Java tutorial
/* * Copyright (c) 2010, 2013, 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.sql.rowset; import java.security.AccessController; import java.security.PrivilegedAction; import java.sql.SQLException; import java.util.PropertyPermission; import java.util.ServiceConfigurationError; import java.util.ServiceLoader; import sun.reflect.misc.ReflectUtil; /** * A factory API that enables applications to obtain a * {@code RowSetFactory} implementation that can be used to create different * types of {@code RowSet} implementations. * <p> * Example: * </p> * <pre> * RowSetFactory aFactory = RowSetProvider.newFactory(); * CachedRowSet crs = aFactory.createCachedRowSet(); * ... * RowSetFactory rsf = RowSetProvider.newFactory("com.sun.rowset.RowSetFactoryImpl", null); * WebRowSet wrs = rsf.createWebRowSet(); * </pre> *<p> * Tracing of this class may be enabled by setting the System property * {@code javax.sql.rowset.RowSetFactory.debug} to any value but {@code false}. * </p> * * @author Lance Andersen * @since 1.7 */ public class RowSetProvider { private static final String ROWSET_DEBUG_PROPERTY = "javax.sql.rowset.RowSetProvider.debug"; private static final String ROWSET_FACTORY_IMPL = "com.sun.rowset.RowSetFactoryImpl"; private static final String ROWSET_FACTORY_NAME = "javax.sql.rowset.RowSetFactory"; /** * Internal debug flag. */ private static boolean debug = true; static { // Check to see if the debug property is set String val = getSystemProperty(ROWSET_DEBUG_PROPERTY); // Allow simply setting the prop to turn on debug debug = val != null && !"false".equals(val); } /** * RowSetProvider constructor */ protected RowSetProvider() { } /** * <p>Creates a new instance of a <code>RowSetFactory</code> * implementation. This method uses the following * look up order to determine * the <code>RowSetFactory</code> implementation class to load:</p> * <ul> * <li> * The System property {@code javax.sql.rowset.RowSetFactory}. For example: * <ul> * <li> * -Djavax.sql.rowset.RowSetFactory=com.sun.rowset.RowSetFactoryImpl * </li> * </ul> * <li> * The {@link ServiceLoader} API. The {@code ServiceLoader} API will look * for a class name in the file * {@code META-INF/services/javax.sql.rowset.RowSetFactory} * in jars available to the runtime. For example, to have the RowSetFactory * implementation {@code com.sun.rowset.RowSetFactoryImpl } loaded, the * entry in {@code META-INF/services/javax.sql.rowset.RowSetFactory} would be: * <ul> * <li> * {@code com.sun.rowset.RowSetFactoryImpl } * </li> * </ul> * </li> * <li> * Platform default <code>RowSetFactory</code> instance. * </li> * </ul> * * <p>Once an application has obtained a reference to a {@code RowSetFactory}, * it can use the factory to obtain RowSet instances.</p> * * @return New instance of a <code>RowSetFactory</code> * * @throws SQLException if the default factory class cannot be loaded, * instantiated. The cause will be set to actual Exception * * @see ServiceLoader * @since 1.7 */ public static RowSetFactory newFactory() throws SQLException { // Use the system property first RowSetFactory factory = null; String factoryClassName = null; try { trace("Checking for Rowset System Property..."); factoryClassName = getSystemProperty(ROWSET_FACTORY_NAME); if (factoryClassName != null) { trace("Found system property, value=" + factoryClassName); if (factoryClassName.equals(ROWSET_FACTORY_IMPL)) { return defaultRowSetFactory(); } // getFactoryClass takes care of adding the read edge if // necessary @SuppressWarnings("deprecation") Object o = getFactoryClass(factoryClassName, null, false).newInstance(); factory = (RowSetFactory) o; } } catch (Exception e) { throw new SQLException("RowSetFactory: " + factoryClassName + " could not be instantiated: ", e); } // Check to see if we found the RowSetFactory via a System property if (factory == null) { // If the RowSetFactory is not found via a System Property, now // look it up via the ServiceLoader API and if not found, use the // Java SE default. factory = loadViaServiceLoader(); } return factory == null ? defaultRowSetFactory() : factory; } private static RowSetFactory defaultRowSetFactory() { return new com.sun.rowset.RowSetFactoryImpl(); } /** * <p>Creates a new instance of a <code>RowSetFactory</code> from the * specified factory class name. * 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> * * <p>Once an application has obtained a reference to a <code>RowSetFactory</code> * it can use the factory to obtain RowSet instances.</p> * * @param factoryClassName fully qualified factory class name that * provides an implementation of <code>javax.sql.rowset.RowSetFactory</code>. * * @param cl <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>RowSetFactory</code> * * @throws SQLException if <code>factoryClassName</code> is * <code>null</code>, or the factory class cannot be loaded, instantiated. * * @see #newFactory() * * @since 1.7 */ public static RowSetFactory newFactory(String factoryClassName, ClassLoader cl) throws SQLException { trace("***In newInstance()"); if (factoryClassName == null) { throw new SQLException("Error: factoryClassName cannot be null"); } try { ReflectUtil.checkPackageAccess(factoryClassName); } catch (java.security.AccessControlException e) { throw new SQLException("Access Exception", e); } try { // getFactoryClass takes care of adding the read edge if // necessary Class<?> providerClass = getFactoryClass(factoryClassName, cl, false); @SuppressWarnings("deprecation") RowSetFactory instance = (RowSetFactory) providerClass.newInstance(); if (debug) { trace("Created new instance of " + providerClass + " using ClassLoader: " + cl); } return instance; } catch (ClassNotFoundException x) { throw new SQLException("Provider " + factoryClassName + " not found", x); } catch (Exception x) { throw new SQLException("Provider " + factoryClassName + " could not be instantiated: " + x, x); } } /* * Returns the class loader to be used. * @return The ClassLoader to use. * */ static private ClassLoader getContextClassLoader() throws SecurityException { return AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() { public ClassLoader run() { ClassLoader cl = null; cl = Thread.currentThread().getContextClassLoader(); if (cl == null) { cl = ClassLoader.getSystemClassLoader(); } return cl; } }); } /** * Attempt to load a class using the class loader supplied. If that fails * and fall back is enabled, the current (i.e. bootstrap) class loader is * tried. * * If the class loader supplied is <code>null</code>, first try using the * context class loader followed by the current class loader. * @return The class which was loaded */ static private Class<?> getFactoryClass(String factoryClassName, ClassLoader cl, boolean doFallback) throws ClassNotFoundException { Class<?> factoryClass = null; try { if (cl == null) { cl = getContextClassLoader(); if (cl == null) { throw new ClassNotFoundException(); } else { factoryClass = cl.loadClass(factoryClassName); } } else { factoryClass = cl.loadClass(factoryClassName); } } catch (ClassNotFoundException e) { if (doFallback) { // Use current class loader factoryClass = Class.forName(factoryClassName, true, RowSetFactory.class.getClassLoader()); } else { throw e; } } ReflectUtil.checkPackageAccess(factoryClass); return factoryClass; } /** * Use the ServiceLoader mechanism to load the default RowSetFactory * @return default RowSetFactory Implementation */ static private RowSetFactory loadViaServiceLoader() throws SQLException { RowSetFactory theFactory = null; try { trace("***in loadViaServiceLoader():"); for (RowSetFactory factory : ServiceLoader.load(javax.sql.rowset.RowSetFactory.class)) { trace(" Loading done by the java.util.ServiceLoader :" + factory.getClass().getName()); theFactory = factory; break; } } catch (ServiceConfigurationError e) { throw new SQLException( "RowSetFactory: Error locating RowSetFactory using Service " + "Loader API: " + e, e); } return theFactory; } /** * Returns the requested System Property. If a {@code SecurityException} * occurs, just return NULL * @param propName - System property to retrieve * @return The System property value or NULL if the property does not exist * or a {@code SecurityException} occurs. */ static private String getSystemProperty(final String propName) { String property = null; try { property = AccessController.doPrivileged(new PrivilegedAction<String>() { public String run() { return System.getProperty(propName); } }, null, new PropertyPermission(propName, "read")); } catch (SecurityException se) { trace("error getting " + propName + ": " + se); if (debug) { se.printStackTrace(); } } return property; } /** * Debug routine which will output tracing if the System Property * -Djavax.sql.rowset.RowSetFactory.debug is set * @param msg - The debug message to display */ private static void trace(String msg) { if (debug) { System.err.println("###RowSets: " + msg); } } }