xml/validation/SchemaFactoryFinder.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.
 */
// $Id: SchemaFactoryFinder.java 727367 2008-12-17 13:05:26Z mrglavas $

package javax.xml.validation;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Properties;
import javax.xml.XMLConstants;
import libcore.io.IoUtils;

/**
 * Implementation of {@link SchemaFactory#newInstance(String)}.
 *
 * @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
 * @version $Revision: 727367 $, $Date: 2008-12-17 05:05:26 -0800 (Wed, 17 Dec 2008) $
 * @since 1.5
 */
final class SchemaFactoryFinder  {

    /** XML Schema language identifiers. */
    private static final String W3C_XML_SCHEMA10_NS_URI = "http://www.w3.org/XML/XMLSchema/v1.0";
    private static final String W3C_XML_SCHEMA11_NS_URI = "http://www.w3.org/XML/XMLSchema/v1.1";

    /** debug support code. */
    private static boolean debug = false;

    /**
     * <p>Cache properties for performance. Use a static class to avoid double-checked
     * locking.</p>
     */
    private static class CacheHolder {

        private static Properties cacheProps = new Properties();

        static {
            String javah = System.getProperty("java.home");
            String configFile = javah + File.separator + "lib" + File.separator + "jaxp.properties";
            File f = new File(configFile);
            if (f.exists()) {
                if (debug) debugPrintln("Read properties file " + f);
                try {
                    cacheProps.load(new FileInputStream(f));
                } catch (Exception ex) {
                    if (debug) {
                        ex.printStackTrace();
                    }
                }
            }
        }
    }

    /**
     * Default columns per line.
     */
    private static final int DEFAULT_LINE_LENGTH = 80;

    static {
        String val = System.getProperty("jaxp.debug");
        // Allow simply setting the prop to turn on debug
        debug = val != null && (! "false".equals(val));
    }

    /**
     * <p>Conditional debug printing.</p>
     *
     * @param msg to print
     */
    private static void debugPrintln(String msg) {
        if (debug) {
            System.err.println("JAXP: " + msg);
        }
    }

    /**
     * <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() {
        if (classLoader == Thread.currentThread().getContextClassLoader()) {
            debugPrintln("using thread context class loader ("+classLoader+") for search");
            return;
        }

        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 <tt>schemaLanguage</tt> parameter is null.
     */
    public SchemaFactory newFactory(String schemaLanguage) {
        if (schemaLanguage == null) {
            throw new NullPointerException("schemaLanguage == null");
        }
        SchemaFactory f = _newFactory(schemaLanguage);
        if (debug) {
            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 {
            if (debug) debugPrintln("Looking up system property '"+propertyName+"'" );
            String r = System.getProperty(propertyName);
            if (r != null && r.length() > 0) {
                if (debug) debugPrintln("The value is '"+r+"'");
                sf = createInstance(r);
                if(sf!=null)    return sf;
            }
            else if (debug) {
                debugPrintln("The property is undefined.");
            }
        }
        // The VM ran out of memory or there was some other serious problem. Re-throw.
        catch (VirtualMachineError vme) {
            throw vme;
        }
        // ThreadDeath should always be re-thrown
        catch (ThreadDeath td) {
            throw td;
        }
        catch (Throwable t) {
            if( debug ) {
                debugPrintln("failed to look up system property '"+propertyName+"'" );
                t.printStackTrace();
            }
        }

        // try to read from $java.home/lib/jaxp.properties
        try {
            String factoryClassName = CacheHolder.cacheProps.getProperty(propertyName);
            if (debug) debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");

            if (factoryClassName != null) {
                sf = createInstance(factoryClassName);
                if(sf != null){
                    return sf;
                }
            }
        } catch (Exception ex) {
            if (debug) {
                ex.printStackTrace();
            }
        }

        // try META-INF/services files
        for (URL resource : createServiceFileIterator()) {
            if (debug) debugPrintln("looking into " + resource);
            try {
                sf = loadFromServicesFile(schemaLanguage,resource.toExternalForm(),
                        resource.openStream());
                if(sf!=null)    return sf;
            } catch(IOException e) {
                if( debug ) {
                    debugPrintln("failed to read "+resource);
                    e.printStackTrace();
                }
            }
        }

        // platform defaults
        if (schemaLanguage.equals(XMLConstants.W3C_XML_SCHEMA_NS_URI) || schemaLanguage.equals(W3C_XML_SCHEMA10_NS_URI)) {
            if (debug) debugPrintln("attempting to use the platform default XML Schema 1.0 validator");
            return createInstance("org.apache.xerces.jaxp.validation.XMLSchemaFactory");
        }
        else if (schemaLanguage.equals(W3C_XML_SCHEMA11_NS_URI)) {
            if (debug) debugPrintln("attempting to use the platform default XML Schema 1.1 validator");
            return createInstance("org.apache.xerces.jaxp.validation.XMLSchema11Factory");
        }

        if (debug) debugPrintln("all things were tried, but none was found. bailing out.");
        return null;
    }

    /**
     * <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 ) {
        try {
            if (debug) debugPrintln("instantiating "+className);
            Class clazz;
            if( classLoader!=null )
                clazz = classLoader.loadClass(className);
            else
                clazz = Class.forName(className);
            if(debug)       debugPrintln("loaded it from "+which(clazz));
            Object o = clazz.newInstance();

            if( o instanceof SchemaFactory )
                return (SchemaFactory)o;

            if (debug) debugPrintln(className+" is not assignable to "+SERVICE_CLASS.getName());
        }
        // The VM ran out of memory or there was some other serious problem. Re-throw.
        catch (VirtualMachineError vme) {
            throw vme;
        }
        // ThreadDeath should always be re-thrown
        catch (ThreadDeath td) {
            throw td;
        }
        catch (Throwable t) {
            debugPrintln("failed to instantiate "+className);
            if(debug)   t.printStackTrace();
        }
        return null;
    }

    /**
     * Returns an {@link Iterator} that enumerates all
     * the META-INF/services files that we care.
     */
    private Iterable<URL> createServiceFileIterator() {
        if (classLoader == null) {
            ClassLoader classLoader = SchemaFactoryFinder.class.getClassLoader();
            return Collections.singleton(classLoader.getResource(SERVICE_ID));
        } else {
            try {
                Enumeration<URL> e = classLoader.getResources(SERVICE_ID);
                if (debug && !e.hasMoreElements()) {
                    debugPrintln("no "+SERVICE_ID+" file was found");
                }

                // wrap it into an Iterator.
                return Collections.list(e);
            } catch (IOException e) {
                if (debug) {
                    debugPrintln("failed to enumerate resources "+SERVICE_ID);
                    e.printStackTrace();
                }
                return Collections.emptySet();
            }
        }
    }

    /** Searches for a SchemaFactory for a given schema language in a META-INF/services file. */
    private SchemaFactory loadFromServicesFile(String schemaLanguage, String resourceName, InputStream in) {

        if (debug) debugPrintln("Reading "+resourceName );

        // Read the service provider name in UTF-8 as specified in
        // the jar spec.  Unfortunately this fails in Microsoft
        // VJ++, which does not implement the UTF-8
        // encoding. Theoretically, we should simply let it fail in
        // that case, since the JVM is obviously broken if it
        // doesn't support such a basic standard.  But since there
        // are still some users attempting to use VJ++ for
        // development, we have dropped in a fallback which makes a
        // second attempt using the platform's default encoding. In
        // VJ++ this is apparently ASCII, which is a subset of
        // UTF-8... and since the strings we'll be reading here are
        // also primarily limited to the 7-bit ASCII range (at
        // least, in English versions), this should work well
        // enough to keep us on the air until we're ready to
        // officially decommit from VJ++. [Edited comment from
        // jkesselm]
        BufferedReader rd;
        try {
            rd = new BufferedReader(new InputStreamReader(in, "UTF-8"), DEFAULT_LINE_LENGTH);
        } catch (java.io.UnsupportedEncodingException e) {
            rd = new BufferedReader(new InputStreamReader(in), DEFAULT_LINE_LENGTH);
        }

        String factoryClassName = null;
        SchemaFactory resultFactory = null;
        // See spec for provider-configuration files: http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Provider%20Configuration%20File
        while (true) {
            try {
                factoryClassName = rd.readLine();
            } catch (IOException x) {
                // No provider found
                break;
            }
            if (factoryClassName != null) {
                // Ignore comments in the provider-configuration file
                int hashIndex = factoryClassName.indexOf('#');
                if (hashIndex != -1) {
                    factoryClassName = factoryClassName.substring(0, hashIndex);
                }

                // Ignore leading and trailing whitespace
                factoryClassName = factoryClassName.trim();

                // If there's no text left or if this was a blank line, go to the next one.
                if (factoryClassName.length() == 0) {
                    continue;
                }

                try {
                    // Found the right SchemaFactory if its isSchemaLanguageSupported(schemaLanguage) method returns true.
                    SchemaFactory foundFactory = (SchemaFactory) createInstance(factoryClassName);
                    if (foundFactory.isSchemaLanguageSupported(schemaLanguage)) {
                        resultFactory = foundFactory;
                        break;
                    }
                }
                catch (Exception ignored) {}
            }
            else {
                break;
            }
        }

        IoUtils.closeQuietly(rd);

        return resultFactory;
    }

    private static final Class SERVICE_CLASS = SchemaFactory.class;
    private static final String SERVICE_ID = "META-INF/services/" + SERVICE_CLASS.getName();

    private static String which( Class clazz ) {
        return which( clazz.getName(), clazz.getClassLoader() );
    }

    /**
     * <p>Search the specified classloader for the given classname.</p>
     *
     * @param classname the fully qualified name of the class to search for
     * @param loader the classloader to search
     *
     * @return the source location of the resource, or null if it wasn't found
     */
    private static String which(String classname, ClassLoader loader) {
        String classnameAsResource = classname.replace('.', '/') + ".class";

        if (loader == null)  loader = ClassLoader.getSystemClassLoader();

        URL it = loader.getResource(classnameAsResource);
        return it != null ? it.toString() : null;
    }
}