com.davidbracewell.scripting.ScriptEnvironmentManager Maven / Gradle / Ivy

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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.scripting;

import com.google.common.base.Preconditions;
import com.google.common.base.Strings;
import com.google.common.collect.Maps;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;
import java.util.List;
import java.util.Map;

/**
 * Manages scripting environments giving each language a singleton instance.
 *
 * @author David B. Bracewell
 */
public final class ScriptEnvironmentManager {

  private final Map environments;
  private final ScriptEngineManager engineManager;

  private static ScriptEnvironmentManager INSTANCE;

  /**
   * @return The instance of ScriptEnvironmentManager
   */
  public static synchronized ScriptEnvironmentManager getInstance() {
    if (INSTANCE == null) {
      INSTANCE = new ScriptEnvironmentManager();
    }
    return INSTANCE;
  }

  private ScriptEnvironmentManager() {
    environments = Maps.newConcurrentMap();
    engineManager = new ScriptEngineManager();
  }

  /**
   * Gets the scripting environment given the environment name.
   *
   * @param environmentName the scripting environment name
   * @return the scripting environment
   */
  public ScriptEnvironment getEnvironment(String environmentName) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(environmentName), "Environment name cannot be null or empty");
    ScriptEngine engine = engineManager.getEngineByName(environmentName);
    environmentName = engine.getFactory().getEngineName();
    if (!environments.containsKey(environmentName)) {
      environments.put(environmentName, new ScriptEnvironment(engine));
    }
    return environments.get(environmentName);
  }

  /**
   * Gets a temporary scripting environment given the environment name.
   *
   * @param environmentName the scripting environment name
   * @return the scripting environment
   */
  public static ScriptEnvironment getTemporaryEnvironment(String environmentName) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(environmentName), "Environment name cannot be null or empty");
    ScriptEngine engine = ScriptEnvironmentManager.getInstance().engineManager.getEngineByName(environmentName);
    return new ScriptEnvironment(engine);
  }


  /**
   * Gets the scripting environment given the script extension.
   *
   * @param extension the scripting environment extension
   * @return the scripting environment
   */
  public ScriptEnvironment getEnvironmentForExtension(String extension) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(extension), "Extension name cannot be null or empty");
    return getEnvironment(getEnvironmentNameForExtension(extension));
  }

  /**
   * Gets the scripting environment given the script extension.
   *
   * @param extension the scripting environment extension
   * @return the scripting environment
   */
  public static ScriptEnvironment getTemporaryEnvironmentForExtension(String extension) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(extension), "Extension name cannot be null or empty");
    return getTemporaryEnvironment(ScriptEnvironmentManager.getInstance().getEnvironmentNameForExtension(extension));
  }


  /**
   * Gets the scripting environment name given the script extension.
   *
   * @param extension the scripting environment extension
   * @return the scripting environment name
   */
  public String getEnvironmentNameForExtension(String extension) {
    Preconditions.checkArgument(!Strings.isNullOrEmpty(extension), "Extension name cannot be null or empty");
    ScriptEngine engine = engineManager.getEngineByExtension(extension);
    if (engine == null) {
      throw new IllegalStateException(extension + " is not a recognized scripting extension.");
    }
    return engine.getFactory().getLanguageName();
  }

  /**
   *  Returns an array whose elements are instances of all the ScriptEngineFactory classes found by the discovery
   * mechanism. 
   *
   * @return an array whose elements are instances of all the ScriptEngineFactory classes found by the discovery
   *         mechanism.
   * @see javax.script.ScriptEngineManager#getEngineFactories()
   */
  public List getAvailableEngines() {
    ScriptEngineManager engineManager = new ScriptEngineManager();
    return engineManager.getEngineFactories();
  }

}//END OF ScriptEnvironmentManager