javax.xml.xpath.XPathFactoryFinder 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: XPathFactoryFinder.java 670432 2008-06-23 02:02:08Z mrglavas $
package javax.xml.xpath;
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.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Properties;
import javax.xml.validation.SchemaFactory;
import libcore.io.IoUtils;
/**
* Implementation of {@link XPathFactory#newInstance(String)}.
*
* @author Kohsuke Kawaguchi
* @version $Revision: 670432 $, $Date: 2008-06-22 19:02:08 -0700 (Sun, 22 Jun 2008) $
* @since 1.5
*/
final class XPathFactoryFinder {
/** debug support code. */
private static boolean debug = false;
/**
* Default columns per line.
*/
private static final int DEFAULT_LINE_LENGTH = 80;
static {
String val = System.getProperty("jaxp.debug");
// Allow simply setting the prop to turn on debug
debug = val != null && (! "false".equals(val));
}
/**
* Cache properties for performance.
*/
private static Properties cacheProps = new Properties();
/**
* First time requires initialization overhead.
*/
private static boolean firstTime = true;
/**
* Conditional debug printing.
*
* @param msg to print
*/
private static void debugPrintln(String msg) {
if (debug) {
System.err.println("JAXP: " + msg);
}
}
/**
* ClassLoader to use to find SchemaFactory.
*/
private final ClassLoader classLoader;
/**
* Constructor that specifies ClassLoader to use
* to find SchemaFactory.
*
* @param loader
* to be used to load resource, {@link SchemaFactory}, and
* {@code SchemaFactoryLoader} implementations during
* the resolution process.
* If this parameter is null, the default system class loader
* will be used.
*/
public XPathFactoryFinder(ClassLoader loader) {
this.classLoader = loader;
if (debug) {
debugDisplayClassLoader();
}
}
private void debugDisplayClassLoader() {
if (classLoader == Thread.currentThread().getContextClassLoader()) {
debugPrintln("using thread context class loader (" + classLoader + ") for search");
return;
}
if (classLoader==ClassLoader.getSystemClassLoader()) {
debugPrintln("using system class loader (" + classLoader + ") for search");
return;
}
debugPrintln("using class loader (" + classLoader + ") for search");
}
/**
* Creates a new {@link XPathFactory} object for the specified
* schema language.
*
* @param uri
* Identifies the underlying object model.
*
* @return null if the callee fails to create one.
*
* @throws NullPointerException
* If the parameter is null.
*/
public XPathFactory newFactory(String uri) {
if (uri == null) {
throw new NullPointerException("uri == null");
}
XPathFactory f = _newFactory(uri);
if (debug) {
if (f != null) {
debugPrintln("factory '" + f.getClass().getName() + "' was found for " + uri);
} else {
debugPrintln("unable to find a factory for " + uri);
}
}
return f;
}
/**
* Lookup a {@link XPathFactory} for the given object model.
*
* @param uri identifies the object model.
*/
private XPathFactory _newFactory(String uri) {
XPathFactory xpf;
String propertyName = SERVICE_CLASS.getName() + ":" + uri;
// system property look up
try {
if (debug) debugPrintln("Looking up system property '"+propertyName+"'" );
String r = System.getProperty(propertyName);
if (r != null && r.length() > 0) {
if (debug) debugPrintln("The value is '"+r+"'");
xpf = createInstance(r);
if(xpf!=null) return xpf;
} else if (debug) {
debugPrintln("The property is undefined.");
}
} catch (Exception e) {
e.printStackTrace();
}
String javah = System.getProperty("java.home");
String configFile = javah + File.separator +
"lib" + File.separator + "jaxp.properties";
String factoryClassName = null ;
// try to read from $java.home/lib/jaxp.properties
try {
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(propertyName);
if (debug) debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");
if (factoryClassName != null) {
xpf = createInstance(factoryClassName);
if(xpf != null){
return xpf;
}
}
} catch (Exception ex) {
if (debug) {
ex.printStackTrace();
}
}
// try META-INF/services files
for (URL resource : createServiceFileIterator()) {
if (debug) debugPrintln("looking into " + resource);
try {
xpf = loadFromServicesFile(uri, resource.toExternalForm(), resource.openStream());
if(xpf!=null) return xpf;
} catch(IOException e) {
if( debug ) {
debugPrintln("failed to read "+resource);
e.printStackTrace();
}
}
}
// platform default
if(uri.equals(XPathFactory.DEFAULT_OBJECT_MODEL_URI)) {
if (debug) debugPrintln("attempting to use the platform default W3C DOM XPath lib");
return createInstance("org.apache.xpath.jaxp.XPathFactoryImpl");
}
if (debug) debugPrintln("all things were tried, but none was found. bailing out.");
return null;
}
/**
* Creates an instance of the specified and returns it.
*
* @param className
* fully qualified class name to be instantiated.
*
* @return null
* if it fails. Error messages will be printed by this method.
*/
XPathFactory createInstance( String className ) {
try {
if (debug) debugPrintln("instantiating "+className);
Class clazz;
if( classLoader!=null )
clazz = classLoader.loadClass(className);
else
clazz = Class.forName(className);
if(debug) debugPrintln("loaded it from "+which(clazz));
Object o = clazz.newInstance();
if( o instanceof XPathFactory )
return (XPathFactory)o;
if (debug) debugPrintln(className+" is not assignable to "+SERVICE_CLASS.getName());
}
// 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) {
if (debug) {
debugPrintln("failed to instantiate "+className);
t.printStackTrace();
}
}
return null;
}
/** Searches for a XPathFactory for a given uri in a META-INF/services file. */
private XPathFactory loadFromServicesFile(String uri, String resourceName, InputStream in) {
if (debug) debugPrintln("Reading " + resourceName );
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(in, "UTF-8"), DEFAULT_LINE_LENGTH);
} catch (java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(in), DEFAULT_LINE_LENGTH);
}
String factoryClassName;
XPathFactory resultFactory = null;
// See spec for provider-configuration files: http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Provider%20Configuration%20File
while (true) {
try {
factoryClassName = rd.readLine();
} catch (IOException x) {
// No provider found
break;
}
if (factoryClassName != null) {
// Ignore comments in the provider-configuration file
int hashIndex = factoryClassName.indexOf('#');
if (hashIndex != -1) {
factoryClassName = factoryClassName.substring(0, hashIndex);
}
// Ignore leading and trailing whitespace
factoryClassName = factoryClassName.trim();
// If there's no text left or if this was a blank line, go to the next one.
if (factoryClassName.length() == 0) {
continue;
}
try {
// Found the right XPathFactory if its isObjectModelSupported(String uri) method returns true.
XPathFactory foundFactory = createInstance(factoryClassName);
if (foundFactory.isObjectModelSupported(uri)) {
resultFactory = foundFactory;
break;
}
} catch (Exception ignored) {
}
}
else {
break;
}
}
IoUtils.closeQuietly(rd);
return resultFactory;
}
/**
* Returns an {@link Iterator} that enumerates all
* the META-INF/services files that we care.
*/
private Iterable createServiceFileIterator() {
if (classLoader == null) {
URL resource = XPathFactoryFinder.class.getClassLoader().getResource(SERVICE_ID);
return Collections.singleton(resource);
} else {
try {
Enumeration e = classLoader.getResources(SERVICE_ID);
if (debug && !e.hasMoreElements()) {
debugPrintln("no "+SERVICE_ID+" file was found");
}
return Collections.list(e);
} catch (IOException e) {
if (debug) {
debugPrintln("failed to enumerate resources "+SERVICE_ID);
e.printStackTrace();
}
return Collections.emptySet();
}
}
}
private static final Class SERVICE_CLASS = XPathFactory.class;
private static final String SERVICE_ID = "META-INF/services/" + SERVICE_CLASS.getName();
private static String which( Class clazz ) {
return which( clazz.getName(), clazz.getClassLoader() );
}
/**
* Search the specified classloader for the given classname.
*
* @param classname the fully qualified name of the class to search for
* @param loader the classloader to search
*
* @return the source location of the resource, or null if it wasn't found
*/
private static String which(String classname, ClassLoader loader) {
String classnameAsResource = classname.replace('.', '/') + ".class";
if (loader==null) loader = ClassLoader.getSystemClassLoader();
URL it = loader.getResource(classnameAsResource);
return it != null ? it.toString() : null;
}
}