Java tutorial
/* * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.script; import java.util.*; import java.security.*; import java.util.ServiceLoader; import java.util.ServiceConfigurationError; /** * The <code>ScriptEngineManager</code> implements a discovery and instantiation * mechanism for <code>ScriptEngine</code> classes and also maintains a * collection of key/value pairs storing state shared by all engines created * by the Manager. This class uses the service provider mechanism described in the * {@link java.util.ServiceLoader} class to enumerate all the * implementations of <code>ScriptEngineFactory</code>. <br><br> * The <code>ScriptEngineManager</code> provides a method to return a list of all these factories * as well as utility methods which look up factories on the basis of language name, file extension * and mime type. * <p> * The <code>Bindings</code> of key/value pairs, referred to as the "Global Scope" maintained * by the manager is available to all instances of <code>ScriptEngine</code> created * by the <code>ScriptEngineManager</code>. The values in the <code>Bindings</code> are * generally exposed in all scripts. * * @author Mike Grogan * @author A. Sundararajan * @since 1.6 */ public class ScriptEngineManager { private static final boolean DEBUG = false; /** * The effect of calling this constructor is the same as calling * <code>ScriptEngineManager(Thread.currentThread().getContextClassLoader())</code>. * * @see java.lang.Thread#getContextClassLoader */ public ScriptEngineManager() { ClassLoader ctxtLoader = Thread.currentThread().getContextClassLoader(); init(ctxtLoader); } /** * This constructor loads the implementations of * <code>ScriptEngineFactory</code> visible to the given * <code>ClassLoader</code> using the service provider mechanism.<br><br> * If loader is <code>null</code>, the script engine factories that are * bundled with the platform are loaded. <br> * * @param loader ClassLoader used to discover script engine factories. */ public ScriptEngineManager(ClassLoader loader) { init(loader); } private void init(final ClassLoader loader) { globalScope = new SimpleBindings(); engineSpis = new TreeSet<ScriptEngineFactory>(Comparator.comparing(ScriptEngineFactory::getEngineName, Comparator.nullsLast(Comparator.naturalOrder()))); nameAssociations = new HashMap<String, ScriptEngineFactory>(); extensionAssociations = new HashMap<String, ScriptEngineFactory>(); mimeTypeAssociations = new HashMap<String, ScriptEngineFactory>(); initEngines(loader); } private ServiceLoader<ScriptEngineFactory> getServiceLoader(final ClassLoader loader) { if (loader != null) { return ServiceLoader.load(ScriptEngineFactory.class, loader); } else { return ServiceLoader.loadInstalled(ScriptEngineFactory.class); } } private void initEngines(final ClassLoader loader) { Iterator<ScriptEngineFactory> itr = null; try { ServiceLoader<ScriptEngineFactory> sl = AccessController .doPrivileged(new PrivilegedAction<ServiceLoader<ScriptEngineFactory>>() { @Override public ServiceLoader<ScriptEngineFactory> run() { return getServiceLoader(loader); } }); itr = sl.iterator(); } catch (ServiceConfigurationError err) { System.err.println("Can't find ScriptEngineFactory providers: " + err.getMessage()); if (DEBUG) { err.printStackTrace(); } // do not throw any exception here. user may want to // manage his/her own factories using this manager // by explicit registratation (by registerXXX) methods. return; } try { while (itr.hasNext()) { try { ScriptEngineFactory fact = itr.next(); engineSpis.add(fact); } catch (ServiceConfigurationError err) { System.err.println("ScriptEngineManager providers.next(): " + err.getMessage()); if (DEBUG) { err.printStackTrace(); } // one factory failed, but check other factories... continue; } } } catch (ServiceConfigurationError err) { System.err.println("ScriptEngineManager providers.hasNext(): " + err.getMessage()); if (DEBUG) { err.printStackTrace(); } // do not throw any exception here. user may want to // manage his/her own factories using this manager // by explicit registratation (by registerXXX) methods. return; } } /** * <code>setBindings</code> stores the specified <code>Bindings</code> * in the <code>globalScope</code> field. ScriptEngineManager sets this * <code>Bindings</code> as global bindings for <code>ScriptEngine</code> * objects created by it. * * @param bindings The specified <code>Bindings</code> * @throws IllegalArgumentException if bindings is null. */ public void setBindings(Bindings bindings) { if (bindings == null) { throw new IllegalArgumentException("Global scope cannot be null."); } globalScope = bindings; } /** * <code>getBindings</code> returns the value of the <code>globalScope</code> field. * ScriptEngineManager sets this <code>Bindings</code> as global bindings for * <code>ScriptEngine</code> objects created by it. * * @return The globalScope field. */ public Bindings getBindings() { return globalScope; } /** * Sets the specified key/value pair in the Global Scope. * @param key Key to set * @param value Value to set. * @throws NullPointerException if key is null. * @throws IllegalArgumentException if key is empty string. */ public void put(String key, Object value) { globalScope.put(key, value); } /** * Gets the value for the specified key in the Global Scope * @param key The key whose value is to be returned. * @return The value for the specified key. */ public Object get(String key) { return globalScope.get(key); } /** * Looks up and creates a <code>ScriptEngine</code> for a given name. * The algorithm first searches for a <code>ScriptEngineFactory</code> that has been * registered as a handler for the specified name using the <code>registerEngineName</code> * method. * <br><br> If one is not found, it searches the set of <code>ScriptEngineFactory</code> instances * stored by the constructor for one with the specified name. If a <code>ScriptEngineFactory</code> * is found by either method, it is used to create instance of <code>ScriptEngine</code>. * @param shortName The short name of the <code>ScriptEngine</code> implementation. * returned by the <code>getNames</code> method of its <code>ScriptEngineFactory</code>. * @return A <code>ScriptEngine</code> created by the factory located in the search. Returns null * if no such factory was found. The <code>ScriptEngineManager</code> sets its own <code>globalScope</code> * <code>Bindings</code> as the <code>GLOBAL_SCOPE</code> <code>Bindings</code> of the newly * created <code>ScriptEngine</code>. * @throws NullPointerException if shortName is null. */ public ScriptEngine getEngineByName(String shortName) { if (shortName == null) throw new NullPointerException(); //look for registered name first Object obj; if (null != (obj = nameAssociations.get(shortName))) { ScriptEngineFactory spi = (ScriptEngineFactory) obj; try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } for (ScriptEngineFactory spi : engineSpis) { List<String> names = null; try { names = spi.getNames(); } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } if (names != null) { for (String name : names) { if (shortName.equals(name)) { try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } } } } return null; } /** * Look up and create a <code>ScriptEngine</code> for a given extension. The algorithm * used by <code>getEngineByName</code> is used except that the search starts * by looking for a <code>ScriptEngineFactory</code> registered to handle the * given extension using <code>registerEngineExtension</code>. * @param extension The given extension * @return The engine to handle scripts with this extension. Returns <code>null</code> * if not found. * @throws NullPointerException if extension is null. */ public ScriptEngine getEngineByExtension(String extension) { if (extension == null) throw new NullPointerException(); //look for registered extension first Object obj; if (null != (obj = extensionAssociations.get(extension))) { ScriptEngineFactory spi = (ScriptEngineFactory) obj; try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } for (ScriptEngineFactory spi : engineSpis) { List<String> exts = null; try { exts = spi.getExtensions(); } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } if (exts == null) continue; for (String ext : exts) { if (extension.equals(ext)) { try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } } } return null; } /** * Look up and create a <code>ScriptEngine</code> for a given mime type. The algorithm * used by <code>getEngineByName</code> is used except that the search starts * by looking for a <code>ScriptEngineFactory</code> registered to handle the * given mime type using <code>registerEngineMimeType</code>. * @param mimeType The given mime type * @return The engine to handle scripts with this mime type. Returns <code>null</code> * if not found. * @throws NullPointerException if mimeType is null. */ public ScriptEngine getEngineByMimeType(String mimeType) { if (mimeType == null) throw new NullPointerException(); //look for registered types first Object obj; if (null != (obj = mimeTypeAssociations.get(mimeType))) { ScriptEngineFactory spi = (ScriptEngineFactory) obj; try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } for (ScriptEngineFactory spi : engineSpis) { List<String> types = null; try { types = spi.getMimeTypes(); } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } if (types == null) continue; for (String type : types) { if (mimeType.equals(type)) { try { ScriptEngine engine = spi.getScriptEngine(); engine.setBindings(getBindings(), ScriptContext.GLOBAL_SCOPE); return engine; } catch (Exception exp) { if (DEBUG) exp.printStackTrace(); } } } } return null; } /** * Returns a list whose elements are instances of all the <code>ScriptEngineFactory</code> classes * found by the discovery mechanism. * @return List of all discovered <code>ScriptEngineFactory</code>s. */ public List<ScriptEngineFactory> getEngineFactories() { List<ScriptEngineFactory> res = new ArrayList<ScriptEngineFactory>(engineSpis.size()); for (ScriptEngineFactory spi : engineSpis) { res.add(spi); } return Collections.unmodifiableList(res); } /** * Registers a <code>ScriptEngineFactory</code> to handle a language * name. Overrides any such association found using the Discovery mechanism. * @param name The name to be associated with the <code>ScriptEngineFactory</code>. * @param factory The class to associate with the given name. * @throws NullPointerException if any of the parameters is null. */ public void registerEngineName(String name, ScriptEngineFactory factory) { if (name == null || factory == null) throw new NullPointerException(); nameAssociations.put(name, factory); } /** * Registers a <code>ScriptEngineFactory</code> to handle a mime type. * Overrides any such association found using the Discovery mechanism. * * @param type The mime type to be associated with the * <code>ScriptEngineFactory</code>. * * @param factory The class to associate with the given mime type. * @throws NullPointerException if any of the parameters is null. */ public void registerEngineMimeType(String type, ScriptEngineFactory factory) { if (type == null || factory == null) throw new NullPointerException(); mimeTypeAssociations.put(type, factory); } /** * Registers a <code>ScriptEngineFactory</code> to handle an extension. * Overrides any such association found using the Discovery mechanism. * * @param extension The extension type to be associated with the * <code>ScriptEngineFactory</code>. * @param factory The class to associate with the given extension. * @throws NullPointerException if any of the parameters is null. */ public void registerEngineExtension(String extension, ScriptEngineFactory factory) { if (extension == null || factory == null) throw new NullPointerException(); extensionAssociations.put(extension, factory); } /** Set of script engine factories discovered. */ private TreeSet<ScriptEngineFactory> engineSpis; /** Map of engine name to script engine factory. */ private HashMap<String, ScriptEngineFactory> nameAssociations; /** Map of script file extension to script engine factory. */ private HashMap<String, ScriptEngineFactory> extensionAssociations; /** Map of script MIME type to script engine factory. */ private HashMap<String, ScriptEngineFactory> mimeTypeAssociations; /** Global bindings associated with script engines created by this manager. */ private Bindings globalScope; }