Why I can't access to field class using reflection?

Question

I use java spring for my project. I try to access the property and set it with a specific value using the reflection.

I try to access the name property of User class:

@Data
public class User {
    @Id
    private String id;
    private String name;
    private String phone;
    private String email;
}

Here how I try to access the name field:

User newUser = userRepository.get(id); 
User user = accessProp(newUser, User.class, "name", "John");


public <D> D accessProp(Class<D> dest, String fieldName, Object value ){
    Field filed = null;
    var cls = AdminUser.class;

    filed = cls.getField(fieldName);
    filed.set(dest, value);

    return dest;
}

But on this row:

 filed = cls.getField(fieldName);

I get this error:

 java.lang.NoSuchFieldException: name

My question is why "name" field not found?

_why_, though? Do you know what `@Data` does? You already have a `public` getter in the class — Eugene, Jul 24 '21 at 03:17

score 4 · Accepted Answer · answered Jul 24 '21 at 02:52

4

My question is why is the "name" field not found?

The getField method does not return private fields. You need to use getDeclaredField to get a private field. But getDeclaredField only returns fields for the target class.

So to find and update a private field (in the given class) you need to do something like this:

Field field = User.class.getDeclaredField("name");
field.setAccessible(true);
field.set(userObject, value);

(Notice that you also need to use setAccessible to allow access to a private field.)

If you wanted to set a named private field in some superclass of a given class, you would need to use getSuperclass() to traverse the superclass chain until you found the Class that has the field you are looking for.

answered Jul 24 '21 at 02:52

Stephen C

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Thank you for the post. In the class, I have @Data annotation, I should create public Set props, any idea how can I use it to access and modify fields value? – Michael Jul 24 '21 at 03:24
1

@Michael Use `getMethod("setName", String.class)`, then call `method.invoke("Foo")`. Since the method is public, you don't need to use `getDeclaredMethod` and you don't need to call `setAccessible`. – Andreas Jul 24 '21 at 03:28
@Andreas, thanks for this great comment. Can you create a post, please? – Michael Jul 24 '21 at 04:26
1

@Michael - what you have done is asked a >different< question in a comment. Putting an answer to that comment that into an Answer to your original Question wouldn't make much sense. I expect that's why Andreas didn't do that in the first place. – Stephen C Jul 24 '21 at 04:33

Why I can't access to field class using reflection?

1 Answers1