CODEWITHSUNDEEP
javanetbeans-8
user5049374
user5049374

Reputation:

Java classpath and classloading

I need load a jar file in runtime in Java and I have this code but it not load any jar and I don't know how, somebody can tell me why? I have JVM 8 and NetBeans 8, the purpose is create a program that can load jar files as a plugins y for Windows.

package prueba.de.classpath;
import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

public class PruebaDeClasspath {

    public static void main(String[] args) {
        try {
            Class.forName("PluginNumeroUno");
        } catch (ClassNotFoundException e) {
            System.out.println("Not Found");
        }

        try {
            URLClassLoader classLoader = ((URLClassLoader) ClassLoader
                    .getSystemClassLoader());
            Method metodoAdd = URLClassLoader.class.getDeclaredMethod("addURL",
                    new Class[]{URL.class});
            metodoAdd.setAccessible(true);


            File file = new File("plugins/PrimerPlugins.jar");

            URL url = file.toURI().toURL();
            System.out.println(url.toURI().toURL());

            metodoAdd.invoke(classLoader, new Object[]{url});
        } catch (Exception e) {
            e.printStackTrace();
        }

        try {
            Class.forName("PluginNumeroUno");
            System.out.println("ok");
        } catch (ClassNotFoundException e) {
            System.out.println("Not Found");
        }

    }

}

Upvotes: 1

Views: 445

Answers (1)

diginoise
diginoise

Reputation: 7620

Try creating new class loader instead of casting the system classloader.

Remove this line:

URLClassLoader classLoader = ((URLClassLoader) ClassLoader.getSystemClassLoader());

and create the new loader and use it as below:

File file = new File("plugins/PrimerPlugins.jar");
URLClassLoader classLoader = new URLClassLoader(new URL[]{file.toURI().toURL()},    
    PruebaDeClasspath.class.getClassLoader());
Class.forName("prueba.de.classpath.PluginNumeroUno", true, classLoader); //fully qualified!

Please note that the class name to be loaded has to be fully qualified.

You also don't have to dynamically force addURL() to be public.

Upvotes: 1

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