/*

 * 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);

        }

    }

}