drivermanager.java

一个JDBC数据库连接的组件

/*
 * @(#)DriverManager.java	1.12 98/04/24
 *
 * Copyright 1996-1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

package java.sql;

/**
 * <P>The DriverManager provides a basic service for managing a set of
 * JDBC drivers.
 *
 * <P>As part of its initialization, the DriverManager 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:
 * <CODE>jdbc.drivers=foo.bah.Driver:wombat.sql.Driver:bad.taste.ourDriver</CODE>
 *
 * A program can also explicitly load JDBC drivers at any time. For
 * example, the my.sql.Driver is loaded with the following statement:
 * <CODE>Class.forName("my.sql.Driver");</CODE>
 *
 * <P>When getConnection is called the DriverManager 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.
 *
 * @see Driver
 * @see Connection 
 */
public class DriverManager {

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

    /**
     * JDBC 2.0
     *
     * Get the log writer.  
     *
     * The getLogWriter() and setLogWriter() methods should be used instead
     * of the old get/setlogStream() methods.
     */
    public static java.io.PrintWriter getLogWriter() {
      return logWriter;
    }

    /**
     * JDBC 2.0
     *
     * Set the logging/tracing Writer that is used by the DriverManager
     * and all drivers.
     *
     * There is a minor versioning problem introduced by the introduction
     * of setLogWriter().  SetLogWriter() can not create a PrintStream
     * that will be returned by getLogStream()---the Java platform does
     * not provide a backward conversion.  So, a new application
     * that uses setLogWriter() and also uses a JDBC 1.0 driver that uses
     * getLogStream() will likely not see debugging information written 
     * by that driver.
     *
     * @param out the new logging/tracing PrintStream; to disable, set to null
     */
    public static void setLogWriter(java.io.PrintWriter out) {
      logStream = null;
      logWriter = out;
    }

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

    /**
     * Attempt to establish a connection to the given database URL.
     * The DriverManager attempts to select an appropriate driver from
     * the set of registered JDBC drivers.
     *
     * @param url a database url of the form jdbc:<em>subprotocol</em>:<em>subname</em>
     * @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 synchronized Connection getConnection(String url, 
            java.util.Properties info) throws SQLException {
	if(url == null) {
	    throw new SQLException("The url cannot be null", "08001");
	}

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

        if (!initialized) {
            initialize();
        }

        // Figure out the current security context.
        Object currentSecurityContext = getSecurityContext();

        // 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 driver isn't part of the base system and doesn't come
            // from the same security context as the current caller, skip it.
            if (di.securityContext != null && 
                        di.securityContext != currentSecurityContext) {
                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");
    }

    /**
     * Attempt to establish a connection to the given database URL.
     * The DriverManager attempts to select an appropriate driver from
     * the set of registered JDBC drivers.
     *
     * @param url a database url of the form jdbc:<em>subprotocol</em>:<em>subname</em>
     * @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 synchronized 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));
    }

    /**
     * Attempt to establish a connection to the given database URL.
     * The DriverManager attempts to select an appropriate driver from
     * the set of registered JDBC drivers.
     *
     * @param url a database url of the form jdbc:<em>subprotocol</em>:<em>subname</em>
     * @return a Connection to the URL 
     * @exception SQLException if a database-access error occurs.
     */
    public static synchronized Connection getConnection(String url) 
                                    throws SQLException {
        java.util.Properties info = new java.util.Properties();
        return (getConnection(url, info));
    }

    /**
     * Attempt to locate a driver that understands the given URL.
     * The DriverManager attempts to select an appropriate driver from
     * the set of registered JDBC drivers. 
     *
     * @param url a database url of the form jdbc:<em>subprotocol</em>:<em>subname</em>
     * @return a Driver that can connect to the URL 
     * @exception SQLException if a database-access error occurs.
     */
    public static Driver getDriver(String url) throws SQLException {
        println("DriverManager.getDriver(\"" + url + "\")");

        if (!initialized) {
            initialize();
        }

        // Figure out the current security context.
        Object currentSecurityContext = getSecurityContext();

        // 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 driver isn't part of the base system and doesn't come
            // from the same security context as the current caller, skip it.
            if (di.securityContext != null && 
                        di.securityContext != currentSecurityContext) {
                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");
    }


    /**
     * A newly loaded driver class should call registerDriver to make itself
     * known to the DriverManager.
     *
     * @param driver the new JDBC Driver 
     * @exception SQLException if a database-access error occurs.
     */