Question

I want to write my own validator and code generator for my beans. I define annotations and annotate my fields with them. When I validate them:

public boolean validate(Object obj) {
    Class clazz = obj.getClass();
    for (Field field : clazz.getDeclaredFields()) {
        for (Annotation annotation : field.getAnnotations()) {
            ...//What to do here
        }
    }
    return false;
}

i.e. my annotation is @NotEmpty

Should I go like if else if else ... or is there any other short way for it(and what to use to compare is that the annotation that I look i.e. @NotNull -> with annotation.equals(“NotNull”))? I mean how it can be implemented. On the other hand project Lombok has an annotation like that:

@Getter @Setter

How to generate getter and setters dynamically (or before compiling) for my classes(I want to implement it just with Java without any other libraries)?

Answer 1

I think you’d better search for the annotations you need rather that looping through all annotations. You can see if a annotation is present like this:

field.isAnnotationPresent(NotEmpty.class)

And to get the annotation and check it’s elements you can use:

Annotation notEmpty = field.getAnnotation(NotEmpty.class)

To modify your classes at runtime I think this is what you’re looking for. Here you can find a tutorial for ASM.