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Bitsy v3 is a small, fast, embeddable, durable in-memory graph database that is compatible with Tinkerpop3

There is a newer version: 3.6.2

package com.lambdazen.bitsy.gremlin;

import org.apache.tinkerpop.gremlin.process.traversal.Step;
import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
import org.apache.tinkerpop.gremlin.process.traversal.TraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.step.HasContainerHolder;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.HasStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.GraphStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.NoOpBarrierStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.util.HasContainer;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;

//Bitsy traversal strategy based Tinkerpop's Neo4j implementation	
public class BitsyTraversalStrategy extends AbstractTraversalStrategy implements TraversalStrategy.ProviderOptimizationStrategy {
	private static final long serialVersionUID = 6405194525894707932L;
	private static final BitsyTraversalStrategy INSTANCE = new BitsyTraversalStrategy();

	private BitsyTraversalStrategy() {
	}

	@Override
	public void apply(final Traversal.Admin traversal) {
		for (final GraphStep originalGraphStep : TraversalHelper.getStepsOfClass(GraphStep.class, traversal)) {
			final BitsyGraphStep bitsyGraphStep = new BitsyGraphStep<>(originalGraphStep);
			TraversalHelper.replaceStep(originalGraphStep, bitsyGraphStep, traversal);
			Step currentStep = bitsyGraphStep.getNextStep();
			while (currentStep instanceof HasStep || currentStep instanceof NoOpBarrierStep) {
				if (currentStep instanceof HasStep) {
					for (final HasContainer hasContainer : ((HasContainerHolder) currentStep).getHasContainers()) {
						if (!GraphStep.processHasContainerIds(bitsyGraphStep, hasContainer))
							bitsyGraphStep.addHasContainer(hasContainer);
					}
					TraversalHelper.copyLabels(currentStep, currentStep.getPreviousStep(), false);
					traversal.removeStep(currentStep);
				}
				currentStep = currentStep.getNextStep();
			}
		}
	}

	public static BitsyTraversalStrategy instance() {
		return INSTANCE;
	}

}