546 lines
20 KiB
Java
546 lines
20 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.html.dom;
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import java.io.BufferedReader;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.util.Properties;
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/**
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* This class is duplicated for each JAXP subpackage so keep it in sync.
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* It is package private and therefore is not exposed as part of the JAXP
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* API.
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* <p>
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* This code is designed to implement the JAXP 1.1 spec pluggability
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* feature and is designed to run on JDK version 1.1 and
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* later, and to compile on JDK 1.2 and onward.
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* The code also runs both as part of an unbundled jar file and
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* when bundled as part of the JDK.
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* <p>
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*
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* @xerces.internal
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*
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* @version $Id$
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*/
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final class ObjectFactory {
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//
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// Constants
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//
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// name of default properties file to look for in JDK's jre/lib directory
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private static final String DEFAULT_PROPERTIES_FILENAME = "xerces.properties";
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/** Set to true for debugging */
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private static final boolean DEBUG = isDebugEnabled();
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/**
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* Default columns per line.
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*/
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private static final int DEFAULT_LINE_LENGTH = 80;
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/** cache the contents of the xerces.properties file.
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* Until an attempt has been made to read this file, this will
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* be null; if the file does not exist or we encounter some other error
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* during the read, this will be empty.
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*/
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private static Properties fXercesProperties = null;
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/***
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* Cache the time stamp of the xerces.properties file so
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* that we know if it's been modified and can invalidate
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* the cache when necessary.
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*/
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private static long fLastModified = -1;
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//
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// static methods
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//
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/**
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* Finds the implementation Class object in the specified order. The
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* specified order is the following:
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* <ol>
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* <li>query the system property using <code>System.getProperty</code>
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* <li>read <code>META-INF/services/<i>factoryId</i></code> file
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* <li>use fallback classname
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* </ol>
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*
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* @return Class object of factory, never null
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*
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* @param factoryId Name of the factory to find, same as
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* a property name
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* @param fallbackClassName Implementation class name, if nothing else
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* is found. Use null to mean no fallback.
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*
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* @exception ObjectFactory.ConfigurationError
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*/
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static Object createObject(String factoryId, String fallbackClassName)
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throws ConfigurationError {
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return createObject(factoryId, null, fallbackClassName);
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} // createObject(String,String):Object
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/**
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* Finds the implementation Class object in the specified order. The
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* specified order is the following:
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* <ol>
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* <li>query the system property using <code>System.getProperty</code>
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* <li>read <code>$java.home/lib/<i>propertiesFilename</i></code> file
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* <li>read <code>META-INF/services/<i>factoryId</i></code> file
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* <li>use fallback classname
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* </ol>
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*
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* @return Class object of factory, never null
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*
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* @param factoryId Name of the factory to find, same as
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* a property name
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* @param propertiesFilename The filename in the $java.home/lib directory
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* of the properties file. If none specified,
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* ${java.home}/lib/xerces.properties will be used.
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* @param fallbackClassName Implementation class name, if nothing else
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* is found. Use null to mean no fallback.
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*
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* @exception ObjectFactory.ConfigurationError
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*/
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static Object createObject(String factoryId,
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String propertiesFilename,
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String fallbackClassName)
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throws ConfigurationError
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{
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if (DEBUG) debugPrintln("debug is on");
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ClassLoader cl = findClassLoader();
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// Use the system property first
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try {
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String systemProp = SecuritySupport.getSystemProperty(factoryId);
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if (systemProp != null && systemProp.length() > 0) {
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if (DEBUG) debugPrintln("found system property, value=" + systemProp);
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return newInstance(systemProp, cl, true);
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}
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} catch (SecurityException se) {
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// Ignore and continue w/ next location
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}
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// Try to read from propertiesFilename, or $java.home/lib/xerces.properties
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String factoryClassName = null;
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// no properties file name specified; use $JAVA_HOME/lib/xerces.properties:
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if (propertiesFilename == null) {
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File propertiesFile = null;
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boolean propertiesFileExists = false;
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try {
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String javah = SecuritySupport.getSystemProperty("java.home");
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propertiesFilename = javah + File.separator +
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"lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
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propertiesFile = new File(propertiesFilename);
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propertiesFileExists = SecuritySupport.getFileExists(propertiesFile);
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} catch (SecurityException e) {
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// try again...
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fLastModified = -1;
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fXercesProperties = null;
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}
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synchronized (ObjectFactory.class) {
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boolean loadProperties = false;
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FileInputStream fis = null;
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try {
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// file existed last time
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if(fLastModified >= 0) {
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if(propertiesFileExists &&
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(fLastModified < (fLastModified = SecuritySupport.getLastModified(propertiesFile)))) {
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loadProperties = true;
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} else {
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// file has stopped existing...
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if(!propertiesFileExists) {
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fLastModified = -1;
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fXercesProperties = null;
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} // else, file wasn't modified!
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}
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} else {
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// file has started to exist:
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if(propertiesFileExists) {
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loadProperties = true;
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fLastModified = SecuritySupport.getLastModified(propertiesFile);
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} // else, nothing's changed
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}
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if(loadProperties) {
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// must never have attempted to read xerces.properties before (or it's outdeated)
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fXercesProperties = new Properties();
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fis = SecuritySupport.getFileInputStream(propertiesFile);
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fXercesProperties.load(fis);
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}
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} catch (Exception x) {
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fXercesProperties = null;
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fLastModified = -1;
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// assert(x instanceof FileNotFoundException
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// || x instanceof SecurityException)
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// In both cases, ignore and continue w/ next location
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}
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finally {
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// try to close the input stream if one was opened.
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if (fis != null) {
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try {
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fis.close();
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}
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// Ignore the exception.
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catch (IOException exc) {}
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}
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}
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}
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if(fXercesProperties != null) {
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factoryClassName = fXercesProperties.getProperty(factoryId);
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}
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} else {
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FileInputStream fis = null;
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try {
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fis = SecuritySupport.getFileInputStream(new File(propertiesFilename));
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Properties props = new Properties();
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props.load(fis);
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factoryClassName = props.getProperty(factoryId);
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} catch (Exception x) {
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// assert(x instanceof FileNotFoundException
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// || x instanceof SecurityException)
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// In both cases, ignore and continue w/ next location
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}
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finally {
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// try to close the input stream if one was opened.
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if (fis != null) {
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try {
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fis.close();
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}
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// Ignore the exception.
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catch (IOException exc) {}
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}
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}
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}
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if (factoryClassName != null) {
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if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
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return newInstance(factoryClassName, cl, true);
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}
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// Try Jar Service Provider Mechanism
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Object provider = findJarServiceProvider(factoryId);
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if (provider != null) {
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return provider;
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}
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if (fallbackClassName == null) {
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throw new ConfigurationError(
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"Provider for " + factoryId + " cannot be found", null);
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}
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if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
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return newInstance(fallbackClassName, cl, true);
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} // createObject(String,String,String):Object
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//
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// Private static methods
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//
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/** Returns true if debug has been enabled. */
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private static boolean isDebugEnabled() {
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try {
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String val = SecuritySupport.getSystemProperty("xerces.debug");
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// Allow simply setting the prop to turn on debug
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return (val != null && (!"false".equals(val)));
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}
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catch (SecurityException se) {}
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return false;
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} // isDebugEnabled()
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/** Prints a message to standard error if debugging is enabled. */
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private static void debugPrintln(String msg) {
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if (DEBUG) {
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System.err.println("XERCES: " + msg);
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}
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} // debugPrintln(String)
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/**
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* Figure out which ClassLoader to use. For JDK 1.2 and later use
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* the context ClassLoader.
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*/
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static ClassLoader findClassLoader()
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throws ConfigurationError
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{
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// Figure out which ClassLoader to use for loading the provider
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// class. If there is a Context ClassLoader then use it.
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ClassLoader context = SecuritySupport.getContextClassLoader();
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ClassLoader system = SecuritySupport.getSystemClassLoader();
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ClassLoader chain = system;
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while (true) {
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if (context == chain) {
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// Assert: we are on JDK 1.1 or we have no Context ClassLoader
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// or any Context ClassLoader in chain of system classloader
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// (including extension ClassLoader) so extend to widest
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// ClassLoader (always look in system ClassLoader if Xerces
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// is in boot/extension/system classpath and in current
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// ClassLoader otherwise); normal classloaders delegate
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// back to system ClassLoader first so this widening doesn't
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// change the fact that context ClassLoader will be consulted
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ClassLoader current = ObjectFactory.class.getClassLoader();
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chain = system;
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while (true) {
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if (current == chain) {
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// Assert: Current ClassLoader in chain of
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// boot/extension/system ClassLoaders
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return system;
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}
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if (chain == null) {
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break;
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}
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chain = SecuritySupport.getParentClassLoader(chain);
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}
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// Assert: Current ClassLoader not in chain of
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// boot/extension/system ClassLoaders
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return current;
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}
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if (chain == null) {
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// boot ClassLoader reached
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break;
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}
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// Check for any extension ClassLoaders in chain up to
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// boot ClassLoader
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chain = SecuritySupport.getParentClassLoader(chain);
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};
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// Assert: Context ClassLoader not in chain of
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// boot/extension/system ClassLoaders
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return context;
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} // findClassLoader():ClassLoader
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/**
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* Create an instance of a class using the specified ClassLoader
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*/
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static Object newInstance(String className, ClassLoader cl,
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boolean doFallback)
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throws ConfigurationError
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{
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// assert(className != null);
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try{
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Class providerClass = findProviderClass(className, cl, doFallback);
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Object instance = providerClass.newInstance();
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if (DEBUG) debugPrintln("created new instance of " + providerClass +
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" using ClassLoader: " + cl);
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return instance;
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} catch (ClassNotFoundException x) {
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throw new ConfigurationError(
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"Provider " + className + " not found", x);
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} catch (Exception x) {
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throw new ConfigurationError(
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"Provider " + className + " could not be instantiated: " + x,
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x);
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}
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}
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/**
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* Find a Class using the specified ClassLoader
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*/
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static Class findProviderClass(String className, ClassLoader cl,
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boolean doFallback)
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throws ClassNotFoundException, ConfigurationError
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{
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//throw security exception if the calling thread is not allowed to access the package
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//restrict the access to package as specified in java.security policy
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SecurityManager security = System.getSecurityManager();
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if (security != null) {
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final int lastDot = className.lastIndexOf('.');
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String packageName = className;
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if (lastDot != -1) packageName = className.substring(0, lastDot);
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security.checkPackageAccess(packageName);
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}
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Class providerClass;
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if (cl == null) {
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// XXX Use the bootstrap ClassLoader. There is no way to
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// load a class using the bootstrap ClassLoader that works
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// in both JDK 1.1 and Java 2. However, this should still
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// work b/c the following should be true:
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//
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// (cl == null) iff current ClassLoader == null
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//
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// Thus Class.forName(String) will use the current
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// ClassLoader which will be the bootstrap ClassLoader.
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providerClass = Class.forName(className);
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} else {
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try {
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providerClass = cl.loadClass(className);
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} catch (ClassNotFoundException x) {
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if (doFallback) {
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// Fall back to current classloader
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ClassLoader current = ObjectFactory.class.getClassLoader();
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if (current == null) {
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providerClass = Class.forName(className);
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} else if (cl != current) {
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cl = current;
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providerClass = cl.loadClass(className);
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} else {
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throw x;
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}
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} else {
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throw x;
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}
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}
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}
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return providerClass;
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}
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/*
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* Try to find provider using Jar Service Provider Mechanism
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*
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* @return instance of provider class if found or null
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*/
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private static Object findJarServiceProvider(String factoryId)
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throws ConfigurationError
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{
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String serviceId = "META-INF/services/" + factoryId;
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InputStream is = null;
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// First try the Context ClassLoader
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ClassLoader cl = findClassLoader();
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is = SecuritySupport.getResourceAsStream(cl, serviceId);
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// If no provider found then try the current ClassLoader
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if (is == null) {
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ClassLoader current = ObjectFactory.class.getClassLoader();
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if (cl != current) {
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cl = current;
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is = SecuritySupport.getResourceAsStream(cl, serviceId);
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}
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}
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if (is == null) {
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// No provider found
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return null;
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}
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if (DEBUG) debugPrintln("found jar resource=" + serviceId +
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" using ClassLoader: " + cl);
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// Read the service provider name in UTF-8 as specified in
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// the jar spec. Unfortunately this fails in Microsoft
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// VJ++, which does not implement the UTF-8
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// encoding. Theoretically, we should simply let it fail in
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// that case, since the JVM is obviously broken if it
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// doesn't support such a basic standard. But since there
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// are still some users attempting to use VJ++ for
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// development, we have dropped in a fallback which makes a
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// second attempt using the platform's default encoding. In
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// VJ++ this is apparently ASCII, which is a subset of
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// UTF-8... and since the strings we'll be reading here are
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// also primarily limited to the 7-bit ASCII range (at
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// least, in English versions), this should work well
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// enough to keep us on the air until we're ready to
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// officially decommit from VJ++. [Edited comment from
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// jkesselm]
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BufferedReader rd;
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try {
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rd = new BufferedReader(new InputStreamReader(is, "UTF-8"), DEFAULT_LINE_LENGTH);
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} catch (java.io.UnsupportedEncodingException e) {
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rd = new BufferedReader(new InputStreamReader(is), DEFAULT_LINE_LENGTH);
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}
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String factoryClassName = null;
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try {
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// XXX Does not handle all possible input as specified by the
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// Jar Service Provider specification
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factoryClassName = rd.readLine();
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} catch (IOException x) {
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// No provider found
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return null;
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}
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finally {
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try {
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// try to close the reader.
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rd.close();
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}
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// Ignore the exception.
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catch (IOException exc) {}
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}
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if (factoryClassName != null &&
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! "".equals(factoryClassName)) {
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if (DEBUG) debugPrintln("found in resource, value="
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+ factoryClassName);
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// Note: here we do not want to fall back to the current
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// ClassLoader because we want to avoid the case where the
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// resource file was found using one ClassLoader and the
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// provider class was instantiated using a different one.
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return newInstance(factoryClassName, cl, false);
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}
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// No provider found
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return null;
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}
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//
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// Classes
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//
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/**
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* A configuration error.
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*/
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static final class ConfigurationError
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extends Error {
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/** Serialization version. */
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static final long serialVersionUID = 2646822752226280048L;
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//
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// Data
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//
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/** Exception. */
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private Exception exception;
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//
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// Constructors
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//
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/**
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* Construct a new instance with the specified detail string and
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* exception.
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*/
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ConfigurationError(String msg, Exception x) {
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super(msg);
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this.exception = x;
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} // <init>(String,Exception)
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//
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// methods
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//
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/** Returns the exception associated to this error. */
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Exception getException() {
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return exception;
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} // getException():Exception
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} // class ConfigurationError
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} // class ObjectFactory
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