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URLClassLoader: Modify Classpath At Runtime Java code example - Click here to copy ->>>

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The system classloader (ClassLoader.getSystemClassLoader()) is a subclass of URLClassLoader.

It can be casted into a URLClassLoader and used as one.



Code:

 
import java.io.IOException;
import java.io.File;
import java.net.URLClassLoader;
import java.net.URL;
import java.lang.reflect.Method;

public class ClassPathHacker {

   private static final Class[] parameters = new Class[]{URL.class};

   public static void addFile(String s) throws IOException {
      File f = new File(s);
      addFile(f);
   }//end method

   public static void addFile(File f) throws IOException {
      addURL(f.toURL());
   }//end method


   public static void addURL(URL u) throws IOException {

      URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
      Class sysclass = URLClassLoader.class;

      try {
         Method method = sysclass.getDeclaredMethod("addURL", parameters);
         method.setAccessible(true);
         method.invoke(sysloader, new Object[]{u});
      } catch (Throwable t) {
         t.printStackTrace();
         throw new IOException("Error, could not add URL to system classloader");
      }//end try catch

   }//end method

}//end class

 
 



References.

The list of classes which were used on this page you can find below. The links to Java API contain official SUN documentation about all used classes.

  java.net.URLClassLoader

  java.lang.Class

  java.io.IOException

  java.io.File

  java.net.URL

  java.lang.reflect.Method

  java.lang.Object

  java.lang.Throwable

  java.lang.Error




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