Add a jar file to Java load path at run time
Sometimes it is necessary to amend the class load path at run time. For example, dynamically adding jar files containing user-configurable JDBC data sources. The way this is done is truly monstrous -- the URL Path format was only revealed when a colleague looked into the Java library sources.
import java.net.URL; import java.io.IOException; import java.net.URLClassLoader; import java.net.MalformedURLException; public class JarFileLoader extends URLClassLoader { public JarFileLoader (URL[] urls) { super (urls); } public void addFile (String path) throws MalformedURLException { String urlPath = "jar:file://" + path + "!/"; addURL (new URL (urlPath)); } public static void main (String args []) { try { System.out.println ("First attempt..."); Class.forName ("org.gjt.mm.mysql.Driver"); } catch (Exception ex) { System.out.println ("Failed."); } try { URL urls [] = {}; JarFileLoader cl = new JarFileLoader (urls); cl.addFile ("/opt/mysql-connector-java-5.0.4/mysql-connector-java-5.0.4-bin.jar"); System.out.println ("Second attempt..."); cl.loadClass ("org.gjt.mm.mysql.Driver"); System.out.println ("Success!"); } catch (Exception ex) { System.out.println ("Failed."); ex.printStackTrace (); } } }
