Carsten Jäger [https://community.jboss.org/people/aumaster] created the discussion "Duplicate class definition error on CtClass.toClass() call" To view the discussion, visit: https://community.jboss.org/message/809164#809164 -------------------------------------------------------------- I'm trying to reflect annotation changes to classes. When i call the CtClass.toCalls method i always getting following error: *javassist.CannotCompileException: by java.lang.LinkageError: loader (instance of  sun/misc/Launcher$AppClassLoader): attempted  duplicate class definition for name: "ReflectionTest"* Googl'ing for a solution, told me to provide an *own ClassLoader* when calling the toClass() method. But i found no sample how to implement it... This is my Testcase: *1. The class to modify:* * * import javax.persistence.Table; *@Table(name="xyz")* public class ReflectionTest { } *2. The test class:* import java.util.ArrayList; import java.util.Collection; import javassist.ClassPool; import javassist.CtClass; import javassist.bytecode.AnnotationsAttribute; import javassist.bytecode.ConstPool; import javassist.bytecode.annotation.Annotation; import javassist.bytecode.annotation.StringMemberValue; import javax.persistence.Table; public class ReflectionSample {     public static void main(final String[] args) { *        /** *         * It's no solution to provide just the class names as a string,* *         * what will only work, if no application part accessed the classes already.* *         */*         final Collection<Class<?>> classes = new ArrayList<Class<?>>();         classes.add(ReflectionTest.class);         doReflection(classes);         final ReflectionTest test = new ReflectionTest();         final Table table = test.getClass().getAnnotation(Table.class);         System.out.println("name  : " + table.name());         System.out.println("schema: " + table.schema()); // Expecting: "TestSchema"     }     private static void doReflection(final Collection<Class<?>> classes) {         final ClassPool classPool = ClassPool.getDefault();         for (final Class<?> clazz : classes) {             try {                 final CtClass ctClass = classPool.get(clazz.getName());                 final ConstPool constPool = ctClass.getClassFile().getConstPool();                 final AnnotationsAttribute attribute = new AnnotationsAttribute(constPool, AnnotationsAttribute.visibleTag);                 final Table table = (Table) ctClass.getAnnotation(Table.class);                 final Annotation tableAnnotation = new Annotation("javax.persistence.Table", constPool);                 tableAnnotation.addMemberValue("name", new StringMemberValue(table.name(), constPool));                 tableAnnotation.addMemberValue("schema", new StringMemberValue("TestSchema", constPool));                 attribute.addAnnotation(tableAnnotation);                 ctClass.getClassFile().addAttribute(attribute);                 // This throws a java.lang.LinkageError ... attempted  duplicate class definition for name: "ReflectionTest"!                 ctClass.toClass();             } catch (Exception e) {                 e.printStackTrace();             }         }     } } *Any help is appreciated!* *Tia, Carsten* *P.S.: See attached ZIP file for the complete sample. * * * -------------------------------------------------------------- Reply to this message by going to Community [https://community.jboss.org/message/809164#809164] Start a new discussion in Javassist at Community [https://community.jboss.org/choose-container!input.jspa?contentType=1&...]