Java example source code file (ScriptEngineManager.java)

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Java - Java tags/keywords

bindings, classloader, debug, exception, hashmap, hashset, list, nullpointerexception, object, scriptengine, scriptenginefactory, scriptenginemanager, security, serviceconfigurationerror, string, util

The ScriptEngineManager.java Java example source code

/*
 * 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 implements a discovery and instantiation
 * mechanism for <code>ScriptEngine classes and also maintains a
 * collection of key/value pairs storing state shared by all engines created
 * by the Manager. This class uses the <a href="../../../technotes/guides/jar/jar.html#Service%20Provider">service provider mechanism to enumerate all the
 * implementations of <code>ScriptEngineFactory. 


 * The <code>ScriptEngineManager 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 of key/value pairs, referred to as the "Global Scope"  maintained
 * by the manager is available to all instances of <code>ScriptEngine created
 * by the <code>ScriptEngineManager.  The values in the Bindings 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()).
     *
     * @see java.lang.Thread#getContextClassLoader
     */
    public ScriptEngineManager() {
        ClassLoader ctxtLoader = Thread.currentThread().getContextClassLoader();
        init(ctxtLoader);
    }

    /**
     * This constructor loads the implementations of
     * <code>ScriptEngineFactory visible to the given
     * <code>ClassLoader using the service provider mechanism.


     * If loader is <code>null, the script engine factories that are
     * bundled with the platform and that are in the usual extension
     * directories (installed extensions) 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 HashSet<ScriptEngineFactory>();
        nameAssociations = new HashMap<String, ScriptEngineFactory>();
        extensionAssociations = new HashMap<String, ScriptEngineFactory>();
        mimeTypeAssociations = new HashMap<String, ScriptEngineFactory>();
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            public Object run() {
                initEngines(loader);
                return null;
            }
        });
    }

    private void initEngines(final ClassLoader loader) {
        Iterator<ScriptEngineFactory> itr = null;
        try {
            ServiceLoader<ScriptEngineFactory> sl;
            if (loader != null) {
                sl = ServiceLoader.load(ScriptEngineFactory.class, loader);
            } else {
                sl = ServiceLoader.loadInstalled(ScriptEngineFactory.class);
            }
            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 stores the specified Bindings
     * in the <code>globalScope field. ScriptEngineManager sets this
     * <code>Bindings as global bindings for ScriptEngine
     * objects created by it.
     *
     * @param bindings The specified <code>Bindings
     * @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 returns the value of the globalScope field.
     * ScriptEngineManager sets this <code>Bindings as global bindings for
     * <code>ScriptEngine 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 for a given  name.
     * The algorithm first searches for a <code>ScriptEngineFactory that has been
     * registered as a handler for the specified name using the <code>registerEngineName
     * method.
     * <br>
 If one is not found, it searches the set of ScriptEngineFactory instances
     * stored by the constructor for one with the specified name.  If a <code>ScriptEngineFactory
     * is found by either method, it is used to create instance of <code>ScriptEngine.
     * @param shortName The short name of the <code>ScriptEngine implementation.
     * returned by the <code>getNames method of its ScriptEngineFactory.
     * @return A <code>ScriptEngine created by the factory located in the search.  Returns null
     * if no such factory was found.  The <code>ScriptEngineManager sets its own globalScope
     * <code>Bindings as the GLOBAL_SCOPE Bindings of the newly
     * created <code>ScriptEngine.
     * @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 for a given extension.  The algorithm
     * used by <code>getEngineByName is used except that the search starts
     * by looking for a <code>ScriptEngineFactory registered to handle the
     * given extension using <code>registerEngineExtension.
     * @param extension The given extension
     * @return The engine to handle scripts with this extension.  Returns <code>null
     * 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 for a given mime type.  The algorithm
     * used by <code>getEngineByName is used except that the search starts
     * by looking for a <code>ScriptEngineFactory registered to handle the
     * given mime type using <code>registerEngineMimeType.
     * @param mimeType The given mime type
     * @return The engine to handle scripts with this mime type.  Returns <code>null
     * 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 classes
     * found by the discovery mechanism.
     * @return List of all discovered <code>ScriptEngineFactorys.
     */
    public List<ScriptEngineFactory> getEngineFactories() {
        List<ScriptEngineFactory> res = new ArrayList(engineSpis.size());
        for (ScriptEngineFactory spi : engineSpis) {
            res.add(spi);
        }
        return Collections.unmodifiableList(res);
    }

    /**
     * Registers a <code>ScriptEngineFactory 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.
     * @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 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.
     *
     * @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 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.
     * @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 HashSet<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 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;
}