AWS Neptune Gremlin Composite Index

I'm using gremlin-java. And I want to create a unique index and a composite-index. But Graph object doesn't provide createIndex function. I will work on aws-neptune.

Is there a way to create composite-index and unique-index on aws-neptune?

My expected indexes are:

CREATE INDEX ON :`VertexLabel1`(`country`,`value`)
CREATE UNIQUE INDEX ON :`VertexLabel2`(`x_id`)

Graph configuration:

@Bean
public Cluster gremlinCluster()
{
    return Cluster.build()
            .addContactPoint(GREMLIN_ENDPOINT)
            .port(GREMLIN_PORT)
            .enableSsl(GREMLIN_SSL_ENABLED)
            .create();
} 
...
@Bean
public GraphTraversalSource gremlinGraph(Cluster gremlinCluster)
{
    return traversal().withRemote(DriverRemoteConnection.using(gremlinCluster, "g"));
}