drivermanager.java

java数据库源代码 请看看啊 提点宝贵的意见

	for (i = 0; i < drivers.size(); i++) {
	    di = (DriverInfo)drivers.elementAt(i);
	    if (di.driver == driver) {
		break;
	    }
	}
	// If we can't find the driver just return.
	if (i >= drivers.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.
	drivers.removeElementAt(i);
      
    }

    /**
     * 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 synchronized java.util.Enumeration getDrivers() {
        java.util.Vector result = new java.util.Vector();

        if (!initialized) {
            initialize();
        }

        // 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
     * @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 synchronized 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) java.security.AccessController.doPrivileged(
		new sun.security.action.GetPropertyAction("jdbc.drivers"));
        } catch (Exception ex) {
            drivers = null;
        }
        println("DriverManager.initialize: jdbc.drivers = " + drivers);
        if (drivers == null) {
            return;
        }
        while (drivers.length() != 0) {
            int x = drivers.indexOf(':');
            String driver;
            if (x < 0) {
                driver = drivers;
                drivers = "";
            } else {
                driver = drivers.substring(0, x);
                drivers = drivers.substring(x+1);
            }
            if (driver.length() == 0) {
                continue;
            }
            try {
                println("DriverManager.Initialize: loading " + driver);
                Class.forName(driver, true,
			      ClassLoader.getSystemClassLoader());
            } catch (Exception ex) {
                println("DriverManager.Initialize: load failed: " + ex);
            }
        }
    }


    //  Worker method called by the public getConnection() methods.
    private static synchronized Connection getConnection(
	String url, java.util.Properties info, ClassLoader callerCL) throws SQLException {
	if(url == null) {
	    throw new SQLException("The url cannot be null", "08001");
	}
    
	println("DriverManager.getConnection(\"" + url + "\")");
    
	if (!initialized) {
	    initialize();
	}

	// Walk through the loaded drivers attempting to make a connection.
	// Remember the first exception that gets raised so we can reraise it.
	SQLException reason = null;
	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);
		Connection result = di.driver.connect(url, info);
		if (result != null) {
		    // Success!
		    println("getConnection returning " + di);
		    return (result);
		}
	    } catch (SQLException ex) {
		if (reason == null) {
		    reason = ex;
		}
	    }
	}
    
	// if we got here nobody could connect.
	if (reason != null)    {
	    println("getConnection failed: " + reason);
	    throw reason;
	}
    
	println("getConnection: no suitable driver");
	throw new SQLException("No suitable driver", "08001");
    }


    // Class initialization.
    static void initialize() {
        if (initialized) {
            return;
        }
        initialized = true;
        loadInitialDrivers();
        println("JDBC DriverManager initialized");
    }

    // Prevent the DriverManager class from being instantiated.
    private DriverManager(){}

    private static java.util.Vector drivers = new java.util.Vector();
    private static int loginTimeout = 0;
    private static java.io.PrintWriter logWriter = null;
    private static java.io.PrintStream logStream = null;
    private static boolean initialized = false;

    private static Object logSync = new Object();

    // Returns the caller's class loader, or null if none
    private static native ClassLoader getCallerClassLoader();

}


// DriverInfo is a package-private support class.
class DriverInfo {
    Driver         driver;
    Class          driverClass;
    String         driverClassName;

    public String toString() {
	return ("driver[className=" + driverClassName + "," + driver + "]");
    }
}