Conditional Beans Made Easy

@Requires(property="example.enabled")
@Requires(beans=DataSource)
@Requires(missingBeans=Example)
@Singleton
class DefaultExampleBean implements Example {
	...
}

def context = ApplicationContext.run("example.enabled":"true")
Example example = context.getBean(Example)

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@Replaces

Easily Replace Beans by Type

@Replaces(DefaultExample)
@Singleton
class AlternativeExample implements Example {
	...
}

• Types match much
• Beans annotated with @Infrastructure not replaceable

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[FIT] DEMO

Micronaut HTTP Client

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@Client

Declarative Compile Time HTTP Clients

@Client("https://api.github.com")
@Header(name="User-Agent", value="micronaut-client")
interface GithubClient {
	@Get("/repos/{+slug}")
	Info getInfo(String slug)
}

• Blocking or Non-Blocking (RxJava, Reactor or Future)
• Reflection / Runtime Proxy Free

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@Client

• Uses Micronaut's low-level HTTP client (RxHttpClient) under the hood
• Built with Micronaut AOP (reflection/runtime proxy free)
• Works on GraalVM nativeimage
• Integrates with Tracing, Metrics, Service Discovery etc.

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[FIT] DEMO

Micronaut Kafka Client

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@KafkaClient

Declarative Compile Time Kafka Clients

@KafkaClient 
public interface ProductClient {
    @Topic("my-products") 
    void sendProduct(@KafkaKey String brand, String name); 
}

• Blocking or Non-Blocking (RxJava, Reactor or Future)

https://github.com/micronaut-projects/micronaut-kafka

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@RabbitClient

Declarative Compile Time Kafka Clients

@RabbitClient("animals") 
interface AnimalClient {
    void send(@Header String animalType, Animal animal) 
}

• Blocking or Non-Blocking (RxJava, Reactor or Future)

https://github.com/micronaut-projects/micronaut-rabbitmq

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Micronaut Message Consumers

• Micronaut Supports Message-Drive Microservices
• Can be run as standalone processes (No HTTP server)
• Use @RabbitListener for Rabbit
• Use @KafkaListener for Kafka

https://docs.micronaut.io/1.1.x/guide/index.html#messaging

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Micronaut's Clients

• Compile Time
• Reflection and Runtime Proxy Free
• Java, Groovy or Kotlin
• Built with Micronaut AOP

https://docs.micronaut.io/1.1.x/guide/index.html#aop

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Summary

• Micronaut Provides an Awesome Foundation
• Building Blocks to Create Libraries, Configurations and Clients
• Most Micronaut Features Available in Grails
• Build Micronaut Libraries not Plugins

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[FIT] Q & A

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