Adding files to java classpath at runtime [duplicate]

You can only add folders or jar files to a class loader. So if you have a single class file, you need to put it into the appropriate folder structure first.

Here is a rather ugly hack that adds to the SystemClassLoader at runtime:

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

The reflection is necessary to access the protected method addURL. This could fail if there is a SecurityManager.

Try this one on for size.

private static void addSoftwareLibrary(File file) throws Exception {    Method method = URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{URL.class});    method.setAccessible(true);    method.invoke(ClassLoader.getSystemClassLoader(), new Object[]{file.toURI().toURL()});}

This edits the system class loader to include the given library jar. It is pretty ugly, but it works.

The way I have done this is by using my own class loader

URLClassLoader urlClassLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();DynamicURLClassLoader dynalLoader = new DynamicURLClassLoader(urlClassLoader);

And create the following class:

public class DynamicURLClassLoader extends URLClassLoader {    public DynamicURLClassLoader(URLClassLoader classLoader) {        super(classLoader.getURLs());    }    @Override    public void addURL(URL url) {        super.addURL(url);    }}

Works without any reflection