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import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import org.apache.bcel.Constants;
import org.apache.bcel.classfile.ClassParser;
import org.apache.bcel.classfile.JavaClass;
....

public class Transf implements ClassFileTransformer {
	public byte[] transform(ClassLoader loader, 
                                String className, 
                                Class redefiningClass, 
                                ProtectionDomain domain, 
                                byte[] bytes) throws IllegalClassFormatException {
                try {
                    ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes),className);
                    JavaClass clazz = parser.parse();
                    clazz.setAccessFlags(clazz.getAccessFlags() & (~Constants.ACC_FINAL ));
                    bytes = clazz.getBytes();
                    System.out.println("Transformed Class: " + className);
                } catch (ClassFormatError ex) {
                    ex.printStackTrace();
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            return bytes;
	}
}

To initialize the class patching agent it is necessary to create premain class:

public class SimpleMain {
	public static void premain(String agentArguments, Instrumentation instrumentation) {	
		instrumentation.addTransformer(new Transf());
	}	
}

 
Manifest-Version: 1.0 
Premain-Class: mypackage.SimpleMain

java -javaagent:classpatching.jar ...