Friday, February 24, 2006
How to load subclass(es) from your jar file Mr. Endy Muhardin found problems in finding and loading classes when developing his opensource application. Hope this code will help him. Ganbatte Mas Endy!!Here is a simple code to illustrate how to load one or more subclass(es) from a jar file.
/*
* Created on Feb 24, 2006
*
*/
package com.monn;
import java.io.File;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import javax.swing.JFileChooser;
import javax.swing.JOptionPane;
/**
* @author Monang Setyawan
*
*/
public class Executor {
public static void main(String[] args) throws Exception {
new Executor().run();
System.exit(0);
}
public void run() throws Exception {
JFileChooser chooser = new JFileChooser();
if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
String parent;
if ((parent = JOptionPane.showInputDialog(null,
"superclass/interface name")) != null) {
File file = chooser.getSelectedFile();
URL jarUrl = new URL("jar:file:" + file.getAbsolutePath()
+ "!/");
JarFile jarFile = ((JarURLConnection) jarUrl.openConnection())
.getJarFile();
URL[] urls = { file.toURL() };
URLClassLoader loader = URLClassLoader.newInstance(urls, Thread
.currentThread().getContextClassLoader());
List nameList = getClassNames(jarFile);
for (Iterator iter = nameList.iterator(); iter.hasNext();) {
String classname = (String) iter.next();
Class clazz = loader.loadClass(classname);
if (Class.forName(parent).isAssignableFrom(clazz)) {
// you've got your class
System.out.println(clazz);
}
}
}
}
}
private List getClassNames(JarFile jarFile) {
List nameList = new ArrayList();
for (Enumeration enum = jarFile.entries(); enum.hasMoreElements();) {
JarEntry entry = (JarEntry) enum.nextElement();
String entryName = entry.getName();
if (entryName.endsWith(".class")) {
int startPos = entryName.lastIndexOf('.');
String shortName = entryName.substring(0, startPos);
shortName = shortName.replace('/', '.').replace('\\', '.');
nameList.add(shortName);
}
}
return nameList;
}
}
For simple test, you can select any JDBC driver jar file and type in "java.sql.Connection". My code above will try to find any implementations of Connection interface in your jar file.
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