Can not remove the modifier of final class - junit

Question

I want to remove final key word of 1 class. I'm writting Junit for this class and I call spy of Mockito to mock a method to return an expect values to cover all cases.
After using:
CtClass ctClazz = ClassPool.getDefault().get(Livre.class.getName());
ctClazz.setModifiers(ctClazz.getModifiers() & ~Modifier.FINAL);
ctClazz.writeFile();
The modifier of this class is 17 but I think it should be 1 (public).
And I got the error:
Caused by: java.lang.IllegalArgumentException: Cannot subclass final class class mediatheque.document.Livre
at net.sf.cglib.proxy.Enhancer.generateClass(Enhancer.java:446)
at net.sf.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:216)
at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377)
at net.sf.cglib.proxy.Enhancer.createClass(Enhancer.java:317)
at org.powermock.api.easymock.internal.signedsupport.SignedSupportingClassProxyFactory.createProxy(SignedSupportingClassProxyFactory.java:147)
at org.easymock.internal.MocksControl.createMock(MocksControl.java:40)
at org.easymock.classextension.internal.MocksClassControl.createMock(MocksClassControl.java:43)
at org.powermock.api.easymock.PowerMock.doMock(PowerMock.java:2076)
at org.powermock.api.easymock.PowerMock.createMock(PowerMock.java:79)
at org.powermock.api.easymock.PowerMock.createPartialMock(PowerMock.java:765)
at test.mediatheque.document.TestDocument.testRestituer_With_Exception3(TestDocument.java:379)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$2.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:217)
... 19 more
This final class extends from an abstract class.
Thanks for any help.

Answer 1

You cannot extend (subclass) a final class. If you really need to do so (whether for testing or because you really need to override a method in someone else's library), you'll have to 'fork' the class. Copy its contents into a new class (updating package declaration and class references), and remove the final designation there. Then, you can extend it to your heart's content. I've used this approach quite effectively recently with respect to Spring Security.