Java Tutorial/Reflection/ClassPath

Get the path from where a class is loaded

public class Main {
  public static void main(String[] args) {
    Main csl = new Main();
    csl.getCodeSourceLocation();
  }
  private void getCodeSourceLocation() {
    System.out.println("Code source location: "
        + getClass().getProtectionDomain().getCodeSource().getLocation());
  }
}

Loading a Class That Is Not on the Classpath

A URLClassLoader can be used to load classes in any directory.
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file = new File("c:\\");
    URL url = file.toURI().toURL(); 
    URL[] urls = new URL[] { url };
    ClassLoader cl = new URLClassLoader(urls);
    Class cls = cl.loadClass("com.mycompany.MyClass");
  }
}

Load the class source location from Class.getResource()

public class Main {
  public static void main(String args[]) {
    Class theClass = Main.class;
    java.net.URL u = theClass.getResource("");
    System.out.println("This class (FromWhere) is located at : " + u);
  }
}

Obtain from where a Class is loaded

public class Main {
  public static void main(String args[]) {
    Main m = new Main();
    System.out.println(m.getClass().getName() + " is loaded from "
        + m.getClass().getProtectionDomain().getCodeSource().getLocation());
  }
}

Returns a reference to a file with the specified name that is located somewhere on the classpath.

/* 
 * JCommon : a free general purpose class library for the Java(tm) platform
 * 
 *
 * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
 * 
 * Project Info:  http://www.jfree.org/jcommon/index.html
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library 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 Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 * 
 * ------------------
 * FileUtilities.java
 * ------------------
 * (C) Copyright 2000-2004, by Object Refinery Limited.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   -;
 *
 * $Id: FileUtilities.java,v 1.5 2005/10/18 13:16:02 mungady Exp $
 *
 * Changes (from 5-Nov-2001)
 * -------------------------
 * 05-Nov-2001 : Changed package to com.jrefinery.io.* (DG);
 * 04-Mar-2002 : Renamed Files.java --> FileUtilities.java (DG);
 * 10-Oct-2002 : Fixed errors reported by Checkstyle (DG);
 *
 */
import java.io.File;
import java.util.StringTokenizer;
/**
 * A class containing useful utility methods relating to files.
 * 
 * @author David Gilbert
 */
public class FileUtilities {
  /**
   * Returns a reference to a file with the specified name that is located
   * somewhere on the classpath. The code for this method is an adaptation of
   * code supplied by Dave Postill.
   * 
   * @param name
   *          the filename.
   * 
   * @return a reference to a file or <code>null</code> if no file could be
   *         found.
   */
  public static File findFileOnClassPath(final String name) {
    final String classpath = System.getProperty("java.class.path");
    final String pathSeparator = System.getProperty("path.separator");
    final StringTokenizer tokenizer = new StringTokenizer(classpath, pathSeparator);
    while (tokenizer.hasMoreTokens()) {
      final String pathElement = tokenizer.nextToken();
      final File directoryOrJar = new File(pathElement);
      final File absoluteDirectoryOrJar = directoryOrJar.getAbsoluteFile();
      if (absoluteDirectoryOrJar.isFile()) {
        final File target = new File(absoluteDirectoryOrJar.getParent(), name);
        if (target.exists()) {
          return target;
        }
      } else {
        final File target = new File(directoryOrJar, name);
        if (target.exists()) {
          return target;
        }
      }
    }
    return null;
  }
}