用字节码创建注释，但是我的代码找不到注释

Question

Currently I'm trying to generate my classes for my Tests via this:

AnnotationDescription entity = AnnotationDescription.Builder.ofType(Entity.class) //
    .build();

AnnotationDescription table = AnnotationDescription.Builder.ofType(Table.class) //
    .define("name", "FIRST_TABLE") //
    .build();

// @Column ( name = "X1", length = 20 )
AnnotationDescription nameAnnotationColumn = AnnotationDescription.Builder.ofType(Column.class) //
    .define("name", "X1") //
    .define("length", 20) //
    .build();

// @Column ( name = "X1", length = 20 )
AnnotationDescription nameAnnotationKeyColumn = AnnotationDescription.Builder.ofType(Column.class) //
    .define("name", "ADR_EXTERN_KEY") //
    .define("precision", 15) //
    .build();
Class<? extends Serializable> subclass = new ByteBuddy().subclass(Serializable.class) //
    .annotateType(entity, table) //
    .defineField("name", String.class, Visibility.PRIVATE).annotateField(nameAnnotationColumn) //
    .defineMethod("getName", String.class, Visibility.PUBLIC).intercept(FieldAccessor.ofField("name")) //
    .defineField("key", BigDecimal.class, Visibility.PRIVATE).annotateField(nameAnnotationKeyColumn) //
    .defineMethod("getKey", BigDecimal.class, Visibility.PUBLIC).intercept(FieldAccessor.ofField("key")) //
    .make() //
    .load(getClass().getClassLoader()) //
    .getLoaded();

But my own code is trying to identify a class which should have an annotation like @Entity and @Table(name = "XXX") . So the call to .annotatypeType(..) seemed to be either doing something I don't understand or I just create the annotations in a wrong way..

The code which tries to identify if the classes contain the @Entity and @Table annotation is in general like this:

public class X {
  private Class<? extends Serializable> givenClass;

  ...

if (hasAnnotation(this.givenClass.getClass().getAnnotations(), Entity.class)) {
 ....
}

where the method looks like this:

  private boolean hasAnnotation(Annotation[] annotations, Object annotationToBeExistent) {

    boolean result = false;
    for (int i = 0; i < annotations.length; i++) {
      if (annotations[i].annotationType().equals(annotationToBeExistent)) {
        result = true;
      }
    }
    return result;

If I create a class manually and implement is as usual the code finds the annotations...So I think my mistake must be somewhere in using byte-buddy ?

Update :

After thinking about it and the comment I found out that my creation was wrong it must look like this instead:

Serializable subclass = new ByteBuddy().subclass(Object.class) //
    .implement(Serializable.class)
    .annotateType(entity, table) //

But my code will not see the created annotations?

Update 2:

So after your comments/suggestions (which helped a lot; Thanks for the support) I have drilled down my problem to the following code snippet: I assume my usage of AnnotationDescription or creating the annotation is not correct cause the assert will result in false .

AnnotationDescription entity = AnnotationDescription.Builder.ofType(Entity.class) //
    .build();

Serializable subclass = new ByteBuddy().subclass(Object.class) //
    .implement(Serializable.class)
    .annotateType(entity) //
    .make() //
    .load(this.getClass().getClassLoader()) //
    .getLoaded();

assertThat(subclass.getClass().isAnnotationPresent(Entity.class)).isTrue();

Answer 1

Your API use is correct and I could even validate the working by invoking:

subclass.isAnnotationPresent(Entity.class)

on your resulting class. I assume that there is a problem in your scanning logic. Some tools scan classes by introspecting class files from jars directly, maybe this is the reason that you cannot locate the class?

As for your update, are you expecting for Byte Buddy to return an instance? Byte Buddy only generates classes and Class types implement the Serializable interface which is why your code compiles to begin with:

AnnotationDescription entity = AnnotationDescription.Builder
    .ofType(Entity.class)
    .build();

Class<?> subclass = new ByteBuddy().subclass(Object.class)
  .implement(Serializable.class)
  .annotateType(entity)
  .make()
  .load(this.getClass().getClassLoader())
  .getLoaded();

Now, the resulting class should carry your expected annotation. You can use reflection to create an instance that implements the Serializable interface.