javax.xml.datatype.FactoryFinder Maven / Gradle / Ivy
/*
* 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: FactoryFinder.java 670432 2008-06-23 02:02:08Z mrglavas $
package javax.xml.datatype;
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.Properties;
import libcore.io.IoUtils;
/**
* Implement pluggable data types.
*
* This class is duplicated for each JAXP subpackage so keep it in
* sync. It is package private for secure class loading.
*
* @author Jeff Suttor
* @version $Revision: 670432 $, $Date: 2008-06-22 19:02:08 -0700 (Sun, 22 Jun 2008) $
* @since 1.5
*/
final class FactoryFinder {
/** Name of class to display in output messages.
*/
private static final String CLASS_NAME = "javax.xml.datatype.FactoryFinder";
/** Debug flag to trace loading process.
*/
private static boolean debug = false;
/** Cache properties for performance.
*/
private static Properties cacheProps = new Properties();
/** First time requires initialization overhead.
*/
private static boolean firstTime = true;
/** Default columns per line. */
private static final int DEFAULT_LINE_LENGTH = 80;
/**
* Check to see if debugging enabled by property.
*
* Use try/catch block to support applets, which throws
* SecurityException out of this code.
*/
static {
String val = System.getProperty("jaxp.debug");
// Allow simply setting the prop to turn on debug
debug = val != null && (! "false".equals(val));
}
private FactoryFinder() {}
/**
* Output debugging messages.
*
* @param msg String to print to stderr.
*/
private static void debugPrintln(String msg) {
if (debug) {
System.err.println(
CLASS_NAME
+ ":"
+ msg);
}
}
/**
* Find the appropriate ClassLoader to use.
*
* The context ClassLoader is preferred.
*
* @return ClassLoader to use.
*
* @throws ConfigurationError If a valid ClassLoader cannot be identified.
*/
private static ClassLoader findClassLoader() throws ConfigurationError {
// Figure out which ClassLoader to use for loading the provider
// class. If there is a Context ClassLoader then use it.
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
if (debug) debugPrintln(
"Using context class loader: "
+ classLoader);
if (classLoader == null) {
// if we have no Context ClassLoader
// so use the current ClassLoader
classLoader = FactoryFinder.class.getClassLoader();
if (debug) debugPrintln(
"Using the class loader of FactoryFinder: "
+ classLoader);
}
return classLoader;
}
/**
* Create an instance of a class using the specified ClassLoader.
*
* @param className Name of class to create.
* @param classLoader ClassLoader to use to create named class.
*
* @return New instance of specified class created using the specified ClassLoader.
*
* @throws ConfigurationError If class could not be created.
*/
static Object newInstance(
String className,
ClassLoader classLoader)
throws ConfigurationError {
try {
Class spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
spiClass = classLoader.loadClass(className);
}
if (debug) {
debugPrintln("Loaded " + className + " from " + which(spiClass));
}
return spiClass.newInstance();
} catch (ClassNotFoundException x) {
throw new ConfigurationError(
"Provider " + className + " not found", x);
} catch (Exception x) {
throw new ConfigurationError(
"Provider " + className + " could not be instantiated: " + x, x);
}
}
/**
* Finds the implementation Class object in the specified order. Main
* entry point.
* Package private so this code can be shared.
*
* @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.
*
* @return Class Object of factory, never null
*
* @throws ConfigurationError If Class cannot be found.
*/
static Object find(String factoryId, String fallbackClassName) throws ConfigurationError {
ClassLoader classLoader = findClassLoader();
// Use the system property first
String systemProp = System.getProperty(factoryId);
if (systemProp != null && systemProp.length() > 0) {
if (debug) debugPrintln("found " + systemProp + " in the system property " + factoryId);
return newInstance(systemProp, classLoader);
}
// try to read from $java.home/lib/jaxp.properties
try {
String javah = System.getProperty("java.home");
String configFile = javah + File.separator + "lib" + File.separator + "jaxp.properties";
String factoryClassName = null;
if (firstTime) {
synchronized (cacheProps) {
if (firstTime) {
File f = new File(configFile);
firstTime = false;
if (f.exists()) {
if (debug) debugPrintln("Read properties file " + f);
cacheProps.load(new FileInputStream(f));
}
}
}
}
factoryClassName = cacheProps.getProperty(factoryId);
if (debug) debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");
if (factoryClassName != null) {
return newInstance(factoryClassName, classLoader);
}
} catch (Exception ex) {
if (debug) {
ex.printStackTrace();
}
}
// 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("loaded from fallback value: " + fallbackClassName);
return newInstance(fallbackClassName, classLoader);
}
/*
* Try to find provider using Jar Service Provider Mechanism
*
* @return instance of provider class if found or null
*/
private static Object findJarServiceProvider(String factoryId) throws ConfigurationError {
String serviceId = "META-INF/services/" + factoryId;
InputStream is = null;
// First try the Context ClassLoader
ClassLoader cl = Thread.currentThread().getContextClassLoader();
if (cl != null) {
is = cl.getResourceAsStream(serviceId);
}
if (is == null) {
cl = FactoryFinder.class.getClassLoader();
is = cl.getResourceAsStream(serviceId);
}
if (is == null) {
// No provider found
return null;
}
if (debug) debugPrintln("found jar resource=" + serviceId + " using ClassLoader: " + cl);
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(is, "UTF-8"), DEFAULT_LINE_LENGTH);
} catch (java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(is), DEFAULT_LINE_LENGTH);
}
String factoryClassName = null;
try {
// XXX Does not handle all possible input as specified by the
// Jar Service Provider specification
factoryClassName = rd.readLine();
} catch (IOException x) {
// No provider found
return null;
} finally {
IoUtils.closeQuietly(rd);
}
if (factoryClassName != null &&
! "".equals(factoryClassName)) {
if (debug) debugPrintln("found in resource, value="
+ factoryClassName);
return newInstance(factoryClassName, cl);
}
// No provider found
return null;
}
/**
* Configuration Error.
*/
static class ConfigurationError extends Error {
private static final long serialVersionUID = -3644413026244211347L;
/**
* Exception that caused the error.
*/
private Exception exception;
/**
* Construct a new instance with the specified detail string and
* exception.
*
* @param msg Detail message for this error.
* @param x Exception that caused the error.
*/
ConfigurationError(String msg, Exception x) {
super(msg);
this.exception = x;
}
/**
* Get the Exception that caused the error.
*
* @return Exception that caused the error.
*/
Exception getException() {
return exception;
}
}
/**
* Returns the location where the given Class is loaded from.
*/
private static String which(Class clazz) {
try {
String classnameAsResource = clazz.getName().replace('.', '/') + ".class";
ClassLoader loader = clazz.getClassLoader();
URL it;
if (loader != null) {
it = loader.getResource(classnameAsResource);
} else {
it = ClassLoader.getSystemResource(classnameAsResource);
}
if (it != null) {
return it.toString();
}
}
// 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) {
// work defensively.
if (debug) {
t.printStackTrace();
}
}
return "unknown location";
}
}