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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package javax.xml.xpath;

import com.sun.org.apache.xpath.internal.jaxp.XPathFactoryImpl;
import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Properties;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.function.Supplier;
import jdk.xml.internal.SecuritySupport;

Author:Kohsuke Kawaguchi
Since:1.5
/** * Implementation of {@link XPathFactory#newInstance(String)}. * * @author Kohsuke Kawaguchi * @since 1.5 */
class XPathFactoryFinder { private static final String DEFAULT_PACKAGE = "com.sun.org.apache.xpath.internal";
debug support code.
/** debug support code. */
private static boolean debug = false; static { // Use try/catch block to support applets try { debug = SecuritySupport.getSystemProperty("jaxp.debug") != null; } catch (Exception unused) { debug = false; } }

Cache properties for performance.

/** * <p>Cache properties for performance.</p> */
private static final Properties cacheProps = new Properties();

First time requires initialization overhead.

/** * <p>First time requires initialization overhead.</p> */
private volatile static boolean firstTime = true;

Conditional debug printing.

Params:
  • msgGen – Supplier function that returns debug message
/** * <p>Conditional debug printing.</p> * * @param msgGen Supplier function that returns debug message */
private static void debugPrintln(Supplier<String> msgGen) { if (debug) { System.err.println("JAXP: " + msgGen.get()); } }

ClassLoader to use to find XPathFactory.

/** * <p><code>ClassLoader</code> to use to find <code>XPathFactory</code>.</p> */
private final ClassLoader classLoader;

Constructor that specifies ClassLoader to use to find XPathFactory.

Params:
  • loader – to be used to load resource and XPathFactory implementations during the resolution process. If this parameter is null, the default system class loader will be used.
/** * <p>Constructor that specifies <code>ClassLoader</code> to use * to find <code>XPathFactory</code>.</p> * * @param loader * to be used to load resource and {@link XPathFactory} * 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 == SecuritySupport.getContextClassLoader() ) { debugPrintln(() -> "using thread context class loader ("+classLoader+") for search"); return; } } catch( Throwable unused ) { // 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"); }

Creates a new XPathFactory object for the specified object model.

Params:
  • uri – Identifies the underlying object model.
Throws:
Returns:null if the callee fails to create one.
/** * <p>Creates a new {@link XPathFactory} object for the specified * object model.</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) throws XPathFactoryConfigurationException { 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; }

Lookup a XPathFactory for the given object model.

Params:
  • uri – identifies the object model.
Returns:XPathFactory for the given object model.
/** * <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) throws XPathFactoryConfigurationException { XPathFactory xpathFactory = null; String propertyName = SERVICE_CLASS.getName() + ":" + uri; // system property look up try { debugPrintln(()->"Looking up system property '"+propertyName+"'" ); String r = SecuritySupport.getSystemProperty(propertyName); if(r!=null) { debugPrintln(()->"The value is '"+r+"'"); xpathFactory = createInstance(r); if (xpathFactory != null) { return xpathFactory; } } else debugPrintln(()->"The property is undefined."); } catch( Throwable t ) { if( debug ) { debugPrintln(()->"failed to look up system property '"+propertyName+"'" ); t.printStackTrace(); } } String javah = SecuritySupport.getSystemProperty( "java.home" ); String configFile = javah + File.separator + "conf" + File.separator + "jaxp.properties"; // try to read from $java.home/conf/jaxp.properties try { if(firstTime){ synchronized(cacheProps){ if(firstTime){ File f=new File( configFile ); firstTime = false; if(SecuritySupport.doesFileExist(f)){ debugPrintln(()->"Read properties file " + f); cacheProps.load(SecuritySupport.getFileInputStream(f)); } } } } final String factoryClassName = cacheProps.getProperty(propertyName); debugPrintln(()->"found " + factoryClassName + " in $java.home/conf/jaxp.properties"); if (factoryClassName != null) { xpathFactory = createInstance(factoryClassName); if(xpathFactory != null){ return xpathFactory; } } } catch (Exception ex) { if (debug) { ex.printStackTrace(); } } // Try with ServiceLoader assert xpathFactory == null; xpathFactory = findServiceProvider(uri); // The following assertion should always be true. // Uncomment it, recompile, and run with -ea in case of doubts: // assert xpathFactory == null || xpathFactory.isObjectModelSupported(uri); if (xpathFactory != null) { return xpathFactory; } // platform default if(uri.equals(XPathFactory.DEFAULT_OBJECT_MODEL_URI)) { debugPrintln(()->"attempting to use the platform default W3C DOM XPath lib"); return new XPathFactoryImpl(); } debugPrintln(()->"all things were tried, but none was found. bailing out."); return null; }

Create class using appropriate ClassLoader.

Params:
  • className – Name of class to create.
Returns:Created class or null.
/** <p>Create class using appropriate ClassLoader.</p> * * @param className Name of class to create. * @return Created class or <code>null</code>. */
private Class<?> createClass(String className) { Class<?> clazz; // make sure we have access to restricted packages boolean internal = false; if (System.getSecurityManager() != null) { if (className != null && className.startsWith(DEFAULT_PACKAGE)) { internal = true; } } // use approprite ClassLoader try { if (classLoader != null && !internal) { clazz = Class.forName(className, false, classLoader); } else { clazz = Class.forName(className); } } catch (Throwable t) { if(debug) { t.printStackTrace(); } return null; } return clazz; }

Creates an instance of the specified and returns it.

Params:
  • className – fully qualified class name to be instantiated.
Returns:null if it fails. Error messages will be printed by this method.
/** * <p>Creates an instance of the specified and returns it.</p> * * @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) throws XPathFactoryConfigurationException { XPathFactory xPathFactory = null; debugPrintln(()->"createInstance(" + className + ")"); // get Class from className Class<?> clazz = createClass(className); if (clazz == null) { debugPrintln(()->"failed to getClass(" + className + ")"); return null; } debugPrintln(()->"loaded " + className + " from " + which(clazz)); // instantiate Class as a XPathFactory try { xPathFactory = (XPathFactory) clazz.getConstructor().newInstance(); } catch (ClassCastException | IllegalAccessException | IllegalArgumentException | InstantiationException | InvocationTargetException | NoSuchMethodException | SecurityException ex) { debugPrintln(()->"could not instantiate " + clazz.getName()); if (debug) { ex.printStackTrace(); } return null; } return xPathFactory; } // Call isObjectModelSupportedBy with initial context. private boolean isObjectModelSupportedBy(final XPathFactory factory, final String objectModel, AccessControlContext acc) { return AccessController.doPrivileged(new PrivilegedAction<Boolean>() { public Boolean run() { return factory.isObjectModelSupported(objectModel); } }, acc); }
Finds a service provider subclass of XPathFactory that supports the given object model using the ServiceLoader.
Params:
  • objectModel – URI of object model to support.
Throws:
Returns:An XPathFactory supporting the specified object model, or null if none is found.
/** * Finds a service provider subclass of XPathFactory that supports the * given object model using the ServiceLoader. * * @param objectModel URI of object model to support. * @return An XPathFactory supporting the specified object model, or null * if none is found. * @throws XPathFactoryConfigurationException if a configuration error is found. */
private XPathFactory findServiceProvider(final String objectModel) throws XPathFactoryConfigurationException { assert objectModel != null; // store current context. final AccessControlContext acc = AccessController.getContext(); try { return AccessController.doPrivileged(new PrivilegedAction<XPathFactory>() { public XPathFactory run() { final ServiceLoader<XPathFactory> loader = ServiceLoader.load(SERVICE_CLASS); for (XPathFactory factory : loader) { // restore initial context to call // factory.isObjectModelSupportedBy if (isObjectModelSupportedBy(factory, objectModel, acc)) { return factory; } } return null; // no factory found. } }); } catch (ServiceConfigurationError error) { throw new XPathFactoryConfigurationException(error); } } private static final Class<XPathFactory> SERVICE_CLASS = XPathFactory.class; // Used for debugging purposes private static String which( Class<?> clazz ) { return SecuritySupport.getClassSource(clazz); } }