How to load JAR files dynamically at Runtime?

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The reason it’s hard is security. Classloaders are meant to be immutable; you shouldn’t be able to willy-nilly add classes to it at runtime. I’m actually very surprised that works with the system classloader. Here’s how you do it making your own child classloader:

URLClassLoader child = new URLClassLoader(
        new URL[] {myJar.toURI().toURL()},
        this.getClass().getClassLoader()
);
Class classToLoad = Class.forName("com.MyClass", true, child);
Method method = classToLoad.getDeclaredMethod("myMethod");
Object instance = classToLoad.newInstance();
Object result = method.invoke(instance);

Painful, but there it is.

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