如何通过反射将字段值设置为纯对象

Question

I have a model class:

public class Model {

@KeyDefinition("name")
private String mName;

@KeyDefinition("age")
private int mAge;

public Model(){

}

And I have a List<Object> (Values) & a List<String> (Keys) that I handle through the map method:

public <T> T map(Class<T> cls){
    T instance;
    try {
        instance = cls.newInstance();
        for(Field field: cls.getDeclaredFields()){
            if(field.isAnnotationPresent(KeyDefinition.class)){
                KeyDefinition annotation = field.getAnnotation(KeyDefinition.class);
                for(int i = 0; i < mKeys.size(); i++){
                    if(annotation.value().equals(mKeys.get(i))){
                        field.setAccessible(true);
                        field.set(instance, mValues.get(i));
                    }
                }
            }
        }
    } catch (InstantiationException | IllegalAccessException e) {
        System.out.println(e.getMessage());
        return null;
    }
    return instance;
}

So if the value of the annotations is equals to a "Key" item from a list, then I grab the Object in the corresponding position and set the field's value to that.

But, when I reaches the mAge field I get the following message:

java.lang.IllegalArgumentException: Can not set int field Model.mAge to java.lang.String
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
at sun.reflect.UnsafeIntegerFieldAccessorImpl.set(UnsafeIntegerFieldAccessorImpl.java:98)

What I have possibly done wrong?

Answer 1

The error is pretty clear. Age is an int and you're trying to assign an Object to it through reflection. It's unsafe because the Object could be anything. You'll either need to a) determine the field type in your loop and convert Objects to whatever type accordingly, or b) give yourself a setter that can accept an Object, and go through setters rather than fields, or c) make the age field be a generic Object, which of course is not ideal.

Another strategy you could use is to make some object to whatever converter class and specify it as a parameter to your annotation, then use that to convert.

Sorry about lack of examples, on phone.