URLClassLOader unable to load classes from jar dynamically

Question

 URLClassLoader child; try { child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, Test2.class.getClassLoader()); child.loadClass("com.bla.bla.StringUtilService"); } catch (MalformedURLException | ClassNotFoundException ex) { ex.printStackTrace(); }

I am getting ClassNotFoundException in loadClass.

I have tried several variants of the code such as

URL[] urls = { new URL("jar:file:" + "E:\\Works\\Workspace\\JUnit_Proj\\client.jar"+"!/") }; URLClassLoader cl = URLClassLoader.newInstance(urls);

But all results into ClassNotFoundException!

I have tried debugging in Eclipse, but the class loader instance is unable to load classes from the jar. The classes Vector is empty.

What is the type of myJar?

Henry
– Henry

2014-11-01 07:42:49 +00:00
Commented Nov 1, 2014 at 7:42 — Henry
– Henry, Commented Nov 1, 2014 at 7:42
@Henry : java.io.File. Tried with JarFile as well.

javaCurious
– javaCurious

2014-11-01 10:17:33 +00:00
Commented Nov 1, 2014 at 10:17 — javaCurious
– javaCurious, Commented Nov 1, 2014 at 10:17

javaCurious · Accepted Answer · 2014-11-04 14:13:33Z

Succeeded using different costructor of URLClassLoader.

  try { File jarFile = new File("D:\\Workspace\\Test\\Test.jar"); URLClassLoader loader = new URLClassLoader(new URL[]{jarFile.toURI().toURL()}); Class.forName("com.bla.bla.HelloWorld", true, loader); System.out.println("Success"); loader.close(); } catch (MalformedURLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); }

Community · Accepted Answer · 2017-05-23 11:51:11Z

The class is a direct child of the dir in the url, so you need no package.

Try this without the package. Like this:

URLClassLoader child; try { child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, Test2.class.getClassLoader()); child.loadClass("StringUtilService"); } catch (MalformedURLException | ClassNotFoundException ex) { ex.printStackTrace(); }

Also, try like this:

URLClassLoader child; try { child = new URLClassLoader(new URL[]{myJar.toURI().toURL()}, getClass().class.getClassLoader()); child.loadClass("StringUtilService"); } catch (MalformedURLException | ClassNotFoundException ex) { ex.printStackTrace(); }

Solution from: ClassNotFoundException while loading a class from file with URLClassLoader

Anyone has successfully loaded classes from jars dynamically?

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