objectfactory.java

java1.6众多例子参考

/*
 * Copyright 2001-2005 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.
 */

package com.sun.org.apache.xerces.internal.impl.dv;

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>
 * 
 * @xerces.internal 
 *
 * @version $Id: ObjectFactory.java,v 1.3 2005/09/26 13:02:19 sunithareddy Exp $
 */
final class ObjectFactory {

    //
    // Constants
    //

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

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

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

    /** cache the contents of the xerces.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 fXercesProperties = null;

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

    //
    // 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 Class object 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 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/xerces.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
    {
        if (DEBUG) debugPrintln("debug is on");

        SecuritySupport ss = SecuritySupport.getInstance();
        ClassLoader cl = findClassLoader();

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

        // JAXP specific change
        // always use fallback class to avoid the expense of constantly
        // "stat"ing a non-existent "xerces.properties" and jar SPI entry
        // see CR 6400863: Expensive creating of SAX parser in Mustang
        if (true) {
            if (fallbackClassName == null) {
                throw new ConfigurationError(
                    "Provider for " + factoryId + " cannot be found", null);
            }

            if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
            return newInstance(fallbackClassName, cl, true);
        }

        // Try to read from propertiesFilename, or $java.home/lib/xerces.properties
        String factoryClassName = null;
        // no properties file name specified; use $JAVA_HOME/lib/xerces.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;
                fXercesProperties = null;
            }
            
            synchronized (ObjectFactory.class) {
                boolean loadProperties = false;
                FileInputStream fis = null;
                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;
                                fXercesProperties = 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 xerces.properties before (or it's outdeated)
                        fXercesProperties = new Properties();
                        fis = ss.getFileInputStream(propertiesFile);
                        fXercesProperties.load(fis);
                    }
                } catch (Exception x) {
                    fXercesProperties = null;
                    fLastModified = -1;
                    // assert(x instanceof FileNotFoundException
                    //        || x instanceof SecurityException)
                    // In both cases, ignore and continue w/ next location
                }
                finally {
                    // try to close the input stream if one was opened.
                    if (fis != null) {
                        try {
                            fis.close();
                        }
                        // Ignore the exception.
                        catch (IOException exc) {}
                    }
                }
            }
            if(fXercesProperties != null) {
                factoryClassName = fXercesProperties.getProperty(factoryId);
            }
        } else {
            FileInputStream fis = null;
            try {
                fis = ss.getFileInputStream(new File(propertiesFilename));
                Properties props = new Properties();
                props.load(fis);
                factoryClassName = props.getProperty(factoryId);
            } catch (Exception x) {
                // assert(x instanceof FileNotFoundException
                //        || x instanceof SecurityException)
                // In both cases, ignore and continue w/ next location
            }
            finally {
                // try to close the input stream if one was opened.
                if (fis != null) {
                    try {
                        fis.close();
                    }
                    // Ignore the exception.
                    catch (IOException exc) {}
                }
            }
        }
        if (factoryClassName != null) {
            if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
            return newInstance(factoryClassName, cl, true);
        }

        // Try Jar Service Provider Mechanism
        Object provider = findJarServiceProvider(factoryId);
        if (provider != null) {
            return provider;
        }

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

        if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
        return newInstance(fallbackClassName, cl, true);
    } // createObject(String,String,String):Object

    //
    // Private static methods
    //

    /** Prints a message to standard error if debugging is enabled. */
    private static void debugPrintln(String msg) {
        if (DEBUG) {
            System.err.println("JAXP: " + msg);