objectfactory.java

java1.6众多例子参考

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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: ObjectFactory.java,v 1.1.2.1 2005/08/01 01:30:35 jeffsuttor Exp $
 */

package com.sun.org.apache.xpath.internal.compiler;

import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileInputStream;

import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;

/**
 * This class is duplicated for each JAXP subpackage so keep it in sync.
 * It is package private and therefore is not exposed as part of the JAXP
 * API.
 * <p>
 * This code is designed to implement the JAXP 1.1 spec pluggability
 * feature and is designed to run on JDK version 1.1 and
 * later, and to compile on JDK 1.2 and onward.
 * The code also runs both as part of an unbundled jar file and
 * when bundled as part of the JDK.
 * <p>
 * This class was moved from the <code>javax.xml.parsers.ObjectFactory</code>
 * class and modified to be used as a general utility for creating objects
 * dynamically.
 *
 * @version $Id: ObjectFactory.java,v 1.1.2.1 2005/08/01 01:30:35 jeffsuttor Exp $
 */
class ObjectFactory {

    //
    // Constants
    //

    // name of default properties file to look for in JDK's jre/lib directory
    private static final String DEFAULT_PROPERTIES_FILENAME =
                                                     "xalan.properties";

    private static final String SERVICES_PATH = "META-INF/services/";

    /** Set to true for debugging */
    private static final boolean DEBUG = false;

    /** cache the contents of the xalan.properties file.
     *  Until an attempt has been made to read this file, this will
     * be null; if the file does not exist or we encounter some other error
     * during the read, this will be empty.
     */
    private static Properties fXalanProperties = null;

    /***
     * Cache the time stamp of the xalan.properties file so
     * that we know if it's been modified and can invalidate
     * the cache when necessary.
     */
    private static long fLastModified = -1;

    //
    // Public static methods
    //

    /**
     * Finds the implementation Class object in the specified order.  The
     * specified order is the following:
     * <ol>
     *  <li>query the system property using <code>System.getProperty</code>
     *  <li>read <code>META-INF/services/<i>factoryId</i></code> file
     *  <li>use fallback classname
     * </ol>
     *
     * @return instance of factory, never null
     *
     * @param factoryId             Name of the factory to find, same as
     *                              a property name
     * @param fallbackClassName     Implementation class name, if nothing else
     *                              is found.  Use null to mean no fallback.
     *
     * @exception ObjectFactory.ConfigurationError
     */
    static Object createObject(String factoryId, String fallbackClassName)
        throws ConfigurationError {
        return createObject(factoryId, null, fallbackClassName);
    } // createObject(String,String):Object

    /**
     * Finds the implementation Class object in the specified order.  The
     * specified order is the following:
     * <ol>
     *  <li>query the system property using <code>System.getProperty</code>
     *  <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
     *  <li>read <code>META-INF/services/<i>factoryId</i></code> file
     *  <li>use fallback classname
     * </ol>
     *
     * @return instance of factory, never null
     *
     * @param factoryId             Name of the factory to find, same as
     *                              a property name
     * @param propertiesFilename The filename in the $java.home/lib directory
     *                           of the properties file.  If none specified,
     *                           ${java.home}/lib/xalan.properties will be used.
     * @param fallbackClassName     Implementation class name, if nothing else
     *                              is found.  Use null to mean no fallback.
     *
     * @exception ObjectFactory.ConfigurationError
     */
    static Object createObject(String factoryId,
                                      String propertiesFilename,
                                      String fallbackClassName)
        throws ConfigurationError
    {
        Class factoryClass = lookUpFactoryClass(factoryId,
                                                propertiesFilename,
                                                fallbackClassName);

        if (factoryClass == null) {
            throw new ConfigurationError(
                "Provider for " + factoryId + " cannot be found", null);
        }

        try{
            Object instance = factoryClass.newInstance();
            debugPrintln("created new instance of factory " + factoryId);
            return instance;
        } catch (Exception x) {
            throw new ConfigurationError(
                "Provider for factory " + factoryId
                    + " could not be instantiated: " + x, x);
        }
    } // createObject(String,String,String):Object

    /**
     * Finds the implementation Class object in the specified order.  The
     * specified order is the following:
     * <ol>
     *  <li>query the system property using <code>System.getProperty</code>
     *  <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
     *  <li>read <code>META-INF/services/<i>factoryId</i></code> file
     *  <li>use fallback classname
     * </ol>
     *
     * @return Class object of factory, never null
     *
     * @param factoryId             Name of the factory to find, same as
     *                              a property name
     * @param propertiesFilename The filename in the $java.home/lib directory
     *                           of the properties file.  If none specified,
     *                           ${java.home}/lib/xalan.properties will be used.
     * @param fallbackClassName     Implementation class name, if nothing else
     *                              is found.  Use null to mean no fallback.
     *
     * @exception ObjectFactory.ConfigurationError
     */
    static Class lookUpFactoryClass(String factoryId)
        throws ConfigurationError
    {
        return lookUpFactoryClass(factoryId, null, null);
    } // lookUpFactoryClass(String):Class

    /**
     * Finds the implementation Class object in the specified order.  The
     * specified order is the following:
     * <ol>
     *  <li>query the system property using <code>System.getProperty</code>
     *  <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
     *  <li>read <code>META-INF/services/<i>factoryId</i></code> file
     *  <li>use fallback classname
     * </ol>
     *
     * @return Class object that provides factory service, never null
     *
     * @param factoryId             Name of the factory to find, same as
     *                              a property name
     * @param propertiesFilename The filename in the $java.home/lib directory
     *                           of the properties file.  If none specified,
     *                           ${java.home}/lib/xalan.properties will be used.
     * @param fallbackClassName     Implementation class name, if nothing else
     *                              is found.  Use null to mean no fallback.
     *
     * @exception ObjectFactory.ConfigurationError
     */
    static Class lookUpFactoryClass(String factoryId,
                                           String propertiesFilename,
                                           String fallbackClassName)
        throws ConfigurationError
    {
        String factoryClassName = lookUpFactoryClassName(factoryId,
                                                         propertiesFilename,
                                                         fallbackClassName);
        ClassLoader cl = findClassLoader();

        if (factoryClassName == null) {
            factoryClassName = fallbackClassName;
        }

        // assert(className != null);
        try{
            Class providerClass = findProviderClass(factoryClassName,
                                                    cl,
                                                    true);
            debugPrintln("created new instance of " + providerClass +
                   " using ClassLoader: " + cl);
            return providerClass;
        } catch (ClassNotFoundException x) {
            throw new ConfigurationError(
                "Provider " + factoryClassName + " not found", x);
        } catch (Exception x) {
            throw new ConfigurationError(
                "Provider "+factoryClassName+" could not be instantiated: "+x,
                x);
        }
    } // lookUpFactoryClass(String,String,String):Class

    /**
     * Finds the name of the required implementation class in the specified
     * order.  The specified order is the following:
     * <ol>
     *  <li>query the system property using <code>System.getProperty</code>
     *  <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
     *  <li>read <code>META-INF/services/<i>factoryId</i></code> file
     *  <li>use fallback classname
     * </ol>
     *
     * @return name of class that provides factory service, never null
     *
     * @param factoryId             Name of the factory to find, same as
     *                              a property name
     * @param propertiesFilename The filename in the $java.home/lib directory
     *                           of the properties file.  If none specified,
     *                           ${java.home}/lib/xalan.properties will be used.
     * @param fallbackClassName     Implementation class name, if nothing else
     *                              is found.  Use null to mean no fallback.
     *
     * @exception ObjectFactory.ConfigurationError
     */
    static String lookUpFactoryClassName(String factoryId,
                                                String propertiesFilename,
                                                String fallbackClassName)
    {
        SecuritySupport ss = SecuritySupport.getInstance();

        // Use the system property first
        try {
            String systemProp = ss.getSystemProperty(factoryId);
            if (systemProp != null) {
                debugPrintln("found system property, value=" + systemProp);
                return systemProp;
            }
        } catch (SecurityException se) {
            // Ignore and continue w/ next location
        }

        // Try to read from propertiesFilename, or
        // $java.home/lib/xalan.properties
        String factoryClassName = null;
        // no properties file name specified; use
        // $JAVA_HOME/lib/xalan.properties:
        if (propertiesFilename == null) {
            File propertiesFile = null;
            boolean propertiesFileExists = false;
            try {
                String javah = ss.getSystemProperty("java.home");
                propertiesFilename = javah + File.separator +
                    "lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
                propertiesFile = new File(propertiesFilename);
                propertiesFileExists = ss.getFileExists(propertiesFile);
            } catch (SecurityException e) {
                // try again...
                fLastModified = -1;
                fXalanProperties = null;
            }

            synchronized (ObjectFactory.class) {
                boolean loadProperties = false;
                try {
                    // file existed last time
                    if(fLastModified >= 0) {
                        if(propertiesFileExists &&
                                (fLastModified < (fLastModified = ss.getLastModified(propertiesFile)))) {
                            loadProperties = true;
                        } else {
                            // file has stopped existing...
                            if(!propertiesFileExists) {
                                fLastModified = -1;
                                fXalanProperties = null;
                            } // else, file wasn't modified!
                        }
                    } else {
                        // file has started to exist:
                        if(propertiesFileExists) {
                            loadProperties = true;
                            fLastModified = ss.getLastModified(propertiesFile);
                        } // else, nothing's changed
                    }
                    if(loadProperties) {
                        // must never have attempted to read xalan.properties
                        // before (or it's outdeated)