Java Tutorial/Reflection/ClassPath
Содержание
Get the path from where a class is loaded
<source lang="java">
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()); }
}</source>
Loading a Class That Is Not on the Classpath
<source lang="java">
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"); }
}</source>
Load the class source location from Class.getResource()
<source lang="java">
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); }
}</source>
Obtain from where a Class is loaded
<source lang="java">
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()); }
}</source>
Returns a reference to a file with the specified name that is located somewhere on the classpath.
<source lang="java">
/*
* 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 null
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;
}
}</source>