How to add an external jar file to the classpath dynamically at runtime?

Question

I want to add a JAR file to my project's classpath dynamically using Java code. If it is possible, I want to use external jar files and load their classes, and then execute them as beans later (Spring Framework).

score 16 · Accepted Answer · edited May 23 '17 at 12:34

16

URLClassLoader child = new URLClassLoader (myJar.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);

Source: https://stackoverflow.com/a/60775/1360074

edited May 23 '17 at 12:34

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answered Mar 04 '13 at 15:30

Nikolay Kuznetsov

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You shouldn't really use `Class#newInstance()` because it can introduce an undeclared checked exception http://docs.oracle.com/javase/tutorial/reflect/member/ctorTrouble.html it's better to use `Class#getConstructor()#newInstance()` – Philippe Marschall Mar 04 '13 at 15:41
Thank NiKolay Kusznetov , I found the Answer int Source discussion :) – EL Kamel Mar 04 '13 at 15:50

Rahul · Answer 2 · 2014-03-18T08:55:10.120

You can try something like this, but it requires you to know, where exactly your JARs are located.

URLClassLoader cl = URLClassLoader.newInstance(new URL[] {myJarFiles});
Class myClass = cl.loadClass("com.mycomp.proj.myclass");
Method printMeMethod = myClass.getMethod("printMe", new Class[] {String.class, String.class});
Object myClassObj = myClass.newInstance();
Object response = printMeMethod.invoke(myClassObj, "String1", "String2");

How to add an external jar file to the classpath dynamically at runtime?

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