// $Id: XPathFactoryFinder.java,v 1.2.8.1.2.1 2004/09/16 09:25:16 nb131165 Exp $
/*
* @(#)XPathFactoryFinder.java 1.5 05/01/04
*
* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package javax.xml.xpath;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Properties;
/**
* Implementation of {@link XPathFactory#newInstance(String)}.
*
* @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
* @version $Revision: 1.2.8.1.2.1 $, $Date: 2004/09/16 09:25:16 $
* @since 1.5
*/
class XPathFactoryFinder {
private static SecuritySupport ss = new SecuritySupport() ;
/** debug support code. */
private static boolean debug = false;
static {
// Use try/catch block to support applets
try {
debug = ss.getSystemProperty("jaxp.debug") != null;
} catch (Exception _) {
debug = false;
}
}
/**
* <p>Cache properties for performance.</p>
*/
private static Properties cacheProps = new Properties();
/**
* <p>First time requires initialization overhead.</p>
*/
private static boolean firstTime = true;
/**
* <p>Conditional debug printing.</p>
*
* @param msg to print
*/
private static void debugPrintln(String msg) {
if (debug) {
System.err.println("JAXP: " + msg);
}
}
/**
* <p><code>ClassLoader</code> to use to find <code>SchemaFactory</code>.</p>
*/
private final ClassLoader classLoader;
/**
* <p>Constructor that specifies <code>ClassLoader</code> to use
* to find <code>SchemaFactory</code>.</p>
*
* @param loader
* to be used to load resource, {@link SchemaFactory}, and
* {@link 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() {
try {
if( classLoader == ss.getContextClassLoader() ) {
debugPrintln("using thread context class loader ("+classLoader+") for search");
return;
}
} catch( Throwable _ ) {
; // getContextClassLoader() undefined in JDK1.1
}
if( classLoader==ClassLoader.getSystemClassLoader() ) {
debugPrintln("using system class loader ("+classLoader+") for search");
return;
}
debugPrintln("using class loader ("+classLoader+") for search");
}
/**
* <p>Creates a new {@link XPathFactory} object for the specified
* schema language.</p>
*
* @param uri
* Identifies the underlying object model.
*
* @return <code>null</code> 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();
XPathFactory f = _newFactory(uri);
if (f != null) {
debugPrintln("factory '" + f.getClass().getName() + "' was found for " + uri);
} else {
debugPrintln("unable to find a factory for " + uri);
}
return f;
}
/**
* <p>Lookup a {@link XPathFactory} for the given object model.</p>
*
* @param uri identifies the object model.
*
* @return {@link XPathFactory} for the given object model.
*/
private XPathFactory _newFactory(String uri) {
XPathFactory sf;
String propertyName = SERVICE_CLASS.getName() + ":" + uri;
// system property look up
try {
debugPrintln("Looking up system property '"+propertyName+"'" );
String r = ss.getSystemProperty(propertyName);
if(r!=null) {
debugPrintln("The value is '"+r+"'");
sf = createInstance(r);
if(sf!=null) return sf;
} else
debugPrintln("The property is undefined.");
} catch( Throwable t ) {
if( debug ) {
debugPrintln("failed to look up system property '"+propertyName+"'" );
t.printStackTrace();
}
}
String javah = ss.getSystemProperty( "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(ss.doesFileExist(f)){
debugPrintln("Read properties file " + f);
cacheProps.load(ss.getFileInputStream(f));
}
}
}
}
factoryClassName = cacheProps.getProperty(propertyName);
debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");
if (factoryClassName != null) {
sf = createInstance(factoryClassName);
if(sf != null){
return sf;
}
}
} catch (Exception ex) {
if (debug) {
ex.printStackTrace();
}
}
// try META-INF/services files
Iterator sitr = createServiceFileIterator();
while(sitr.hasNext()) {
URL resource = (URL)sitr.next();
debugPrintln("looking into " + resource);
try {
//sf = loadFromProperty(uri,resource.toExternalForm(),resource.openStream());
sf = loadFromProperty(uri,resource.toExternalForm(),ss.getURLInputStream(resource));
if(sf!=null) return sf;
} catch(IOException e) {
if( debug ) {
debugPrintln("failed to read "+resource);
e.printStackTrace();
}
}
}
// platform default
if(uri.equals(XPathFactory.DEFAULT_OBJECT_MODEL_URI)) {
debugPrintln("attempting to use the platform default W3C DOM XPath lib");
return createInstance("com.sun.org.apache.xpath.internal.jaxp.XPathFactoryImpl");
}
debugPrintln("all things were tried, but none was found. bailing out.");
return null;
}
/**
* <p>Creates an instance of the specified and returns it.</p>
*
* @param className
* fully qualified class name to be instanciated.
*
* @return null
* if it fails. Error messages will be printed by this method.
*/
private XPathFactory createInstance( String className ) {
try {
debugPrintln("instanciating "+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;
debugPrintln(className+" is not assignable to "+SERVICE_CLASS.getName());
} catch( Throwable t ) {
debugPrintln("failed to instanciate "+className);
if(debug) t.printStackTrace();
}
return null;
}
/** Iterator that lazily computes one value and returns it. */
private static abstract class SingleIterator implements Iterator {
private boolean seen = false;
public final void remove() { throw new UnsupportedOperationException(); }
public final boolean hasNext() { return !seen; }
public final Object next() {
if(seen) throw new NoSuchElementException();
seen = true;
return value();
}
protected abstract Object value();
}
/**
* Looks up a value in a property file
* while producing all sorts of debug messages.
*
* @return null
* if there was an error.
*/
private XPathFactory loadFromProperty( String keyName, String resourceName, InputStream in )
throws IOException {
debugPrintln("Reading "+resourceName );
Properties props = new Properties();
props.load(in);
in.close();
String factoryClassName = props.getProperty(keyName);
if(factoryClassName != null){
debugPrintln("found "+keyName+" = " + factoryClassName);
return createInstance(factoryClassName);
} else {
debugPrintln(keyName+" is not in the property file");
return null;
}
}
/**
* Returns an {@link Iterator} that enumerates all
* the META-INF/services files that we care.
*/
private Iterator createServiceFileIterator() {
if (classLoader == null) {
return new SingleIterator() {
protected Object value() {
ClassLoader classLoader = XPathFactoryFinder.class.getClassLoader();
return ss.getResourceAsURL(classLoader, SERVICE_ID);
//return (ClassLoader.getSystemResource( SERVICE_ID ));
}
};
} else {
try {
//final Enumeration e = classLoader.getResources(SERVICE_ID);
final Enumeration e = ss.getResources(classLoader, SERVICE_ID);
if(!e.hasMoreElements()) {
debugPrintln("no "+SERVICE_ID+" file was found");
}
// wrap it into an Iterator.
return new Iterator() {
public void remove() {
throw new UnsupportedOperationException();
}
public boolean hasNext() {
return e.hasMoreElements();
}
public Object next() {
return e.nextElement();
}
};
} catch (IOException e) {
debugPrintln("failed to enumerate resources "+SERVICE_ID);
if(debug) e.printStackTrace();
return new ArrayList().iterator(); // empty iterator
}
}
}
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() );
}
/**
* <p>Search the specified classloader for the given classname.</p>
*
* @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);
URL it = ss.getResourceAsURL(loader, classnameAsResource);
if (it != null) {
return it.toString();
} else {
return null;
}
}
}
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