/*

 * Copyright 1996-2006 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.sql;

import java.util.Iterator;

import java.sql.Driver;

import java.util.ServiceLoader;

import java.security.AccessController;

import java.security.PrivilegedAction;

/**

 * <P>The basic service for managing a set of JDBC drivers.<br>

 * <B>NOTE:</B> The {@link <code>DataSource</code>} interface, new in the

 * JDBC 2.0 API, provides another way to connect to a data source.

 * The use of a <code>DataSource</code> object is the preferred means of

 * connecting to a data source.

 *

 * <P>As part of its initialization, the <code>DriverManager</code> class will

 * attempt to load the driver classes referenced in the "jdbc.drivers"

 * system property. This allows a user to customize the JDBC Drivers

 * used by their applications. For example in your

 * ~/.hotjava/properties file you might specify:

 * <pre>

 * <CODE>jdbc.drivers=foo.bah.Driver:wombat.sql.Driver:bad.taste.ourDriver</CODE>

 * </pre>

 *<P> The <code>DriverManager</code> methods <code>getConnection</code> and

 * <code>getDrivers</code> have been enhanced to support the Java Standard Edition

 * <a href="../../../technotes/guides/jar/jar.html#Service%20Provider">Service Provider</a> mechanism. JDBC 4.0 Drivers must

 * include the file <code>META-INF/services/java.sql.Driver</code>. This file contains the name of the JDBC drivers

 * implementation of <code>java.sql.Driver</code>.  For example, to load the <code>my.sql.Driver</code> class,

 * the <code>META-INF/services/java.sql.Driver</code> file would contain the entry:

 * <pre>

 * <code>my.sql.Driver</code>

 * </pre>

 *

 * <P>Applications no longer need to explictly load JDBC drivers using <code>Class.forName()</code>. Existing programs

 * which currently load JDBC drivers using <code>Class.forName()</code> will continue to work without

 * modification.

 *

 * <P>When the method <code>getConnection</code> is called,

 * the <code>DriverManager</code> will attempt to

 * locate a suitable driver from amongst those loaded at

 * initialization and those loaded explicitly using the same classloader

 * as the current applet or application.

 *

 * <P>

 * Starting with the Java 2 SDK, Standard Edition, version 1.3, a

 * logging stream can be set only if the proper

 * permission has been granted.  Normally this will be done with

 * the tool PolicyTool, which can be used to grant <code>permission

 * java.sql.SQLPermission "setLog"</code>.

 * @see Driver

 * @see Connection

 */

public class DriverManager {

    /**

     * The <code>SQLPermission</code> constant that allows the

     * setting of the logging stream.

     * @since 1.3

     */

    final static SQLPermission SET_LOG_PERMISSION =

        new SQLPermission("setLog");

    //--------------------------JDBC 2.0-----------------------------

    /**

     * Retrieves the log writer.

     *

     * The <code>getLogWriter</code> and <code>setLogWriter</code>

     * methods should be used instead

     * of the <code>get/setlogStream</code> methods, which are deprecated.

     * @return a <code>java.io.PrintWriter</code> object

     * @see #setLogWriter

     * @since 1.2

     */

    public static java.io.PrintWriter getLogWriter() {

            return logWriter;

    }

    /**

     * Sets the logging/tracing <code>PrintWriter</code> object

     * that is used by the <code>DriverManager</code> and all drivers.

     * <P>

     * There is a minor versioning problem created by the introduction

     * of the method <code>setLogWriter</code>.  The

     * method <code>setLogWriter</code> cannot create a <code>PrintStream</code> object

     * that will be returned by <code>getLogStream</code>---the Java platform does

     * not provide a backward conversion.  As a result, a new application

     * that uses <code>setLogWriter</code> and also uses a JDBC 1.0 driver that uses

     * <code>getLogStream</code> will likely not see debugging information written

     * by that driver.

     *<P>

     * Starting with the Java 2 SDK, Standard Edition, version 1.3 release, this method checks

     * to see that there is an <code>SQLPermission</code> object before setting

     * the logging stream.  If a <code>SecurityManager</code> exists and its

     * <code>checkPermission</code> method denies setting the log writer, this

     * method throws a <code>java.lang.SecurityException</code>.

     *

     * @param out the new logging/tracing <code>PrintStream</code> object;

     *      <code>null</code> to disable logging and tracing

     * @throws SecurityException

     *    if a security manager exists and its

     *    <code>checkPermission</code> method denies

     *    setting the log writer

     *

     * @see SecurityManager#checkPermission

     * @see #getLogWriter

     * @since 1.2

     */

    public static void setLogWriter(java.io.PrintWriter out) {

        SecurityManager sec = System.getSecurityManager();

        if (sec != null) {

            sec.checkPermission(SET_LOG_PERMISSION);

        }

            logStream = null;

            logWriter = out;

    }

    //---------------------------------------------------------------

    /**

     * Attempts to establish a connection to the given database URL.

     * The <code>DriverManager</code> attempts to select an appropriate driver from

     * the set of registered JDBC drivers.

     *

     * @param url a database url of the form

     * <code> jdbc:<em>subprotocol</em>:<em>subname</em></code>

     * @param info a list of arbitrary string tag/value pairs as

     * connection arguments; normally at least a "user" and

     * "password" property should be included

     * @return a Connection to the URL

     * @exception SQLException if a database access error occurs

     */

    public static Connection getConnection(String url,

        java.util.Properties info) throws SQLException {

        // Gets the classloader of the code that called this method, may

        // be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        return (getConnection(url, info, callerCL));

    }

    /**

     * Attempts to establish a connection to the given database URL.

     * The <code>DriverManager</code> attempts to select an appropriate driver from

     * the set of registered JDBC drivers.

     *

     * @param url a database url of the form

     * <code>jdbc:<em>subprotocol</em>:<em>subname</em></code>

     * @param user the database user on whose behalf the connection is being

     *   made

     * @param password the user's password

     * @return a connection to the URL

     * @exception SQLException if a database access error occurs

     */

    public static Connection getConnection(String url,

        String user, String password) throws SQLException {

        java.util.Properties info = new java.util.Properties();

        // Gets the classloader of the code that called this method, may

        // be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        if (user != null) {

            info.put("user", user);

        }

        if (password != null) {

            info.put("password", password);

        }

        return (getConnection(url, info, callerCL));

    }

    /**

     * Attempts to establish a connection to the given database URL.

     * The <code>DriverManager</code> attempts to select an appropriate driver from

     * the set of registered JDBC drivers.

     *

     * @param url a database url of the form

     *  <code> jdbc:<em>subprotocol</em>:<em>subname</em></code>

     * @return a connection to the URL

     * @exception SQLException if a database access error occurs

     */

    public static Connection getConnection(String url)

        throws SQLException {

        java.util.Properties info = new java.util.Properties();

        // Gets the classloader of the code that called this method, may

        // be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        return (getConnection(url, info, callerCL));

    }

    /**

     * Attempts to locate a driver that understands the given URL.

     * The <code>DriverManager</code> attempts to select an appropriate driver from

     * the set of registered JDBC drivers.

     *

     * @param url a database URL of the form

     *     <code>jdbc:<em>subprotocol</em>:<em>subname</em></code>

     * @return a <code>Driver</code> object representing a driver

     * that can connect to the given URL

     * @exception SQLException if a database access error occurs

     */

    public static Driver getDriver(String url)

        throws SQLException {

        java.util.Vector drivers = null;

        println("DriverManager.getDriver(\"" + url + "\")");

        if (!initialized) {

            initialize();

        }

        synchronized (DriverManager.class){

            // use the read copy of the drivers vector

            drivers = readDrivers;

        }

        // Gets the classloader of the code that called this method, may

        // be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        // Walk through the loaded drivers attempting to locate someone

        // who understands the given URL.

        for (int i = 0; i < drivers.size(); i++) {

            DriverInfo di = (DriverInfo)drivers.elementAt(i);

            // If the caller does not have permission to load the driver then

            // skip it.

            if ( getCallerClass(callerCL, di.driverClassName ) !=

                 di.driverClass ) {

                println("    skipping: " + di);

                continue;

            }

            try {

                println("    trying " + di);

                if (di.driver.acceptsURL(url)) {

                    // Success!

                    println("getDriver returning " + di);

                    return (di.driver);

                }

            } catch (SQLException ex) {

                // Drop through and try the next driver.

            }

        }

        println("getDriver: no suitable driver");

        throw new SQLException("No suitable driver", "08001");

    }

    /**

     * Registers the given driver with the <code>DriverManager</code>.

     * A newly-loaded driver class should call

     * the method <code>registerDriver</code> to make itself

     * known to the <code>DriverManager</code>.

     *

     * @param driver the new JDBC Driver that is to be registered with the

     *               <code>DriverManager</code>

     * @exception SQLException if a database access error occurs

     */

    public static synchronized void registerDriver(java.sql.Driver driver)

        throws SQLException {

        if (!initialized) {

            initialize();

        }

        DriverInfo di = new DriverInfo();

        di.driver = driver;

        di.driverClass = driver.getClass();

        di.driverClassName = di.driverClass.getName();

        // Not Required -- drivers.addElement(di);

        writeDrivers.addElement(di);

        println("registerDriver: " + di);

        /* update the read copy of drivers vector */

        readDrivers = (java.util.Vector) writeDrivers.clone();

    }

    /**

     * Drops a driver from the <code>DriverManager</code>'s list.

     *  Applets can only deregister drivers from their own classloaders.

     *

     * @param driver the JDBC Driver to drop

     * @exception SQLException if a database access error occurs

     */

    public static synchronized void deregisterDriver(Driver driver)

        throws SQLException {

        // Gets the classloader of the code that called this method,

        // may be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        println("DriverManager.deregisterDriver: " + driver);

        // Walk through the loaded drivers.

        int i;

        DriverInfo di = null;

        for (i = 0; i < writeDrivers.size(); i++) {

            di = (DriverInfo)writeDrivers.elementAt(i);

            if (di.driver == driver) {

                break;

            }

        }

        // If we can't find the driver just return.

        if (i >= writeDrivers.size()) {

            println("    couldn't find driver to unload");

            return;

        }

        // If the caller does not have permission to load the driver then

        // throw a security exception.

        if (getCallerClass(callerCL, di.driverClassName ) != di.driverClass ) {

            throw new SecurityException();

        }

        // Remove the driver.  Other entries in drivers get shuffled down.

        writeDrivers.removeElementAt(i);

        /* update the read copy of drivers vector */

        readDrivers = (java.util.Vector) writeDrivers.clone();

    }

    /**

     * Retrieves an Enumeration with all of the currently loaded JDBC drivers

     * to which the current caller has access.

     *

     * <P><B>Note:</B> The classname of a driver can be found using

     * <CODE>d.getClass().getName()</CODE>

     *

     * @return the list of JDBC Drivers loaded by the caller's class loader

     */

    public static java.util.Enumeration<Driver> getDrivers() {

        java.util.Vector<Driver> result = new java.util.Vector<Driver>();

        java.util.Vector drivers = null;

        if (!initialized) {

            initialize();

        }

        synchronized (DriverManager.class){

            // use the readcopy of drivers

            drivers  = readDrivers;

       }

        // Gets the classloader of the code that called this method, may

        // be null.

        ClassLoader callerCL = DriverManager.getCallerClassLoader();

        // Walk through the loaded drivers.

        for (int i = 0; i < drivers.size(); i++) {

            DriverInfo di = (DriverInfo)drivers.elementAt(i);

            // If the caller does not have permission to load the driver then

            // skip it.

            if ( getCallerClass(callerCL, di.driverClassName ) != di.driverClass ) {

                println("    skipping: " + di);

                continue;

            }

            result.addElement(di.driver);

        }

        return (result.elements());

    }

    /**

     * Sets the maximum time in seconds that a driver will wait

     * while attempting to connect to a database.

     *

     * @param seconds the login time limit in seconds; zero means there is no limit

     * @see #getLoginTimeout

     */

    public static void setLoginTimeout(int seconds) {

        loginTimeout = seconds;

    }

    /**

     * Gets the maximum time in seconds that a driver can wait

     * when attempting to log in to a database.

     *

     * @return the driver login time limit in seconds

     * @see #setLoginTimeout

     */

    public static int getLoginTimeout() {

        return (loginTimeout);

    }

    /**

     * Sets the logging/tracing PrintStream that is used

     * by the <code>DriverManager</code>

     * and all drivers.

     *<P>

     * In the Java 2 SDK, Standard Edition, version 1.3 release, this method checks

     * to see that there is an <code>SQLPermission</code> object before setting

     * the logging stream.  If a <code>SecurityManager</code> exists and its

     * <code>checkPermission</code> method denies setting the log writer, this

     * method throws a <code>java.lang.SecurityException</code>.

     *

     * @param out the new logging/tracing PrintStream; to disable, set to <code>null</code>

     * @deprecated

     * @throws SecurityException if a security manager exists and its

     *    <code>checkPermission</code> method denies setting the log stream

     *

     * @see SecurityManager#checkPermission

     * @see #getLogStream

     */

    public static void setLogStream(java.io.PrintStream out) {

        SecurityManager sec = System.getSecurityManager();

        if (sec != null) {

            sec.checkPermission(SET_LOG_PERMISSION);

        }

        logStream = out;

        if ( out != null )

            logWriter = new java.io.PrintWriter(out);

        else

            logWriter = null;

    }

    /**

     * Retrieves the logging/tracing PrintStream that is used by the <code>DriverManager</code>

     * and all drivers.

     *

     * @return the logging/tracing PrintStream; if disabled, is <code>null</code>

     * @deprecated

     * @see #setLogStream

     */

    public static java.io.PrintStream getLogStream() {

        return logStream;

    }

    /**

     * Prints a message to the current JDBC log stream.

     *

     * @param message a log or tracing message

     */

    public static void println(String message) {

        synchronized (logSync) {

            if (logWriter != null) {

                logWriter.println(message);

                // automatic flushing is never enabled, so we must do it ourselves

                logWriter.flush();

            }

        }

    }

    //------------------------------------------------------------------------

    // Returns the class object that would be created if the code calling the

    // driver manager had loaded the driver class, or null if the class

    // is inaccessible.

    private static Class getCallerClass(ClassLoader callerClassLoader,

                                        String driverClassName) {

        Class callerC = null;

        try {

            callerC = Class.forName(driverClassName, true, callerClassLoader);

        }

        catch (Exception ex) {

            callerC = null;           // being very careful

        }

        return callerC;

    }

    private static void loadInitialDrivers() {

        String drivers;

        try {

            drivers = (String)  AccessController.doPrivileged(new PrivilegedAction() {

                public Object run() {

                    return System.getProperty("jdbc.drivers");

                }

            });

        } catch (Exception ex) {

            drivers = null;

        }

        // If the driver is packaged as a Service Provider, load it.

        // Get all the drivers through the classloader

        // exposed as a java.sql.Driver.class service.

        // ServiceLoader.load() replaces the sun.misc.Providers()

        AccessController.doPrivileged(new PrivilegedAction() {

            public Object run() {

                ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class);

                Iterator driversIterator = loadedDrivers.iterator();

                /* Load these drivers, so that they can be instantiated.

                 * It may be the case that the driver class may not be there

                 * i.e. there may be a packaged driver with the service class

                 * as implementation of java.sql.Driver but the actual class

                 * may be missing. In that case a java.util.ServiceConfigurationError

                 * will be thrown at runtime by the VM trying to locate