gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/jsr223/ScriptEngineCache.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.tinkerpop.gremlin.jsr223;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * A cache of standard {@code ScriptEngine} instances, instantiated by the standard {@code ScriptEngineManager}.
 * These instances are NOT "Gremlin-enabled". See {@link SingleGremlinScriptEngineManager} for the analogous class
 * that loads {@link GremlinScriptEngine} instances.
 *
 * @author Daniel Kuppitz (http://gremlin.guru)
 * @author Stephen Mallette (http://stephen.genoprime.com)
 */
public final class ScriptEngineCache {

    private ScriptEngineCache() {}

    public final static String DEFAULT_SCRIPT_ENGINE = "gremlin-groovy";

    private final static ScriptEngineManager SCRIPT_ENGINE_MANAGER = new ScriptEngineManager();
    private final static Map<String, ScriptEngine> CACHED_ENGINES = new ConcurrentHashMap<>();

    public static ScriptEngine get(final String engineName) {
        return CACHED_ENGINES.compute(engineName, (key, engine) -> {
            if (null == engine) {
                engine = SCRIPT_ENGINE_MANAGER.getEngineByName(engineName);
                if (null == engine) {
                    throw new IllegalArgumentException("There is no script engine with provided name: " + engineName);
                }
            }
            return engine;
        });
    }
}