javassist not injecting annotation at existing field - jaxb

Question

I'm trying to inject JAXB annotation at runtime using Javassist. I have written following code:
public class AssistAnnotationInjector {
public static void addAnnotationRunTime(String className, String fieldName) throws NotFoundException, CannotCompileException, IOException, ClassNotFoundException{
CtClass ctClass = ClassPool.getDefault().get(className);
ClassFile ccFile = ctClass.getClassFile();
ConstPool constPool = ccFile.getConstPool();
AnnotationsAttribute attr = new AnnotationsAttribute(constPool, AnnotationsAttribute.visibleTag);
Annotation annot = new Annotation("javax.xml.bind.annotation.XmlTransient",constPool);
attr.addAnnotation(annot);
CtField field = ctClass.getDeclaredField(fieldName);
field.getFieldInfo().addAttribute(attr);
System.out.println(field.getAnnotation(XmlTransient.class));
ccFile.setVersionToJava5();
ctClass.writeFile();
}
public static void main (String args[]) throws CannotCompileException, NotFoundException, IOException, SecurityException, NoSuchMethodException, ClassNotFoundException, JAXBException, NoSuchFieldException{
Person<Student> p = new Person<Student>();
p.setName("XYZ");
Student s = new Student();
s.setName("ABC");
s.setId("239423");
p.setPayload(s);
addAnnotationRunTime("RuntimeAnnotation.Person", "name");
Field f = p.getClass().getDeclaredField("name");
System.out.println(f.getAnnotation(XmlTransient.class));
JAXBContext context = JAXBContext.newInstance(p.getClass());
Marshaller mr = context.createMarshaller();
mr.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
mr.marshal(p, System.out);
}
}
And Person.java class is:
#XmlRootElement(name="Person")
#XmlAccessorType(XmlAccessType.FIELD)
#XmlSeeAlso({Student.class})
public class Person <T>{
private T payload;
private String name;
public void setPayload(T payload){
this.payload = payload;
}
public T getPayload(){
return payload;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return name;
}
}
In AssistAnnotationInjector.java, I am trying to add XmlTransient annotation to 'name' field. But the name field is still coming in marshalling output. Why is it so?
PS: marshal output is :
#javax.xml.bind.annotation.XmlTransient
null
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Person>
<payload xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="student">
<name>ABC</name>
<id>239423</id>
</payload>
**<name>XYZ</name>**
</Person>
name tag was not expected to present in output..

Answer 1

You basicaly have 2 options:
do the modification before you load the class. You can not use reflection in the normal way! One can try to use org.reflections with Maven plugin to pre-fetch classes. See here for more info.
use custom classloader to load the modified class. See here for more info.

Answer 2

After adding the attribute to the field you need to call ctClass.toClass() method,which freezes the class. After this you can check for the annotation.