Contents

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>
Note
 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 microprofile-config.properties file and Neo4j driver will be configured by Helidon and can be injected using CDI.

First describe Neo4j connection properties:

# Neo4j settings
neo4j.uri=bolt://localhost:7687
neo4j.authentication.username=neo4j
neo4j.authentication.password=secret
neo4j.pool.metricsEnabled=true

Then just inject the driver:

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

The driver can be used according to the Neo4j documentation.

Configuration

Type: io.helidon.integrations.neo4j.Neo4j

Configuration options

Table 1. Optional configuration options
key type default value description

authentication-enabled

boolean

true

Enable authentication.

certificate

Path

 

Set certificate path.

connection-acquisition-timeout

Duration

PT1M

Set connection acquisition timeout.

encrypted

boolean

 

Enable encrypted field.

hostname-verification-enabled

boolean

 

Enable hostname verification.

idle-time-before-connection-test

Duration

PT1MS

Set idle time.

log-leaked-sessions

boolean

 

Enable log leaked sessions.

max-connection-lifetime

Duration

PT5H

Set max life time.

max-connection-pool-size

int

100

Set pool size.

metrics-enabled

boolean

 

Enable metrics.

password

string

 

Create password.

trust-strategy

TrustStrategy (TRUST_ALL_CERTIFICATES, TRUST_CUSTOM_CA_SIGNED_CERTIFICATES, TRUST_SYSTEM_CA_SIGNED_CERTIFICATES)

 

Set trust strategy.

Allowed values:

  • TRUST_ALL_CERTIFICATES: Trust all.

  • TRUST_CUSTOM_CA_SIGNED_CERTIFICATES: Trust custom certificates.

  • TRUST_SYSTEM_CA_SIGNED_CERTIFICATES: Trust system CA.

uri

string

 

Create uri.

username

string

 

Create username.

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

# Enable the optional MicroProfile Metrics REST.request metrics
metrics.rest-request.enabled=true

This includes both connection information and enables Neo4j metrics propagation.

Finally, we are able to inject and use the Neo4j driver.

@ApplicationScoped
public class MovieRepository {

    private final Driver driver;

    @Inject
    public MovieRepository(Driver driver) { // (1)
        this.driver = driver;
    }

    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);
            }));
        }
    }
}

  1. Neo4j driver constructor injection

  2. Use of Neo4j driver to extract all Movies

Movies can now be returned as JSON objects:

@GET
@Produces(MediaType.APPLICATION_JSON)
public List<Movie> getAllMovies() {
    return movieRepository.findAll();
}

Now build and run.

mvn package
java -jar target/helidon-examples-integration-neo4j-mp.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 GitHub 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>
Note
 Works with Neo4j Integration main dependency described in Maven Coordinates.

To enable metrics in Neo4j, add the following property to microprofile-config.properties:

neo4j.pool.metricsEnabled=true

By applying these two actions, 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>
Note
 Works with Neo4j Integration main dependency described in Maven Coordinates.

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

References