Neo4j

Overview

Neo4j is a graph database management system developed by Neo4j, Inc. It is an ACID-compliant transactional database with native graph storage and processing. Neo4j is available in a GPL3-licensed open-source “community edition”.

Maven Coordinates

To enable Neo4j, add the following dependency to your project’s pom.xml (see Managing Dependencies).

<dependency>
  <groupId>io.helidon.integrations.neo4j</groupId>
  <artifactId>helidon-integrations-neo4j</artifactId>
</dependency>

Usage

The support for Neo4j is implemented in Neo4j driver level. Just add the dependency, add configuration in application.yaml file and Neo4j driver will be configured by Helidon and can be used with Neo4j support object.

First describe Neo4j connection properties:

neo4j:
 uri: bolt://localhost:7687
 authentication:
   username: neo4j
   password: secret
 pool:
   metricsEnabled: true

Then just get the driver:

Neo4j neo4j = Neo4j.create(config.get("neo4j"));
Driver neo4jDriver = neo4j.driver();

The driver can be used according to the Neo4j documentation.

Configuration

Configuration options

Examples

This example implements a simple Neo4j REST service using MicroProfile. For this example a working Neo4j database is required. The Neo4j Movie database is used for this example.

Bring up a Neo4j instance via Docker

docker run --publish=7474:7474 --publish=7687:7687 -e 'NEO4J_AUTH=neo4j/secret'  neo4j:latest

Go to the Neo4j browser and play the first step of the movies graph: :play movies

Now go to the pom.xml and add the following dependencies:

<dependencies>
  <dependency>
    <groupId>io.helidon.integrations.neo4j</groupId>
    <artifactId>helidon-integrations-neo4j</artifactId>
  </dependency>
  <dependency>
    <groupId>io.helidon.integrations.neo4j</groupId>
    <artifactId>helidon-integrations-neo4j-metrics</artifactId>
  </dependency>
  <dependency>
    <groupId>io.helidon.integrations.neo4j</groupId>
    <artifactId>helidon-integrations-neo4j-health</artifactId>
  </dependency>
</dependencies>

Next add the connection configuration properties for Neo4j:

neo4j:
 uri: bolt://localhost:7687
 authentication:
   username: neo4j
   password: secret
 pool:
   metricsEnabled: true

This includes both connection information and enables Neo4j metrics propagation.

Finally, we are able to use the Neo4j driver.

record MovieRepository(Driver driver) {1

    List<Movie> findAll() {2
        try (var session = driver.session()) {
            var query = """
                        match (m:Movie)
                        match (m) <- [:DIRECTED] - (d:Person)
                        match (m) <- [r:ACTED_IN] - (a:Person)
                        return m, collect(d) as directors, collect({name:a.name, roles: r.roles}) as actors
                        """;

            return session.executeRead(tx -> tx.run(query).list(r -> {
                var movieNode = r.get("m").asNode();

                var directors = r.get("directors").asList(v -> {
                    var personNode = v.asNode();
                    return new Person(personNode.get("born").asInt(), personNode.get("name").asString());
                });

                var actors = r.get("actors").asList(v -> {
                    return new Actor(v.get("name").asString(), v.get("roles").asList(Value::asString));
                });

                return new Movie(
                        movieNode.get("title").asString(),
                        movieNode.get("tagline").asString(),
                        movieNode.get("released").asInt(),
                        directors,
                        actors);
            }));
        }
    }
}

Movies can now be returned as JSON objects:

record MovieService(MovieRepository movieRepository) implements HttpService {

    @Override
    public void routing(HttpRules rules) {
        rules.get("/api/movies", this::findMovies);
    }

    void findMovies(ServerRequest request, ServerResponse response) {
        response.send(this.movieRepository.findAll());
    }
}

To use the service, as well as to add metrics and health support the following routing should be created:

Neo4j neo4j = Neo4j.create(config.get("neo4j"));
Driver driver = neo4j.driver();1

Neo4jMetricsSupport.builder()
        .driver(driver)
        .build()
        .initialize();2

ObserveFeature observeFeature = ObserveFeature.builder()
        .addObserver(HealthObserver.builder()
                             .addCheck(Neo4jHealthCheck.create(driver))
                             .build())
        .build();3

WebServer server = WebServer.builder()
        .addFeature(observeFeature)
        .routing(it -> it.register(new MovieService(new MovieRepository(driver))))4
        .build()
        .start();

System.out.println("WEB server is up! http://localhost:" + server.port() + "/api/movies");

Now build and run.

mvn package
java -jar target/helidon-examples-integration-neo4j.jar

Exercise the application:

curl -X GET http://localhost:8080/movies

# Try health
curl -s -X GET http://localhost:8080/health

# Try metrics in Prometheus Format
curl -s -X GET http://localhost:8080/metrics

# Try metrics in JSON Format
curl -H 'Accept: application/json' -X GET http://localhost:8080/metrics

Full example code is available in Helidon Examples Repository.

Additional Information

Neo4j Metrics propagation

Neo4j’s metrics can be propagated to the user as MicroProfile metrics. This is implemented in a separate Maven module. Just add:

<dependency>
  <groupId>io.helidon.integrations.neo4j</groupId>
  <artifactId>helidon-integrations-neo4j-metrics</artifactId>
</dependency>

To enable metrics in Neo4j, add the following property to application.yaml:

pool:
   metricsEnabled: true

Finally, to initialize metrics run:

Neo4jMetricsSupport.builder()
        .driver(driver)
        .build()
        .initialize();

Neo4j’s metrics will be automatically added to the output of the /metrics endpoint.

Neo4j Health Checks

If your application is highly dependent on Neo4j database, health and liveness checks are essential for this application to work correctly.

MicroProfile Health checks for Neo4j are implemented in a separate Maven module:

<dependency>
  <groupId>io.helidon.integrations.neo4j</groupId>
  <artifactId>helidon-integrations-neo4j-health</artifactId>
</dependency>

To enable health checks run the following code:

ObserveFeature observeFeature = ObserveFeature.builder()
        .addObserver(HealthObserver.builder()
                             .addCheck(Neo4jHealthCheck.create(driver))
                             .build())
        .build();

Health checks for Neo4j will be included in /health endpoint output.

Reference

• Neo4j official website
• Neo4j Java developer guide