Java tutorial
/* * Copyright (c) 1996, 2018, 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 java.sql; import java.util.ArrayList; import java.util.Collections; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.ServiceLoader; import java.security.AccessController; import java.security.PrivilegedAction; import java.util.concurrent.CopyOnWriteArrayList; import java.util.stream.Stream; import jdk.internal.reflect.CallerSensitive; import jdk.internal.reflect.Reflection; /** * The basic service for managing a set of JDBC drivers. * <p> * <strong>NOTE:</strong> The {@link javax.sql.DataSource} interface, provides * another way to connect to a data source. * The use of a {@code DataSource} object is the preferred means of * connecting to a data source. * <P> * As part of its initialization, the {@code DriverManager} class will * attempt to load available JDBC drivers by using: * <ul> * <li>The {@code jdbc.drivers} system property which contains a * colon separated list of fully qualified class names of JDBC drivers. Each * driver is loaded using the {@linkplain ClassLoader#getSystemClassLoader * system class loader}: * <ul> * <li>{@code jdbc.drivers=foo.bah.Driver:wombat.sql.Driver:bad.taste.ourDriver} * </ul> * * <li>Service providers of the {@code java.sql.Driver} class, that are loaded * via the {@linkplain ServiceLoader#load service-provider loading} mechanism. *</ul> * * @implNote * {@code DriverManager} initialization is done lazily and looks up service * providers using the thread context class loader. The drivers loaded and * available to an application will depend on the thread context class loader of * the thread that triggers driver initialization by {@code DriverManager}. * * <P>When the method {@code getConnection} is called, * the {@code DriverManager} will attempt to * locate a suitable driver from amongst those loaded at * initialization and those loaded explicitly using the same class loader * as the current application. * * @see Driver * @see Connection * @since 1.1 */ public class DriverManager { // List of registered JDBC drivers private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>(); private static volatile int loginTimeout = 0; private static volatile java.io.PrintWriter logWriter = null; private static volatile java.io.PrintStream logStream = null; // Used in println() to synchronize logWriter private final static Object logSync = new Object(); // Used in ensureDriversInitialized() to synchronize driversInitialized private final static Object lockForInitDrivers = new Object(); private static volatile boolean driversInitialized; private static final String JDBC_DRIVERS_PROPERTY = "jdbc.drivers"; /* Prevent the DriverManager class from being instantiated. */ private 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"); /** * The {@code SQLPermission} constant that allows the * un-register a registered JDBC driver. * @since 1.8 */ final static SQLPermission DEREGISTER_DRIVER_PERMISSION = new SQLPermission("deregisterDriver"); //--------------------------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> * If a security manager exists, its {@code checkPermission} * method is first called with a {@code SQLPermission("setLog")} * permission to check that the caller is allowed to call {@code setLogWriter}. * * @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} method denies permission to set 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. *<p> * <B>Note:</B> If a property is specified as part of the {@code url} and * is also specified in the {@code Properties} object, it is * implementation-defined as to which value will take precedence. * For maximum portability, an application should only specify a * property once. * * @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 or the url is * {@code null} * @throws SQLTimeoutException when the driver has determined that the * timeout value specified by the {@code setLoginTimeout} method * has been exceeded and has at least tried to cancel the * current database connection attempt */ @CallerSensitive public static Connection getConnection(String url, java.util.Properties info) throws SQLException { return (getConnection(url, info, Reflection.getCallerClass())); } /** * 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. *<p> * <B>Note:</B> If the {@code user} or {@code password} property are * also specified as part of the {@code url}, it is * implementation-defined as to which value will take precedence. * For maximum portability, an application should only specify a * property once. * * @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 or the url is * {@code null} * @throws SQLTimeoutException when the driver has determined that the * timeout value specified by the {@code setLoginTimeout} method * has been exceeded and has at least tried to cancel the * current database connection attempt */ @CallerSensitive public static Connection getConnection(String url, String user, String password) throws SQLException { java.util.Properties info = new java.util.Properties(); if (user != null) { info.put("user", user); } if (password != null) { info.put("password", password); } return (getConnection(url, info, Reflection.getCallerClass())); } /** * 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 or the url is * {@code null} * @throws SQLTimeoutException when the driver has determined that the * timeout value specified by the {@code setLoginTimeout} method * has been exceeded and has at least tried to cancel the * current database connection attempt */ @CallerSensitive public static Connection getConnection(String url) throws SQLException { java.util.Properties info = new java.util.Properties(); return (getConnection(url, info, Reflection.getCallerClass())); } /** * 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 */ @CallerSensitive public static Driver getDriver(String url) throws SQLException { println("DriverManager.getDriver(\"" + url + "\")"); ensureDriversInitialized(); Class<?> callerClass = Reflection.getCallerClass(); // Walk through the loaded registeredDrivers attempting to locate someone // who understands the given URL. for (DriverInfo aDriver : registeredDrivers) { // If the caller does not have permission to load the driver then // skip it. if (isDriverAllowed(aDriver.driver, callerClass)) { try { if (aDriver.driver.acceptsURL(url)) { // Success! println("getDriver returning " + aDriver.driver.getClass().getName()); return (aDriver.driver); } } catch (SQLException sqe) { // Drop through and try the next driver. } } else { println(" skipping: " + aDriver.driver.getClass().getName()); } } println("getDriver: no suitable driver"); throw new SQLException("No suitable driver", "08001"); } /** * Registers the given driver with the {@code DriverManager}. * A newly-loaded driver class should call * the method {@code registerDriver} to make itself * known to the {@code DriverManager}. If the driver is currently * registered, no action is taken. * * @param driver the new JDBC Driver that is to be registered with the * {@code DriverManager} * @exception SQLException if a database access error occurs * @exception NullPointerException if {@code driver} is null */ public static void registerDriver(java.sql.Driver driver) throws SQLException { registerDriver(driver, null); } /** * Registers the given driver with the {@code DriverManager}. * A newly-loaded driver class should call * the method {@code registerDriver} to make itself * known to the {@code DriverManager}. If the driver is currently * registered, no action is taken. * * @param driver the new JDBC Driver that is to be registered with the * {@code DriverManager} * @param da the {@code DriverAction} implementation to be used when * {@code DriverManager#deregisterDriver} is called * @exception SQLException if a database access error occurs * @exception NullPointerException if {@code driver} is null * @since 1.8 */ public static void registerDriver(java.sql.Driver driver, DriverAction da) throws SQLException { /* Register the driver if it has not already been added to our list */ if (driver != null) { registeredDrivers.addIfAbsent(new DriverInfo(driver, da)); } else { // This is for compatibility with the original DriverManager throw new NullPointerException(); } println("registerDriver: " + driver); } /** * Removes the specified driver from the {@code DriverManager}'s list of * registered drivers. * <p> * If a {@code null} value is specified for the driver to be removed, then no * action is taken. * <p> * If a security manager exists, its {@code checkPermission} * method is first called with a {@code SQLPermission("deregisterDriver")} * permission to check that the caller is allowed to deregister a JDBC Driver. * <p> * If the specified driver is not found in the list of registered drivers, * then no action is taken. If the driver was found, it will be removed * from the list of registered drivers. * <p> * If a {@code DriverAction} instance was specified when the JDBC driver was * registered, its deregister method will be called * prior to the driver being removed from the list of registered drivers. * * @param driver the JDBC Driver to remove * @exception SQLException if a database access error occurs * @throws SecurityException if a security manager exists and its * {@code checkPermission} method denies permission to deregister a driver. * * @see SecurityManager#checkPermission */ @CallerSensitive public static void deregisterDriver(Driver driver) throws SQLException { if (driver == null) { return; } SecurityManager sec = System.getSecurityManager(); if (sec != null) { sec.checkPermission(DEREGISTER_DRIVER_PERMISSION); } println("DriverManager.deregisterDriver: " + driver); DriverInfo aDriver = new DriverInfo(driver, null); synchronized (lockForInitDrivers) { if (registeredDrivers.contains(aDriver)) { if (isDriverAllowed(driver, Reflection.getCallerClass())) { DriverInfo di = registeredDrivers.get(registeredDrivers.indexOf(aDriver)); // If a DriverAction was specified, Call it to notify the // driver that it has been deregistered if (di.action() != null) { di.action().deregister(); } registeredDrivers.remove(aDriver); } else { // If the caller does not have permission to load the driver then // throw a SecurityException. throw new SecurityException(); } } else { println(" couldn't find driver to unload"); } } } /** * 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 * @see #drivers() */ @CallerSensitive public static Enumeration<Driver> getDrivers() { ensureDriversInitialized(); return Collections.enumeration(getDrivers(Reflection.getCallerClass())); } /** * Retrieves a Stream with all of the currently loaded JDBC drivers * to which the current caller has access. * * @return the stream of JDBC Drivers loaded by the caller's class loader * @since 9 */ @CallerSensitive public static Stream<Driver> drivers() { ensureDriversInitialized(); return getDrivers(Reflection.getCallerClass()).stream(); } private static List<Driver> getDrivers(Class<?> callerClass) { List<Driver> result = new ArrayList<>(); // Walk through the loaded registeredDrivers. for (DriverInfo aDriver : registeredDrivers) { // If the caller does not have permission to load the driver then // skip it. if (isDriverAllowed(aDriver.driver, callerClass)) { result.add(aDriver.driver); } else { println(" skipping: " + aDriver.getClass().getName()); } } return result; } /** * Sets the maximum time in seconds that a driver will wait * while attempting to connect to a database once the driver has * been identified. * * @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> * If a security manager exists, its {@code checkPermission} * method is first called with a {@code SQLPermission("setLog")} * permission to check that the caller is allowed to call {@code setLogStream}. * * @param out the new logging/tracing PrintStream; to disable, set to <code>null</code> * @deprecated Use {@code setLogWriter} * @throws SecurityException if a security manager exists and its * {@code checkPermission} method denies permission to set the log stream. * @see SecurityManager#checkPermission * @see #getLogStream */ @Deprecated(since = "1.2") 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 Use {@code getLogWriter} * @see #setLogStream */ @Deprecated(since = "1.2") 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(); } } } //------------------------------------------------------------------------ // Indicates whether the class object that would be created if the code calling // DriverManager is accessible. private static boolean isDriverAllowed(Driver driver, Class<?> caller) { ClassLoader callerCL = caller != null ? caller.getClassLoader() : null; return isDriverAllowed(driver, callerCL); } private static boolean isDriverAllowed(Driver driver, ClassLoader classLoader) { boolean result = false; if (driver != null) { Class<?> aClass = null; try { aClass = Class.forName(driver.getClass().getName(), true, classLoader); } catch (Exception ex) { result = false; } result = (aClass == driver.getClass()) ? true : false; } return result; } /* * Load the initial JDBC drivers by checking the System property * jdbc.drivers and then use the {@code ServiceLoader} mechanism */ private static void ensureDriversInitialized() { if (driversInitialized) { return; } synchronized (lockForInitDrivers) { if (driversInitialized) { return; } String drivers; try { drivers = AccessController.doPrivileged(new PrivilegedAction<String>() { public String run() { return System.getProperty(JDBC_DRIVERS_PROPERTY); } }); } 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<Void>() { public Void run() { ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class); Iterator<Driver> 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 * and load the service. * * Adding a try catch block to catch those runtime errors * if driver not available in classpath but it's * packaged as service and that service is there in classpath. */ try { while (driversIterator.hasNext()) { driversIterator.next(); } } catch (Throwable t) { // Do nothing } return null; } }); println("DriverManager.initialize: jdbc.drivers = " + drivers); if (drivers != null && !drivers.isEmpty()) { String[] driversList = drivers.split(":"); println("number of Drivers:" + driversList.length); for (String aDriver : driversList) { try { println("DriverManager.Initialize: loading " + aDriver); Class.forName(aDriver, true, ClassLoader.getSystemClassLoader()); } catch (Exception ex) { println("DriverManager.Initialize: load failed: " + ex); } } } driversInitialized = true; println("JDBC DriverManager initialized"); } } // Worker method called by the public getConnection() methods. private static Connection getConnection(String url, java.util.Properties info, Class<?> caller) throws SQLException { /* * When callerCl is null, we should check the application's * (which is invoking this class indirectly) * classloader, so that the JDBC driver class outside rt.jar * can be loaded from here. */ ClassLoader callerCL = caller != null ? caller.getClassLoader() : null; if (callerCL == null || callerCL == ClassLoader.getPlatformClassLoader()) { callerCL = Thread.currentThread().getContextClassLoader(); } if (url == null) { throw new SQLException("The url cannot be null", "08001"); } println("DriverManager.getConnection(\"" + url + "\")"); ensureDriversInitialized(); // Walk through the loaded registeredDrivers attempting to make a connection. // Remember the first exception that gets raised so we can reraise it. SQLException reason = null; for (DriverInfo aDriver : registeredDrivers) { // If the caller does not have permission to load the driver then // skip it. if (isDriverAllowed(aDriver.driver, callerCL)) { try { println(" trying " + aDriver.driver.getClass().getName()); Connection con = aDriver.driver.connect(url, info); if (con != null) { // Success! println("getConnection returning " + aDriver.driver.getClass().getName()); return (con); } } catch (SQLException ex) { if (reason == null) { reason = ex; } } } else { println(" skipping: " + aDriver.getClass().getName()); } } // if we got here nobody could connect. if (reason != null) { println("getConnection failed: " + reason); throw reason; } println("getConnection: no suitable driver found for " + url); throw new SQLException("No suitable driver found for " + url, "08001"); } } /* * Wrapper class for registered Drivers in order to not expose Driver.equals() * to avoid the capture of the Driver it being compared to as it might not * normally have access. */ class DriverInfo { final Driver driver; DriverAction da; DriverInfo(Driver driver, DriverAction action) { this.driver = driver; da = action; } @Override public boolean equals(Object other) { return (other instanceof DriverInfo) && this.driver == ((DriverInfo) other).driver; } @Override public int hashCode() { return driver.hashCode(); } @Override public String toString() { return ("driver[className=" + driver + "]"); } DriverAction action() { return da; } }