[jboss-user] [Javassist] - Duplicate class definition error on CtClass.toClass() call

[Carsten Jäger]

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

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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.
*
*
*
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