java.fedora.utilities.DriverShim Maven / Gradle / Ivy

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/*
 * -----------------------------------------------------------------------------
 *
 * License and Copyright: The contents of this file are subject to the
 * Apache License, Version 2.0 (the "License"); you may not use 
 * this file except in compliance with the License. You may obtain a copy of 
 * the License at 
 * http://www.fedora-commons.org/licenses.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
 * the specific language governing rights and limitations under the License.
 *
 * The entire file consists of original code.
 * Copyright © 2008 Fedora Commons, Inc.

 * 
Copyright © 2002-2007 The Rector and Visitors of the University of 
 * Virginia and Cornell University
 
 * All rights reserved.
 *
 * -----------------------------------------------------------------------------
 */
package fedora.utilities;

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.DriverPropertyInfo;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

/**
 * Allows one to load a JDBC driver at runtime.
 * java.sql.DriverManager will refuse to use a driver not loaded by the system 
 * ClassLoader. The workaround for this is to use a shim class that 
 * implements java.sql.Driver. This shim class will do nothing but call the 
 * methods of an instance of a JDBC driver that is loaded dynamically. This 
 * works because DriverShim is loaded by the system class loader, and 
 * DriverManager doesn't care that it invokes a class that wasn't.
 * 
 * Note that we must perform the registration on the instance ourselves.
 * 
 * See the utility method, loadAndRegister and the command-line test below.
 * 
 * Adapted from http://www.kfu.com/~nsayer/Java/dyn-jdbc.html
 */
public class DriverShim implements Driver {

	/** The JDBC driver we're wrapping. */
	private Driver _driver;

	/**
	 * Constructs a DriverShim over the given driver in order to make it look
	 * like it came from this classloader.
	 */
	public DriverShim(Driver d) {
		_driver = d;
	}

	/**
	 * Loads the driver from the given jar file and registers it with the driver
	 * manager.
	 */
	public static final void loadAndRegister(File driverJarFile,
			String driverClassName) throws Exception {
		loadAndRegister(new URL("jar:" + driverJarFile.toURI() + "!/"), driverClassName);
	}
	
	public static final void loadAndRegister(URL driverURL,
			String driverClassName) throws Exception {
		URLClassLoader urlCL = new URLClassLoader(new URL[] { driverURL });
		Driver driver = (Driver)Class.forName(driverClassName, true, urlCL).newInstance();
		DriverManager.registerDriver(new DriverShim(driver));
	}

	//
	// Driver implementation
	//

	/**
	 * {@inheritDoc}
	 */
	public boolean acceptsURL(String u) throws SQLException {
		return _driver.acceptsURL(u);
	}

	/**
	 * {@inheritDoc}
	 */
	public Connection connect(String u, Properties p) throws SQLException {
		return _driver.connect(u, p);
	}

	/**
	 * {@inheritDoc}
	 */
	public int getMajorVersion() {
		return _driver.getMajorVersion();
	}

	/**
	 * {@inheritDoc}
	 */
	public int getMinorVersion() {
		return _driver.getMinorVersion();
	}

	/**
	 * {@inheritDoc}
	 */
	public DriverPropertyInfo[] getPropertyInfo(String u, Properties p)
			throws SQLException {
		return _driver.getPropertyInfo(u, p);
	}

	/**
	 * {@inheritDoc}
	 */
	public boolean jdbcCompliant() {
		return _driver.jdbcCompliant();
	}

	/**
	 * Command-line test.
	 * 
	 * Dynamically loads the driver given at the command line, opens a
	 * connection, and get the row count of the given table to prove it worked.
	 * 
	 * Usage:
	 * 
	 * java -cp . DriverShim someDriver.jar org.SomeDriver jdbcURL name pwd tbl
	 */
	public static void main(String[] args) throws Exception {
		if (args.length == 6) {
			DriverShim.loadAndRegister(new File(args[0]), args[1]);
			Connection conn = DriverManager.getConnection(args[2], args[3],
					args[4]);
			String tbl = args[5];
			Statement st = conn.createStatement();
			ResultSet rs = st.executeQuery("SELECT COUNT(*) FROM " + tbl);
			rs.next();
			System.out.println("The " + tbl + " table has " + rs.getInt(1)
					+ " rows.");
			rs.close();
			st.close();
			conn.close();
		} else {
			System.out.println("Usage: java -cp . DriverShim someDriver.jar"
					+ " org.SomeDriver jdbcURL name pwd tbl");
			System.exit(1);
		}
	}
}