Ejemplo en Java de conexión a una instancia de base de datos de Neptune con lógica de reconexión

El siguiente ejemplo de Java muestra cómo conectarse al cliente de Gremlin con una lógica de reconexión para recuperarse de una desconexión inesperada.

Tiene las siguientes dependencias:

<dependency>
    <groupId>org.apache.tinkerpop</groupId>
    <artifactId>gremlin-driver</artifactId>
    <version>${gremlin.version}</version>
</dependency>

<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>amazon-neptune-sigv4-signer</artifactId>
    <version>${sig4.signer.version}</version>
</dependency>

<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>amazon-neptune-gremlin-java-sigv4</artifactId>
    <version>${sig4.signer.version}</version>
</dependency>

<dependency>
    <groupId>com.evanlennick</groupId>
    <artifactId>retry4j</artifactId>
    <version>0.15.0</version>
</dependency>

Este es el código de ejemplo:

public static void main(String args[]) {
  boolean useIam = true;

  // Create Gremlin cluster and traversal source
  Cluster.Builder builder = Cluster.build()
         .addContactPoint(System.getenv("neptuneEndpoint"))
         .port(Integer.parseInt(System.getenv("neptunePort")))
         .enableSsl(true)
         .minConnectionPoolSize(1)
         .maxConnectionPoolSize(1)
         .serializer(Serializers.GRAPHBINARY_V1D0)
         .reconnectInterval(2000);

  if (useIam) {
    builder = builder.channelizer(SigV4WebSocketChannelizer.class);
  }

  Cluster cluster = builder.create();

  GraphTraversalSource g = AnonymousTraversalSource
      .traversal()
      .withRemote(DriverRemoteConnection.using(cluster));

  // Configure retries
  RetryConfig retryConfig = new RetryConfigBuilder()
      .retryOnCustomExceptionLogic(getRetryLogic())
      .withDelayBetweenTries(1000, ChronoUnit.MILLIS)
      .withMaxNumberOfTries(5)
      .withFixedBackoff()
      .build();

  @SuppressWarnings("unchecked")
  CallExecutor<Object> retryExecutor = new CallExecutorBuilder<Object>()
      .config(retryConfig)
      .build();

  // Do lots of queries
  for (int i = 0; i < 100; i++){
    String id = String.valueOf(i);

    @SuppressWarnings("unchecked")
    Callable<Object> query = () -> g.V(id)
        .fold()
        .coalesce(
            unfold(),
            addV("Person").property(T.id, id))
        .id().next();

    // Retry query
    // If there are connection failures, the Java Gremlin client will automatically
    // attempt to reconnect in the background, so all we have to do is wait and retry.
    Status<Object> status = retryExecutor.execute(query);

    System.out.println(status.getResult().toString());
  }

  cluster.close();
}

private static Function<Exception, Boolean> getRetryLogic() {

  return e -> {

    Class<? extends Exception> exceptionClass = e.getClass();

    StringWriter stringWriter = new StringWriter();
    String message = stringWriter.toString();


    if (RemoteConnectionException.class.isAssignableFrom(exceptionClass)){
      System.out.println("Retrying because RemoteConnectionException");
      return true;
    }

    // Check for connection issues
    if (message.contains("Timed out while waiting for an available host") ||
        message.contains("Timed-out waiting for connection on Host") ||
        message.contains("Connection to server is no longer active") ||
        message.contains("Connection reset by peer") ||
        message.contains("SSLEngine closed already") ||
        message.contains("Pool is shutdown") ||
        message.contains("ExtendedClosedChannelException") ||
        message.contains("Broken pipe") ||
        message.contains(System.getenv("neptuneEndpoint")))
    {
      System.out.println("Retrying because connection issue");
      return true;
    };

    // Concurrent writes can sometimes trigger a ConcurrentModificationException.
    // In these circumstances you may want to backoff and retry.
    if (message.contains("ConcurrentModificationException")) {
      System.out.println("Retrying because ConcurrentModificationException");
      return true;
    }

    // If the primary fails over to a new instance, existing connections to the old primary will
    // throw a ReadOnlyViolationException. You may want to back and retry.
    if (message.contains("ReadOnlyViolationException")) {
      System.out.println("Retrying because ReadOnlyViolationException");
      return true;
    }

    System.out.println("Not a retriable error");
    return false;
  };
}