Create Maven Project

The pom.xml file is a good starting point for Helidon microservices that use Coherence as a data store.

Few things are worth pointing out:

1. The parent POM is set to io.helidon.applications:helidon-mp and we add Helidon MicroProfile bundle and JSON Binding support as dependencies. This ensures that all necessary Helidon dependencies are imported correctly.
2. We add Coherence CDI Server as a dependency, which ensures that Coherence server is started within Helidon application via CDI extension.
3. We add Coherence MicroProfile Config as a dependency, which allows us to configure Coherence using Helidon MP Configuration and changes Coherence logging defaults to align Coherence log output with Helidon logging format.
4. We configure Jandex plugin to index any CDI beans we may have, in order to speed up application startup.
5. We configure Jib plugin within a docker profile, which allows us to create Docker image for our service within Maven build, without the need for a separate Dockerfile.

Implement Data Model

The Task class on the right represents data model for our to-do items that is used both within REST API (as a way to marshal JSON requests and responses) and as a storage data model class in Coherence. It is a very simple, serializable POJO.

Coherence provides more efficient serialization mechanisms as well, but in this example we are using plain Java serialization for simplicity.

Implement REST API

The REST API is implemented as a JAX-RS resource that will be automatically discovered and deployed by Helidon.

Coherence NamedMap instance is injected as a dependency by CDI, and is used to implement data access logic in the various resource methods.

Some of the resource methods, such as createTask and deleteTask are fairly simple and perform familiar Map.put and Map.remove operations against Coherence NamedMap.

The remaining two methods are a bit more interesting and demonstrate some of the additional features of NamedMap. The getTasks method shows usage of Coherence Query API, and calls NamedMap.values to retrieve filtered, sorted set of results.

The updateTask method on the other hand shows an example of entry processor execution against a single entry by sending a lambda to a storage member that owns the task with a given identifier, and updating the task in-place.

Enable CDI

Our service is a CDI Bean Archive, so we need to make sure it is treated that way by adding beans.xml file to the resources/META-INF directory.

Configure Logging

Both Coherence and Helidon are configured to use Java Logging, so we need to provide necessary Java Logging configuration by adding logging.properties file on the right to the resources directory.

Build the Service

With all the pieces in place, we are now ready to compile the service and create a Docker image for it.

                                
                                    mvn clean install
                                    mvn package -P docker
                                
                            

Run the Service

Once the Docker image is created, you can run the service locally.

                                
                                    docker run -m 200MB -p 7001:7001 coherence/quickstart
                                
                            

Test the Service

Now that the service is up and running, you can make HTTP request to the API endpoints using HTTP client of your choice. We strongly recommend Postman but curl will do.

                                
                                    curl -i -X POST -H "Content-Type: application/json" -d '{"description": "Learn Coherence"}' http://localhost:7001/tasks
                                    (out)HTTP/1.1 204 No Content
                                    (out)Date: Tue, 23 Jun 2020 10:40:57 GMT
                                    (out)connection: keep-alive
                                    (out)
                                    curl -X GET -H "Accept: application/json" http://localhost:7001/tasks
                                    (out)[{"completed":false,"description":"Learn Coherence","id":"155512ed-bf79-4515-a92a-734f65e721d0"}]
                                    (out)
                                    curl -X PUT -H "Content-Type: application/json" -d '{"completed": true}' http://localhost:7001/tasks/155512ed-bf79-4515-a92a-734f65e721d0
                                    (out){"completed":true,"description":"Learn Coherence","id":"155512ed-bf79-4515-a92a-734f65e721d0"}
                                    (out)
                                    curl -i -X DELETE http://localhost:7001/tasks/155512ed-bf79-4515-a92a-734f65e721d0
                                    (out)HTTP/1.1 204 No Content
                                    (out)Date: Tue, 23 Jun 2020 10:50:05 GMT
                                    (out)connection: keep-alive