Groovy-Powered Microservices with Micronaut

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© 2022, Object Computing, Inc. (OCI). All rights reserved. No part of these notes may be reproduced, stored in a retrieval system, or transmitted, in any
form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior, written permission of Object Computing, Inc. (OCI)
Groovy-Powered Microservices
with Micronaut
Zachary Klein, Principal Software Engineer, 2GM Team

© 2022, Object Computing, Inc. (OCI). All rights reserved. objectcomputing.com
❖ Zachary Klein - Developer & Architect
❖ Principal Software Engineer at Object
Computing, Inc
❖ 12+ years of software development experience
❖ OSS contributor
❖ Training instructor
2
About me

Copyright © 2022 Object Computing, Inc. (OCI) All rights reserved.
A modern, JVM-based, full-stack framework for building modular,
easily testable microservice and serverless applications.

https://micronaut.io/launch

❖ Controller with
Dependency Injection

❖ Micronaut is language-agnostic
❖ 1st Class support for:
❖ Java
❖ Kotlin
❖ Groovy
6
Micronaut and Groovy

❖ Micronaut implements core framework
components using Groovy language features
❖ E.g, Groovy AST transformations are used
for AOT compilation support (vs Annotation
Processors in Java/Kotlin)
❖ Support for Groovy configuration files,
serverless functions, Spock/Geb tests, and
GORM!
7
Micronaut and Groovy

❖ Controller with
Dependency Injection
❖ New class files generated
at compilation time (via
AST Transformations) to
implement the controller,
instantiate & supply
dependencies, etc

❖ Micronaut Launch is the recommended
method for creating Micronaut apps
❖ Choose Groovy as the Language (and
Spock as testing framework, if desired)
❖ Using the CLI:
10
Getting Started

© 2022, Object Computing, Inc. (OCI). All rights reserved. objectcomputing.com 11
Getting Started

Getting Started

Getting Started
Groovy auto-imports the
groovy.lang.singleton
annotation - make sure you
import from jakarta.inject
!

❖ Dependency Injection via
@Inject

❖ Micronaut’s HTTP Client
(implemented through
Groovy AST
Transformations)

❖ Dependency Injection via
Constructor Injection

❖ YAML is the default, but Groovy
is supported
❖ Groovy allows for powerful,
expressive, programmatic
configuration
❖ Can mix and match!
17
Configuration with Groovy

Configuration with Groovy
❖ Micronaut accepts
configuration in JSON,
properties, YAML, and
Groovy ConfigSlurper (also
env variables, system
properties)
❖ Note that properties cannot
contain dashes - use
camelCase or snake_case

❖ Micronaut Controllers (and Clients) express routes
declaratively via annotation arguments:
❖ @Controller("/hello")
❖ @Get("/profile “)
❖ Optionally, routes can be expressed
programmatically using the RouteBuilder interface
❖ GroovyRouteBuilder provides an expressive DSL
for routes (similar to Grails UrlMappings)
19
Controller Routes

Controller Routes
❖ Annotation-based routes

Controller Routes
❖ GroovyRouteBuilder

@MicronautTest & Spock
❖ Micronaut is test-framework agnostic - no special
tooling required
❖ E.g, JUnit, Spock
❖ Because of Micronaut’s fast startup time, many
developers prefer integration tests
❖ @MicronautTest automatically starts up the
application context for the test run, and shuts it
down cleanly

Micronaut and GORM
❖ GORM is the persistence framework pioneered by
the Grails framework - https://gorm.grails.org
❖ GORM provides expressive querying, persistence
and domain modeling features, including
validation, multi-tenancy, and more
❖ When configured with Groovy support, Micronaut
apps can leverage GORM’s powerful features in a
comparatively lightweight manner

Micronaut and GORM
Dependency Description
micronaut-
hibernate-gorm
Configures GORM for Hibernate for Groovy
applications
micronaut-mongo-
gorm
Configures GORM for Mongo DB for Groovy
applications
micronaut-neo4j-
gorm
Configures GORM for Mongo DB for Groovy
applications

Adding GORM to Micronaut
❖ Using Micronaut Launch
or the CLI command
feature-diff, you can
generate a delta showing
how to add a feature, like
hibernate-gorm

Adding GORM to Micronaut
❖ Add GORM and JDBC
dependencies - also a
database driver (H2 in this
demo)

Configuring Datasources
❖ Datasource configuration
❖ Standard Hibernate/JDBC
configuration properties -
database credentials,
dialect, etc
❖ Can configure multiple
datasources

Enabling Entity-scanning
❖ Application class needs to
be modified
❖ Application context is
started up using the
builder pattern - the
packages() method
species the package under
which entities are defined

Creating Domain Classes (aka Entities)
❖ A Domain Class / Entity can
be a simple POGO
annotated with @Entity
❖ Class name will be mapped
as database table name (by
convention)
❖ Properties of the class will be
mapped to columns in the
database table

Creating Domain Classes (aka Entities)
❖ Additional data-mapping
features (like validation)
can be added by
implementing the
GormEntity<> trait

GORM Data Services in Micronaut

GORM Multi-tenancy
https://gorm.grails.org/latest/hibernate/manual/index.html#multiTenancy

GORM Multi-tenancy

GORM Multi-tenancy Modes
Modes Description Isolation
DATABASE
Separate database with a
separate connection pool is used
to store each tenants data.
HIGHEST
SCHEMA
The same database, but different
schemas are used to store each
tenants’ data.
HIGH
DISCRIMINATOR
The same database is used with
a discriminator used to partition
and isolate data.
LOW

GORM Multi-tenancy Tenant Resolvers
Name Description
CookieTenantResolver Removes the current tenant from an HTTP cookie
FixedTenantResolver Resolves against a fixed tenant id
HttpHeaderTenantResolver Resolves the current tenant from the request HTTP Header
PrincipalTenantResolver Resolves the current tenant from the authenticated username
SessionTenantResolver Resolves the current tenant from the HTTP Session
SubdomainTenantResolver Resolves the tenant id from the subdomain
SystemPropertyTenantResolver Resolves the tenant id from a system property

GORM Multi-tenancy: Specify tenantId

GORM Multi-tenancy Transformations (Annotations)
Transformation Description
@CurrentTenant Resolve the current tenant for the context of a class or method
@Tenant Use a specifc tenant for the context of a class or method
@WithoutTenant Execute logic without a specific tentnat (using the default connection)

Micronaut and Grails
❖ Grails is a rapid-application Java web-framework, based on
Groovy and Spring Boot
❖ Since Grails 4, Grails applications include a Micronaut
application context, allowing Micronaut features and libraries
to be integrated with Grails apps
❖ Micronaut HTTP Client & Grails: https://guides.grails.org/
grails-micronaut-http/guide/index.html
❖ Micronaut Kafka & Grails: https://guides.grails.org/grails-
micronaut-kafka/guide/index.html

❖ Micronaut supports Groovy for writing serverless
functions in environments like AWS Lambda, Oracle
Cloud, Microsoft Azure, & Google Cloud Platform.
❖ You can deploy “pure” functions (invoked by events in
the platform) or lightweight “HTTP functions” (with
controllers, REST endpoints, etc)
48
Micronaut and Groovy: Serverless Functions

https://micronaut-projects.github.io/
micronaut-gcp/latest/guide/

micronaut-aws/latest/guide/

micronaut-azure/latest/guide/

micronaut-oracle-cloud/latest/guide/

Micronaut and Groovy: CLI Apps
❖ Micronaut supports creation of Command Line
Applications using the picocli library (https://picocli.info/)
❖ CLI apps can be created using Groovy as well!
❖ Apps can utilize dependency injection, HTTP clients, &
more
❖ Docs: https://micronaut-projects.github.io/micronaut-
picocli/latest/guide/

Micronaut and Groovy: CLI Apps

objectcomputing.com
© 2022, Object Computing, Inc. (OCI). All rights reserved. No part of these notes may be reproduced, stored in a retrieval system, or transmitted, in any
form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior, written permission of Object Computing, Inc. (OCI)
Zachary Klein, Principal Software Engineer, 2GM Team

Groovy-Powered Microservices with Micronaut

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