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 * Copyright (c) 2003, 2017, 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

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package javax.xml.validation;

import java.io.File;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Properties;

import java.util.ServiceConfigurationError;

import java.util.ServiceLoader;

import java.util.function.Supplier;

/**

 * Implementation of {@link SchemaFactory#newInstance(String)}.

 *

 * @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>

 * @since 1.5

 */

class SchemaFactoryFinder  {

    /** debug support code. */

    private static boolean debug = false;

    /**

     *<p> Take care of restrictions imposed by java security model </p>

     */

    private static final SecuritySupport ss = new SecuritySupport();

    private static final String DEFAULT_PACKAGE = "com.sun.org.apache.xerces.internal";

    /**

     * <p>Cache properties for performance.</p>

     */

    private static final Properties cacheProps = new Properties();

    /**

     * <p>First time requires initialization overhead.</p>

     */

    private static volatile boolean firstTime = true;

    static {

        // Use try/catch block to support applets

        try {

            debug = ss.getSystemProperty("jaxp.debug") != null;

        } catch (Exception unused) {

            debug = false;

        }

    }

    /**

     * <p>Conditional debug printing.</p>

     *

     * @param msgGen Supplier function that returns debug message

     */

    private static void debugPrintln(Supplier<String> msgGen) {

        if (debug) {

            System.err.println("JAXP: " + msgGen.get());

        }

    }

    /**

     * <p><code>ClassLoader</code> to use to find <code>SchemaFactory</code>.</p>

     */

    private final ClassLoader classLoader;

    /**

     * <p>Constructor that specifies <code>ClassLoader</code> to use

     * to find <code>SchemaFactory</code>.</p>

     *

     * @param loader

     *      to be used to load resource, {@link SchemaFactory}, and

     *      {@link SchemaFactoryLoader} implementations during

     *      the resolution process.

     *      If this parameter is null, the default system class loader

     *      will be used.

     */

    public SchemaFactoryFinder(ClassLoader loader) {

        this.classLoader = loader;

        if( debug ) {

            debugDisplayClassLoader();

        }

    }

    private void debugDisplayClassLoader() {

        try {

            if( classLoader == ss.getContextClassLoader() ) {

                debugPrintln(()->"using thread context class loader ("+classLoader+") for search");

                return;

            }

        } catch( Throwable unused ) {

            // getContextClassLoader() undefined in JDK1.1

        }

        if( classLoader==ClassLoader.getSystemClassLoader() ) {

            debugPrintln(()->"using system class loader ("+classLoader+") for search");

            return;

        }

        debugPrintln(()->"using class loader ("+classLoader+") for search");

    }

    /**

     * <p>Creates a new {@link SchemaFactory} object for the specified

     * schema language.</p>

     *

     * @param schemaLanguage

     *      See {@link SchemaFactory Schema Language} table in <code>SchemaFactory</code>

     *      for the list of available schema languages.

     *

     * @return <code>null</code> if the callee fails to create one.

     *

     * @throws NullPointerException

     *      If the <code>schemaLanguage</code> parameter is null.

     * @throws SchemaFactoryConfigurationError

     *      If a configuration error is encountered.

     */

    public SchemaFactory newFactory(String schemaLanguage) {

        if(schemaLanguage==null) {

            throw new NullPointerException();

        }

        SchemaFactory f = _newFactory(schemaLanguage);

        if (f != null) {

            debugPrintln(()->"factory '" + f.getClass().getName() + "' was found for " + schemaLanguage);

        } else {

            debugPrintln(()->"unable to find a factory for " + schemaLanguage);

        }

        return f;

    }

    /**

     * <p>Lookup a <code>SchemaFactory</code> for the given <code>schemaLanguage</code>.</p>

     *

     * @param schemaLanguage Schema language to lookup <code>SchemaFactory</code> for.

     *

     * @return <code>SchemaFactory</code> for the given <code>schemaLanguage</code>.

     */

    private SchemaFactory _newFactory(String schemaLanguage) {

        SchemaFactory sf;

        String propertyName = SERVICE_CLASS.getName() + ":" + schemaLanguage;

        // system property look up

        try {

            debugPrintln(()->"Looking up system property '"+propertyName+"'" );

            String r = ss.getSystemProperty(propertyName);

            if(r!=null) {

                debugPrintln(()->"The value is '"+r+"'");

                sf = createInstance(r, true);

                if(sf!=null)    return sf;

            } else

                debugPrintln(()->"The property is undefined.");

        } catch( Throwable t ) {

            if( debug ) {

                debugPrintln(()->"failed to look up system property '"+propertyName+"'" );

                t.printStackTrace();

            }

        }

        String javah = ss.getSystemProperty( "java.home" );

        String configFile = javah + File.separator +

        "conf" + File.separator + "jaxp.properties";

        // try to read from $java.home/conf/jaxp.properties

        try {

            if(firstTime){

                synchronized(cacheProps){

                    if(firstTime){

                        File f=new File( configFile );

                        firstTime = false;

                        if(ss.doesFileExist(f)){

                            debugPrintln(()->"Read properties file " + f);

                            cacheProps.load(ss.getFileInputStream(f));

                        }

                    }

                }

            }

            final String factoryClassName = cacheProps.getProperty(propertyName);

            debugPrintln(()->"found " + factoryClassName + " in $java.home/conf/jaxp.properties");

            if (factoryClassName != null) {

                sf = createInstance(factoryClassName, true);

                if(sf != null){

                    return sf;

                }

            }

        } catch (Exception ex) {

            if (debug) {

                ex.printStackTrace();

            }

        }

        // Try with ServiceLoader

        final SchemaFactory factoryImpl = findServiceProvider(schemaLanguage);

        // The following assertion should always be true.

        // Uncomment it, recompile, and run with -ea in case of doubts:

        // assert factoryImpl == null || factoryImpl.isSchemaLanguageSupported(schemaLanguage);

        if (factoryImpl != null) {

            return factoryImpl;

        }

        // platform default

        if(schemaLanguage.equals("http://www.w3.org/2001/XMLSchema")) {

            debugPrintln(()->"attempting to use the platform default XML Schema validator");

            return createInstance("com.sun.org.apache.xerces.internal.jaxp.validation.XMLSchemaFactory", true);

        }

        debugPrintln(()->"all things were tried, but none was found. bailing out.");

        return null;

    }

    /** <p>Create class using appropriate ClassLoader.</p>

     *

     * @param className Name of class to create.

     * @return Created class or <code>null</code>.

     */

    private Class<?> createClass(String className) {

        Class<?> clazz;

        // make sure we have access to restricted packages

        boolean internal = false;

        if (System.getSecurityManager() != null) {

            if (className != null && className.startsWith(DEFAULT_PACKAGE)) {

                internal = true;

            }

        }

        try {

            if (classLoader != null && !internal) {

                clazz = Class.forName(className, false, classLoader);

            } else {

                clazz = Class.forName(className);

            }

        } catch (Throwable t) {

            if(debug)  {

                t.printStackTrace();

            }

            return null;

        }

        return clazz;

    }

    /**

     * <p>Creates an instance of the specified and returns it.</p>

     *

     * @param className

     *      fully qualified class name to be instantiated.

     *

     * @return null

     *      if it fails. Error messages will be printed by this method.

     */

    SchemaFactory createInstance( String className ) {

        return createInstance( className, false );

    }

    SchemaFactory createInstance( String className, boolean useServicesMechanism ) {

        SchemaFactory schemaFactory = null;

        debugPrintln(()->"createInstance(" + className + ")");

        // get Class from className

        Class<?> clazz = createClass(className);

        if (clazz == null) {

            debugPrintln(()->"failed to getClass(" + className + ")");

            return null;

        }

        debugPrintln(()->"loaded " + className + " from " + which(clazz));

        // instantiate Class as a SchemaFactory

        try {

            if (!SchemaFactory.class.isAssignableFrom(clazz)) {

                throw new ClassCastException(clazz.getName()

                            + " cannot be cast to " + SchemaFactory.class);

            }

            if (!useServicesMechanism) {

                schemaFactory = newInstanceNoServiceLoader(clazz);

            }

            if (schemaFactory == null) {

                schemaFactory = (SchemaFactory) clazz.getConstructor().newInstance();

            }

        } catch (ClassCastException | IllegalAccessException | IllegalArgumentException |

            InstantiationException | InvocationTargetException | NoSuchMethodException |

            SecurityException ex) {

            debugPrintln(()->"could not instantiate " + clazz.getName());

            if (debug) {

                    ex.printStackTrace();

            }

            return null;

        }

        return schemaFactory;

    }

    /**

     * Try to construct using newXMLSchemaFactoryNoServiceLoader

     *   method if available.

     */

    private static SchemaFactory newInstanceNoServiceLoader(

         Class<?> providerClass

    ) {

        // Retain maximum compatibility if no security manager.

        if (System.getSecurityManager() == null) {

            return null;

        }

        try {

            final Method creationMethod =

                providerClass.getDeclaredMethod(

                    "newXMLSchemaFactoryNoServiceLoader"

                );

            final int modifiers = creationMethod.getModifiers();

            // Do not call the method if it's not public static.

            if (!Modifier.isStatic(modifiers) || !Modifier.isPublic(modifiers)) {

                return null;

            }

            // Only calls "newXMLSchemaFactoryNoServiceLoader" if it's

            // declared to return an instance of SchemaFactory.

            final Class<?> returnType = creationMethod.getReturnType();

            if (SERVICE_CLASS.isAssignableFrom(returnType)) {

                return SERVICE_CLASS.cast(creationMethod.invoke(null, (Object[])null));

            } else {

                // Should not happen since

                // XMLSchemaFactory.newXMLSchemaFactoryNoServiceLoader is

                // declared to return XMLSchemaFactory.

                throw new ClassCastException(returnType

                            + " cannot be cast to " + SERVICE_CLASS);

            }

        } catch(ClassCastException e) {

            throw new SchemaFactoryConfigurationError(e.getMessage(), e);

        } catch (NoSuchMethodException exc) {

            return null;

        } catch (Exception exc) {

            return null;

        }

    }

    // Call isSchemaLanguageSupported with initial context.

    private boolean isSchemaLanguageSupportedBy(final SchemaFactory factory,

            final String schemaLanguage,

            AccessControlContext acc) {

        return AccessController.doPrivileged(new PrivilegedAction<Boolean>() {

            public Boolean run() {

                return factory.isSchemaLanguageSupported(schemaLanguage);

            }

        }, acc);

    }

    /**

     * Finds a service provider subclass of SchemaFactory that supports the

     * given schema language using the ServiceLoader.

     *

     * @param schemaLanguage The schema language for which we seek a factory.

     * @return A SchemaFactory supporting the specified schema language, or null

     *         if none is found.

     * @throws SchemaFactoryConfigurationError if a configuration error is found.

     */

    private SchemaFactory findServiceProvider(final String schemaLanguage) {

        assert schemaLanguage != null;

        // store current context.

        final AccessControlContext acc = AccessController.getContext();

        try {

            return AccessController.doPrivileged(new PrivilegedAction<SchemaFactory>() {

                public SchemaFactory run() {

                    final ServiceLoader<SchemaFactory> loader =

                            ServiceLoader.load(SERVICE_CLASS);

                    for (SchemaFactory factory : loader) {

                        // restore initial context to call

                        // factory.isSchemaLanguageSupported

                        if (isSchemaLanguageSupportedBy(factory, schemaLanguage, acc)) {

                            return factory;

                        }

                    }

                    return null; // no factory found.

                }

            });

        } catch (ServiceConfigurationError error) {

            throw new SchemaFactoryConfigurationError(

                    "Provider for " + SERVICE_CLASS + " cannot be created", error);

        }

    }

    private static final Class<SchemaFactory> SERVICE_CLASS = SchemaFactory.class;

    // Used for debugging purposes

    private static String which( Class<?> clazz ) {

        return ss.getClassSource(clazz);

    }

}