Java tutorial
/* * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.xml.xpath; import com.sun.org.apache.xpath.internal.jaxp.XPathFactoryImpl; import jdk.xml.internal.SecuritySupport; /** * <p>An {@code XPathFactory} instance can be used to create * {@link javax.xml.xpath.XPath} objects.</p> * *<p>See {@link #newInstance(String uri)} for lookup mechanism.</p> * * <p>The {@link XPathFactory} class is not thread-safe. In other words, * it is the application's responsibility to ensure that at most * one thread is using a {@link XPathFactory} object at any * given moment. Implementations are encouraged to mark methods * as <code>synchronized</code> to protect themselves from broken clients. * * <p>{@link XPathFactory} is not re-entrant. While one of the * <code>newInstance</code> methods is being invoked, applications * may not attempt to recursively invoke a <code>newInstance</code> method, * even from the same thread. * * @author Norman Walsh * @author Jeff Suttor * * @since 1.5 */ public abstract class XPathFactory { /** * <p>The default property name according to the JAXP spec.</p> */ public static final String DEFAULT_PROPERTY_NAME = "javax.xml.xpath.XPathFactory"; /** * <p>Default Object Model URI.</p> */ public static final String DEFAULT_OBJECT_MODEL_URI = "http://java.sun.com/jaxp/xpath/dom"; /** * <p>Protected constructor as {@link #newInstance()} or {@link #newInstance(String uri)} * or {@link #newInstance(String uri, String factoryClassName, ClassLoader classLoader)} * should be used to create a new instance of an {@code XPathFactory}.</p> */ protected XPathFactory() { } /** * Creates a new instance of the {@code XPathFactory} builtin * system-default implementation. * * @implSpec The {@code XPathFactory} builtin * system-default implementation is only required to support the * {@link #DEFAULT_OBJECT_MODEL_URI default object model}, the * {@linkplain org.w3c.dom W3C DOM}, but may support additional * object models. * * @return A new instance of the {@code XPathFactory} builtin * system-default implementation. * * @since 9 */ public static XPathFactory newDefaultInstance() { return new XPathFactoryImpl(); } /** * <p>Get a new {@code XPathFactory} instance using the default object model, * {@link #DEFAULT_OBJECT_MODEL_URI}, * the W3C DOM.</p> * * <p>This method is functionally equivalent to:</p> * <pre> * newInstance(DEFAULT_OBJECT_MODEL_URI) * </pre> * * <p>Since the implementation for the W3C DOM is always available, this method will never fail.</p> * * @return Instance of an {@code XPathFactory}. * * @throws RuntimeException When there is a failure in creating an * {@code XPathFactory} for the default object model. */ public static XPathFactory newInstance() { try { return newInstance(DEFAULT_OBJECT_MODEL_URI); } catch (XPathFactoryConfigurationException e) { throw new RuntimeException( "XPathFactory#newInstance() failed to create an XPathFactory for the default object model: " + DEFAULT_OBJECT_MODEL_URI + " with the XPathFactoryConfigurationException: " + e.getMessage(), e); } } /** * <p>Get a new {@code XPathFactory} instance using the specified object model.</p> * * <p>To find a {@code XPathFactory} object, * this method looks the following places in the following order where "the class loader" refers to the context class loader:</p> * <ol> * <li> * <p> * If the system property {@link #DEFAULT_PROPERTY_NAME} + ":uri" is present, * where uri is the parameter to this method, then its value is read as a class name. * The method will try to create a new instance of this class by using the class loader, * and returns it if it is successfully created. * </li> * <li> * <p> * Use the configuration file "jaxp.properties". The file is in standard * {@link java.util.Properties} format and typically located in the * conf directory of the Java installation. It contains the fully qualified * name of the implementation class with the key being the system property * defined above. * <p> * The jaxp.properties file is read only once by the JAXP implementation * and its values are then cached for future use. If the file does not exist * when the first attempt is made to read from it, no further attempts are * made to check for its existence. It is not possible to change the value * of any property in jaxp.properties after it has been read for the first time. * </li> * <li> * <p> * Use the service-provider loading facility, defined by the * {@link java.util.ServiceLoader} class, to attempt to locate and load an * implementation of the service using the {@linkplain * java.util.ServiceLoader#load(java.lang.Class) default loading mechanism}: * the service-provider loading facility will use the {@linkplain * java.lang.Thread#getContextClassLoader() current thread's context class loader} * to attempt to load the service. If the context class * loader is null, the {@linkplain * ClassLoader#getSystemClassLoader() system class loader} will be used. * <br> * Each potential service provider is required to implement the method * {@link #isObjectModelSupported(String objectModel)}. * The first service provider found that supports the specified object * model is returned. * <br> * In case of {@link java.util.ServiceConfigurationError} an * {@link XPathFactoryConfigurationException} will be thrown. * </li> * <li> * <p> * Platform default {@code XPathFactory} is located in a platform * specific way. * There must be a {@linkplain #newDefaultInstance() platform default} * {@code XPathFactory} for the W3C DOM, i.e. * {@link #DEFAULT_OBJECT_MODEL_URI}. * </li> * </ol> * <p>If everything fails, an {@code XPathFactoryConfigurationException} will be thrown. * * <p>Tip for Trouble-shooting: * <p>See {@link java.util.Properties#load(java.io.InputStream)} for exactly how a property file is parsed. * In particular, colons ':' need to be escaped in a property file, so make sure the URIs are properly escaped in it. * For example: * <pre> * http\://java.sun.com/jaxp/xpath/dom=org.acme.DomXPathFactory * </pre> * * @param uri Identifies the underlying object model. * The specification only defines the URI {@link #DEFAULT_OBJECT_MODEL_URI}, * <code>http://java.sun.com/jaxp/xpath/dom</code> for the W3C DOM, * the org.w3c.dom package, and implementations are free to introduce other URIs for other object models. * * @return Instance of an {@code XPathFactory}. * * @throws XPathFactoryConfigurationException If the specified object model * is unavailable, or if there is a configuration error. * @throws NullPointerException If <code>uri</code> is <code>null</code>. * @throws IllegalArgumentException If <code>uri</code> is <code>null</code> * or <code>uri.length() == 0</code>. */ public static XPathFactory newInstance(final String uri) throws XPathFactoryConfigurationException { if (uri == null) { throw new NullPointerException( "XPathFactory#newInstance(String uri) cannot be called with uri == null"); } if (uri.length() == 0) { throw new IllegalArgumentException( "XPathFactory#newInstance(String uri) cannot be called with uri == \"\""); } ClassLoader classLoader = SecuritySupport.getContextClassLoader(); if (classLoader == null) { //use the current class loader classLoader = XPathFactory.class.getClassLoader(); } XPathFactory xpathFactory = new XPathFactoryFinder(classLoader).newFactory(uri); if (xpathFactory == null) { throw new XPathFactoryConfigurationException( "No XPathFactory implementation found for the object model: " + uri); } return xpathFactory; } /** * <p>Obtain a new instance of a {@code XPathFactory} from a factory class name. {@code XPathFactory} * is returned if specified factory class supports the specified object model. * This function is useful when there are multiple providers in the classpath. * It gives more control to the application as it can specify which provider * should be loaded.</p> * * * <h4>Tip for Trouble-shooting</h4> * <p>Setting the <code>jaxp.debug</code> system property will cause * this method to print a lot of debug messages * to <code>System.err</code> about what it is doing and where it is looking at.</p> * * <p> If you have problems try:</p> * <pre> * java -Djaxp.debug=1 YourProgram .... * </pre> * * @param uri Identifies the underlying object model. The specification only defines the URI * {@link #DEFAULT_OBJECT_MODEL_URI},<code>http://java.sun.com/jaxp/xpath/dom</code> * for the W3C DOM, the org.w3c.dom package, and implementations are free to introduce * other URIs for other object models. * * @param factoryClassName fully qualified factory class name that provides implementation of <code>javax.xml.xpath.XPathFactory</code>. * * @param classLoader <code>ClassLoader</code> used to load the factory class. If <code>null</code> * current <code>Thread</code>'s context classLoader is used to load the factory class. * * * @return New instance of a {@code XPathFactory} * * @throws XPathFactoryConfigurationException * if <code>factoryClassName</code> is <code>null</code>, or * the factory class cannot be loaded, instantiated * or the factory class does not support the object model specified * in the <code>uri</code> parameter. * * @throws NullPointerException If <code>uri</code> is <code>null</code>. * @throws IllegalArgumentException If <code>uri</code> is <code>null</code> * or <code>uri.length() == 0</code>. * * @see #newInstance() * @see #newInstance(String uri) * * @since 1.6 */ public static XPathFactory newInstance(String uri, String factoryClassName, ClassLoader classLoader) throws XPathFactoryConfigurationException { ClassLoader cl = classLoader; if (uri == null) { throw new NullPointerException( "XPathFactory#newInstance(String uri) cannot be called with uri == null"); } if (uri.length() == 0) { throw new IllegalArgumentException( "XPathFactory#newInstance(String uri) cannot be called with uri == \"\""); } if (cl == null) { cl = SecuritySupport.getContextClassLoader(); } XPathFactory f = new XPathFactoryFinder(cl).createInstance(factoryClassName); if (f == null) { throw new XPathFactoryConfigurationException( "No XPathFactory implementation found for the object model: " + uri); } //if this factory supports the given schemalanguage return this factory else thrown exception if (f.isObjectModelSupported(uri)) { return f; } else { throw new XPathFactoryConfigurationException( "Factory " + factoryClassName + " doesn't support given " + uri + " object model"); } } /** * <p>Is specified object model supported by this {@code XPathFactory}?</p> * * @param objectModel Specifies the object model which the returned {@code XPathFactory} will understand. * * @return <code>true</code> if {@code XPathFactory} supports <code>objectModel</code>, else <code>false</code>. * * @throws NullPointerException If <code>objectModel</code> is <code>null</code>. * @throws IllegalArgumentException If <code>objectModel.length() == 0</code>. */ public abstract boolean isObjectModelSupported(String objectModel); /** * <p>Set a feature for this {@code XPathFactory} and * <code>XPath</code>s created by this factory.</p> * * <p> * Feature names are fully qualified {@link java.net.URI}s. * Implementations may define their own features. * An {@link XPathFactoryConfigurationException} is thrown if this * {@code XPathFactory} or the <code>XPath</code>s * it creates cannot support the feature. * It is possible for an {@code XPathFactory} to expose a feature value * but be unable to change its state. * </p> * * <p> * All implementations are required to support the {@link javax.xml.XMLConstants#FEATURE_SECURE_PROCESSING} feature. * When the feature is <code>true</code>, any reference to an external function is an error. * Under these conditions, the implementation must not call the {@link XPathFunctionResolver} * and must throw an {@link XPathFunctionException}. * </p> * * @param name Feature name. * @param value Is feature state <code>true</code> or <code>false</code>. * * @throws XPathFactoryConfigurationException if this {@code XPathFactory} or the <code>XPath</code>s * it creates cannot support this feature. * @throws NullPointerException if <code>name</code> is <code>null</code>. */ public abstract void setFeature(String name, boolean value) throws XPathFactoryConfigurationException; /** * <p>Get the state of the named feature.</p> * * <p> * Feature names are fully qualified {@link java.net.URI}s. * Implementations may define their own features. * An {@link XPathFactoryConfigurationException} is thrown if this * {@code XPathFactory} or the <code>XPath</code>s * it creates cannot support the feature. * It is possible for an {@code XPathFactory} to expose a feature value * but be unable to change its state. * </p> * * @param name Feature name. * * @return State of the named feature. * * @throws XPathFactoryConfigurationException if this * {@code XPathFactory} or the <code>XPath</code>s * it creates cannot support this feature. * @throws NullPointerException if <code>name</code> is <code>null</code>. */ public abstract boolean getFeature(String name) throws XPathFactoryConfigurationException; /** * <p>Establish a default variable resolver.</p> * * <p>Any <code>XPath</code> objects constructed from this factory will use * the specified resolver by default.</p> * * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> * is <code>null</code>.</p> * * @param resolver Variable resolver. * * @throws NullPointerException If <code>resolver</code> is * <code>null</code>. */ public abstract void setXPathVariableResolver(XPathVariableResolver resolver); /** * <p>Establish a default function resolver.</p> * * <p>Any <code>XPath</code> objects constructed from this factory will * use the specified resolver by default.</p> * * <p>A <code>NullPointerException</code> is thrown if * <code>resolver</code> is <code>null</code>.</p> * * @param resolver XPath function resolver. * * @throws NullPointerException If <code>resolver</code> is * <code>null</code>. */ public abstract void setXPathFunctionResolver(XPathFunctionResolver resolver); /** * <p>Return a new <code>XPath</code> using the underlying object * model determined when the {@code XPathFactory} was instantiated.</p> * * @return New instance of an <code>XPath</code>. */ public abstract XPath newXPath(); }