I'm using Javassist(Java 1.7) to add an annotation to the class ClassA, but i get the exception. What am i doing wrong? The code I tried looks like this:
ClassA.java
public class ClassA
{
}
add method
public static <T> Class<T> addXmlRootAnnotationDynamicly(Class<T> declaredTyp) throws NotFoundException, CannotCompileException, InstantiationException, IllegalAccessException
{
//pool creation
ClassPool pool = ClassPool.getDefault();
//extracting the class
CtClass cc = pool.getCtClass(declaredTyp.getCanonicalName());
// create the annotation
ClassFile ccFile = cc.getClassFile();
ConstPool constpool = ccFile.getConstPool();
AnnotationsAttribute attr = new AnnotationsAttribute(constpool, AnnotationsAttribute.visibleTag);
Annotation annot = new Annotation("javax.xml.bind.annotation.XmlRootElement", constpool);
attr.addAnnotation(annot);
// add the annotation to the class
cc.getClassFile().addAttribute(attr);
// transform the ctClass to java class
Class<T> dynamiqueBeanClass = cc.toClass();
//instanciating the updated class
// T sayHelloBean = dynamiqueBeanClass.newInstance();
return dynamiqueBeanClass;
}
call
Class<ClassA> addXmlRootAnnotationDynamicly = addXmlRootAnnotationDynamicly(ClassA.class);
Exception
javassist.CannotCompileException: by java.lang.LinkageError: loader (instance of sun/misc/Launcher$AppClassLoader): attempted duplicate class definition for name: "de/it_p/pvlight/share/util/ClassA" at javassist.ClassPool.toClass(ClassPool.java:1099) at javassist.ClassPool.toClass(ClassPool.java:1042) at javassist.ClassPool.toClass(ClassPool.java:1000) at javassist.CtClass.toClass(CtClass.java:1224) at de.it_p.pvlight.share.util.JAXBUtil.addXmlRootAnnotationDynamicly(JAXBUtil.java:107) at de.it_p.pvlight.share.util.JAXBUtilTest.addXmlRootAnnotationDynamicly(JAXBUtilTest.java:60) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.lang.reflect.Method.invoke(Method.java:606) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.lang.reflect.Method.invoke(Method.java:606) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) Caused by: java.lang.LinkageError: loader (instance of sun/misc/Launcher$AppClassLoader): attempted duplicate class definition for name: "de/it_p/pvlight/share/util/ClassA" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.lang.ClassLoader.defineClass(ClassLoader.java:643) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.lang.reflect.Method.invoke(Method.java:606) at javassist.ClassPool.toClass2(ClassPool.java:1112) at javassist.ClassPool.toClass(ClassPool.java:1093) ... 15 more
The root of your problem can be found in your stack trace:
attempted duplicate class definition for name: "de/it_p/pvlight/share/util/ClassA"
Your addXmlRootAnnotationDynamicly
method takes a loaded class and redefines this very same class without changing its name. After this redefinition, you attempt to load the altered class one more time. This is however not possible in Java where any ClassLoader
can only load a class of a given name one single time.
For this reason, the pool.getCtClass
method takes a String
instead of a loaded Class
and works with CtClass
es which are used to describe unloaded Class
es. To overcome your problem, you have different choices:
addXmlRootAnnotationDynamicly(String)
and deliver de.it_p.pvlight.share.util.ClassA
as the argument. Make sure that this class is not loaded before you transform it, anywhere in your code. You should therefore run the transformation at your application's startup to make sure that the class is not accidentally loaded before the transformation. Your altered Class
is then loaded on cc.toClass()
.ClassLoader
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