javax.xml.stream.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 670281 2008-06-22 00:55:09Z mrglavas $
package javax.xml.stream;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;
/**
* This class is duplicated for each JAXP subpackage so keep it in
* sync. It is package private.
*
* 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 including
* JVMs that perform early linking like the Microsoft JVM in IE 5. Note
* however that it must be compiled on a JDK version 1.2 or later system
* since it calls Thread#getContextClassLoader(). The code also runs both
* as part of an unbundled jar file and when bundled as part of the JDK.
*/
final class 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;
// Define system property "jaxp.debug" to get output
static {
// Use try/catch block to support applets, which throws
// SecurityException out of this code.
try {
String val = SecuritySupport.getSystemProperty("jaxp.debug");
// Allow simply setting the prop to turn on debug
debug = val != null && (! "false".equals(val));
} catch (SecurityException se) {
debug = false;
}
}
private FactoryFinder() {}
private static void dPrint(String msg) {
if (debug) {
System.err.println("JAXP: " + msg);
}
}
/**
* Create an instance of a class using the specified ClassLoader and
* optionally fall back to the current ClassLoader if not found.
*
* @param className Name of the concrete class corresponding to the
* service provider
*
* @param cl ClassLoader to use to load the class, null means to use
* the bootstrap ClassLoader
*
* @param doFallback true if the current ClassLoader should be tried as
* a fallback if the class is not found using cl
*/
private static Object newInstance(String className, ClassLoader cl,
boolean doFallback)
throws ConfigurationError
{
// assert(className != null);
try {
Class providerClass;
if (cl == null) {
// If classloader is null Use the bootstrap ClassLoader.
// Thus Class.forName(String) will use the current
// ClassLoader which will be the bootstrap ClassLoader.
providerClass = Class.forName(className);
} else {
try {
providerClass = cl.loadClass(className);
} catch (ClassNotFoundException x) {
if (doFallback) {
// Fall back to current classloader
cl = FactoryFinder.class.getClassLoader();
if (cl != null) {
providerClass = cl.loadClass(className);
}
else {
providerClass = Class.forName(className);
}
} else {
throw x;
}
}
}
Object instance = providerClass.newInstance();
if (debug) dPrint("created new instance of " + providerClass +
" using ClassLoader: " + cl);
return instance;
} 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.
* @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.
*
* Package private so this code can be shared.
*/
static Object find(String factoryId, String fallbackClassName)
throws ConfigurationError {
// Figure out which ClassLoader to use for loading the provider
// class. If there is a Context ClassLoader then use it.
ClassLoader classLoader = SecuritySupport.getContextClassLoader();
if (classLoader == null) {
// if we have no Context ClassLoader
// so use the current ClassLoader
classLoader = FactoryFinder.class.getClassLoader();
}
return find(factoryId, classLoader, fallbackClassName);
}
/**
* Finds the implementation Class object in the specified order. Main
* entry point.
* @return Class object of factory, never null
*
* @param factoryId Name of the factory to find, same as
* a property name
* @param classLoader The ClassLoader to use
* @param fallbackClassName Implementation class name, if nothing else
* is found. Use null to mean no fallback.
*
* Package private so this code can be shared.
*/
static Object find(String factoryId, ClassLoader classLoader, String fallbackClassName)
throws ConfigurationError {
if (debug) dPrint("find factoryId =" + factoryId);
// Use the system property first
try {
String systemProp = SecuritySupport.getSystemProperty(factoryId);
if (systemProp != null && systemProp.length() > 0) {
if (debug) dPrint("found system property, value=" + systemProp);
return newInstance(systemProp, classLoader, true);
}
} catch (SecurityException se) {
//if first option fails due to any reason we should try next option in the
//look up algorithm.
}
// try to read from $java.home/lib/stax.properties
try {
String javah = SecuritySupport.getSystemProperty("java.home");
String configFile = javah + File.separator +
"lib" + File.separator + "stax.properties";
String factoryClassName = null;
if(firstTime){
synchronized(cacheProps){
if(firstTime){
File f=new File( configFile );
firstTime = false;
if(SecuritySupport.doesFileExist(f)){
if (debug) dPrint("Read properties file "+f);
//cacheProps.load( new FileInputStream(f));
cacheProps.load(SecuritySupport.getFileInputStream(f));
}
}
}
}
factoryClassName = cacheProps.getProperty(factoryId);
if(factoryClassName != null){
if (debug) dPrint("found in $java.home/stax.properties, value=" + factoryClassName);
return newInstance(factoryClassName, classLoader, true);
}
} 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) dPrint("loaded from fallback value: " + fallbackClassName);
return newInstance(fallbackClassName, classLoader, true);
}
/*
* 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 = SecuritySupport.getContextClassLoader();
if (cl != null) {
is = SecuritySupport.getResourceAsStream(cl, serviceId);
// If no provider found then try the current ClassLoader
if (is == null) {
cl = FactoryFinder.class.getClassLoader();
is = SecuritySupport.getResourceAsStream(cl, serviceId);
}
} else {
// No Context ClassLoader, try the current
// ClassLoader
cl = FactoryFinder.class.getClassLoader();
is = SecuritySupport.getResourceAsStream(cl, serviceId);
}
if (is == null) {
// No provider found
return null;
}
if (debug) dPrint("found jar resource=" + serviceId +
" using ClassLoader: " + cl);
// 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(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 {
try {
// try to close the reader.
rd.close();
}
// Ignore the exception.
catch (IOException exc) {}
}
if (factoryClassName != null &&
! "".equals(factoryClassName)) {
if (debug) dPrint("found in resource, value="
+ factoryClassName);
// Note: here we do not want to fall back to the current
// ClassLoader because we want to avoid the case where the
// resource file was found using one ClassLoader and the
// provider class was instantiated using a different one.
return newInstance(factoryClassName, cl, false);
}
// No provider found
return null;
}
static class ConfigurationError extends Error {
private static final long serialVersionUID = 1L;
private Exception exception;
/**
* Construct a new instance with the specified detail string and
* exception.
*/
ConfigurationError(String msg, Exception x) {
super(msg);
this.exception = x;
}
Exception getException() {
return exception;
}
}
}