Java Micronaut REST Server with CockroachDB

🕓 45 minutes

What you’ll learn

How to set up your application for :

• connecting to CockroachDB database,
• getting data from REST API,
• providing data to REST API.

In this tutorial, we will create a simple java component with Java Micronaut scaffolder with a connection to CockroachDB database storage. We want to expose a single REST endpoint for getting the basic client data information, creating a microservice CRUD layer above the DB storage.

Project source

This example project can be cloned from: http://gitlab.cloud.codenow.com/public-docs/java-micronaut-demo/rest-server-with-cockroachdb.git

Prerequisites

• Prepare your local development environment for CodeNOW with Micronaut.
  • Follow the tutorial instructions in the Java Micronaut Local Development tutorial.
• Run CockroachDB locally.
  • You can run CockroachDB directly or using docker compose.
  • The configuration file for docker-compose can be downloaded from this link: https://kb.objectrocket.com/cockroachdb/docker-compose-and-cockroachdb-1151
• Create a new component
  • For details see the section Prerequisites of the Java Micronaut Local Development tutorial.

Steps

Open your IDE, import the created component and start coding:

• First, add maven dependency to your pom.xml

  <dependency>

  <groupId>org.postgresql</groupId>

  <artifactId>postgresql</artifactId>

  <version>42.2.16</version>

  </dependency>

  <dependency>

  <groupId>javax.persistence</groupId>

  <artifactId>javax.persistence-api</artifactId>

  <version>2.2</version>

  </dependency>

  <dependency>

  <groupId>io.micronaut.data</groupId>

  <artifactId>micronaut-data-jdbc</artifactId>

  <version>1.1.3</version>

  </dependency>

  <dependency>

  <groupId>io.micronaut.configuration</groupId>

  <artifactId>micronaut-jdbc-hikari</artifactId>

  <scope>runtime</scope>

  </dependency>

  <dependency>

  <groupId>javax.annotation</groupId>

  <artifactId>javax.annotation-api</artifactId>

  <version>1.3.2</version>

  </dependency>

• Then define the jpa entity Client. This simple table will store basic client data:

  • Generate getters and setters with your IDE
  package io.codenow.client.data.db.service.repository.entity;

  import java.time.LocalDate;

  import javax.persistence.Entity;

  import javax.persistence.GeneratedValue;

  import javax.persistence.Id;

  @Entity

  public class Client {

  @Id

  @GeneratedValue

  private Long id;

  private String username;

  private String firstname;

  private String surname;

  private LocalDate birthdate;

  }

• Create a new ClientRepository, which is a basic CRUD interface for micronaut data DB access:

  package io.codenow.client.data.db.service.repository;

  import io.codenow.client.data.db.service.repository.entity.Client;

  import io.micronaut.data.jdbc.annotation.JdbcRepository;

  import io.micronaut.data.repository.CrudRepository;

  import io.reactivex.Maybe;

  @JdbcRepository

  public interface ClientRepository extends CrudRepository<Client, Long> {

  Maybe<Client> findByUsername(String username);

  }

• Create a new controller and put all the parts together

  • For more details about Micronaut controller, see: https://docs.micronaut.io/latest/guide/index.html#httpServer
  package io.codenow.client.data.db.service.controller;

  import javax.inject.Inject;

  import javax.validation.constraints.NotNull;

  import org.example.service.repository.ClientRepository;

  import org.example.service.model.Client;

  import io.micronaut.http.annotation.Consumes;

  import io.micronaut.http.annotation.Controller;

  import io.micronaut.http.annotation.Get;

  import io.micronaut.http.annotation.PathVariable;

  import io.micronaut.http.annotation.Produces;

  import io.micronaut.validation.Validated;

  import io.reactivex.Flowable;

  import io.reactivex.Maybe;

  /**

  * ClientDataController.

  */

  @Validated

  @Controller("/clients")

  @Produces

  @Consumes

  public class ClientDataController {

  private final ClientRepository clientRepository;

  @Inject

  public ClientDataController(ClientRepository clientRepository) {

  this.clientRepository = clientRepository;

  }

  @Get("/")

  public Flowable<Client> listClients() {

  return Flowable.fromIterable(clientRepository.findAll());

  }

  @Get("/{username}")

  public Maybe<Client> getClient(@PathVariable @NotNull String username) {

  return clientRepository.findByUsername(username);

  }

  }

• Next prepare the database configuration:

  • If you are using docker-compose or regular docker, then go to the cockroach sql terminal and create a new database.
    • You can use this link for help: https://kb.objectrocket.com/cockroachdb/docker-compose-and-cockroachdb-1151
  • Then create a new table with the name "client" inside your new database and fill it with values.

• Now change the configuration in codenow/config/application.yaml:

• Fill {db user} and {db password} according to your configuration

• Make sure you follow yaml syntax (especially whitespaces)

  datasources:

  default:

  url: jdbc:postgresql://localhost:5432/{db_name}

  driverClassName: org.postgresql.Driver

  username: {db user}

  password: {db password}

  dialect: POSTGRES

• Do not forget to change the swagger.yaml. Add these lines into your src/main/resources/META-INF/swagger/swagger.yaml :

  paths:

  /clients:

  get:

  tags:

  - data

  summary: Get all clients

  description: Return all clients from the database

  operationId: listClients

  responses:

  '200':

  description: response

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/Clients'

  '400':

  description: Bad request (e.g. validation)

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/ErrorMessage'

  '500':

  description: Server error

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/ErrorMessage'

  /clients/{username}:

  get:

  tags:

  - data

  summary: Client by username

  description: Return client by username

  operationId: getClient

  parameters:

  - name: username

  schema:

  type: string

  in: path

  description: username

  responses:

  '200':

  description: response

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/Client'

  '400':

  description: Bad request (e.g. validation)

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/ErrorMessage'

  '500':

  description: Server error

  content:

  application/json:

  schema:

  $ref: '#/components/schemas/ErrorMessage'

  components:

  schemas:

  ErrorMessage:

  type: object

  properties:

  errorId:

  type: string

  traceId:

  type: string

  errorDetail:

  type: string

  errorParams:

  type: array

  items:

  $ref: '#/components/schemas/ErrorParam'

  requestMapping:

  type: array

  items:

  type: string

  ErrorParam:

  type: object

  required:

  - key

  - value

  properties:

  key:

  type: string

  value:

  type: string

  Clients:

  type: array

  items:

  $ref: '#/components/schemas/Client'

  Client:

  required:

  - id

  - username

  - firstname

  - surname

  - birthdate

  type: object

• Try to build and run the application in your IDE. After startup, you should be able to access your new controller’s swagger: http://localhost:8080/swagger/index.html

  • For correct setup, check the Readme.md in the project root or see the tutorial Java Micronaut Local Development

Deploy to CodeNOW

If your code works in the local development, you are ready to push your changes to GIT and try to build and deploy your new component version to the CodeNOW environment.

• Check the Get New CockroachDB user manual to get CodeNOW managed component properties.
• Make sure to change the application.yaml properties from the local to the production setup.
• For more information about application deployment see Application Deployment and Deployment Monitoring tutorials.

What’s next?

See the tutorial Micronaut REST server with Redis and Kafka.