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>

Copied

Check Neo4j Metrics Propagation and Neo4j Health Checks for additional dependencies for Neo4j Metrics and Health Checks integration.

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.

To implement Neo4j, you must first provide the connection properties as shown below:

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

Copied

Then just get the driver:

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

Copied

The driver can be used according to the Neo4j documentation.

Configuration

MicroProfile configuration options:

key	type	default value	description
`mp.jwt.verify.publickey`	string		The property allows the Public Verification Key text itself to be supplied as a string.
`authentication.username`	string		Neo4j authentication user name
`authentication.password`	string		Neo4j authentication password
`authentication.enabled`	boolean	TRUE	If Neo4j authentication is enabled
`encrypted`	boolean	FALSE	If Neo4j encryption is enabled
`pool.metricsEnabled`	boolean	FALSE	If Neo4J metrics is enabled
`pool.logLeakedSessions`	boolean		Log leaking sessions
`pool.maxConnectionPoolSize`	string		Maximum connection pool size
`pool.idleTimeBeforeConnectionTest`	string		Idle time before connection test
`pool.maxConnectionLifetime`	string		Connection lifetime in seconds
`pool.connectionAcquisitionTimeout`	string		Connection Acquisition Timeout
`trustsettings.trustStrategy`	string		Trust Strategy: Trust All certificates, `TRUST_ALL_CERTIFICATES`, Trust custom certificates - `TRUST_CUSTOM_CA_SIGNED_CERTIFICATES`, Trust system CA - `TRUST_SYSTEM_CA_SIGNED_CERTIFICATES`
`trustsettings.certificate`	string		Path to trusted certificate
`trustsettings.hostnameVerificationEnabled`	string	FALSE	If hostname verification is enabled.

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

Copied

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:

 <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>

Copied

Next add the connection configuration properties for Neo4j:

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

Copied

This includes both connection information and enables Neo4j metrics propagation.

Finally, we are able to use the Neo4j driver.

@ApplicationScoped
public class MovieRepository {

    private final Driver driver;

    public MovieRepository(Driver driver) { 
        this.driver = driver;
    }

    public List<Movie> findAll() { 

        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.readTransaction(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));
                });

                var m = new Movie(movieNode.get("title").asString(), movieNode.get("tagline").asString());
                m.setReleased(movieNode.get("released").asInt());
                m.setDirectorss(directors);
                m.setActors(actors);
                return m;
            }));
        }
    }
}

Copied

Constructor with Neo4j driver parameter
Use Neo4j driver to extract all Movies

Movies can now be returned as JSON objects:

public class MovieService implements Service {
    private final MovieRepository movieRepository;

    public MovieService(MovieRepository movieRepository) {
        this.movieRepository = movieRepository;
    }

    @Override
    public void update(Routing.Rules rules) {
        rules.get("/api/movies", this::findMoviesHandler);
    }

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

Copied

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

private static Routing createRouting(Config config) {

        MetricsSupport metrics = MetricsSupport.create();

        Neo4j neo4j = Neo4j.create(config.get("neo4j")); 

        // registers all metrics
        Neo4jMetricsSupport.builder() 
                .driver(neo4j.driver())
                .build()
                .initialize();

        Neo4jHealthCheck healthCheck = Neo4jHealthCheck.create(neo4j.driver()); 

        Driver neo4jDriver = neo4j.driver();

        MovieService movieService = new MovieService(new MovieRepository(neo4jDriver)); 

        HealthSupport health = HealthSupport.builder()
                .addLiveness(HealthChecks.healthChecks())   // Adds a convenient set of checks
                .addReadiness(healthCheck)
                .build();

        return Routing.builder() 
                .register(health)                   // Health at "/health"
                .register(metrics)                  // Metrics at "/metrics"
                .register(movieService)
                .build();
        }

Copied

Use of Neo4j support object to initialise and configure the driver.
Use of Neo4jMetricsSupport to add Neo4j metrics to /metrics output.
Use of Neo4jHealthCheck to add Neo4j health support.
Initialize MovieService with Neo4j driver.
Register the services in Routing.

Now build and run with JDK17+

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

Copied

Exercise the application:

curl -X GET http://localhost:8080/movies
{. . .}

# Try health and metrics
curl -s -X GET http://localhost:8080/health
{"outcome":"UP",...
. . .

# Prometheus Format
curl -s -X GET http://localhost:8080/metrics
# TYPE base:gc_g1_young_generation_count gauge
. . .

# JSON Format
curl -H 'Accept: application/json' -X GET http://localhost:8080/metrics
{"base":...
. . .

Copied

Full example code is available in Helidon GitHub Repository.

Additional Information

Neo4j Metrics Propagation

Neo4j 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>

Copied

Works with Neo4j Integration main dependency described in Maven Coordinates.

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

pool:
   metricsEnabled: true

Copied

Finally, to initialize metrics run:

Neo4jMetricsSupport.builder()
        .driver(neo4j.driver())
        .build()
        .initialize();

Copied

Neo4j 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>

Copied

Works with Neo4j Integration main dependency described in Maven Coordinates.

To enable health checks run the following code:

Neo4jHealthCheck healthCheck = Neo4jHealthCheck.create(neo4j.driver());

HealthSupport health = HealthSupport.builder()
        .addReadiness(healthCheck)
        .build();

Copied

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

Contents

Overview

Maven Coordinates

Usage

Configuration

Examples

Additional Information

Neo4j Metrics Propagation

Neo4j Health Checks

References