Add a jar file to Java load path at run time

mikewilsonuk (Mike Wilson) — Fri, 23 Feb 2007 15:24:18 GMT

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 ();

        }

    }

}

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Add a jar file to Java load path at run time