How do I get all Record fields and its values via reflection in Java 17?

Question

I had a class:

class A {
   public final Integer orgId;
}

I replaced it with the record in Java 17:

record A (Integer orgId) {
}

Also, I had a code that did a validation via reflection that is working with the regular class, but doesn't work with the Records:

Field[] fields = obj.getClass().getFields(); //getting empty array here for the record
for (Field field : fields) {
}

What would be the correct way to get the Record object fields and its values via reflection in Java 17?

Arvind Kumar Avinash · Accepted Answer · 2021-10-13T12:32:42.143

You can use the following method:

RecordComponent[] getRecordComponents()

You can retrieve name, type, generic type, annotations, and its accessor method from RecordComponent.

Point.java:

record Point(int x, int y) { }

RecordDemo.java:

import java.lang.reflect.RecordComponent;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

public class RecordDemo {
    public static void main(String args[]) throws InvocationTargetException, IllegalAccessException {
        Point point = new Point(10,20);
        RecordComponent[] rc = Point.class.getRecordComponents();
        System.out.println(rc[0].getAccessor().invoke(point));
    }
}

Output:

Alternatively,

import java.lang.reflect.RecordComponent;
import java.lang.reflect.Field;

public class RecordDemo {
    public static void main(String args[]) 
            throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException {
        Point point = new Point(10, 20);
        RecordComponent[] rc = Point.class.getRecordComponents();      
        Field field = Point.class.getDeclaredField(rc[0].getAccessor().getName());  
        field.setAccessible(true); 
        System.out.println(field.get(point));
    }
}

score 1 · Answer 2 · answered Oct 13 '21 at 10:58

1

Your class and record aren't equivalent: records have private fields.

Class#getFields() returns public fields only.

You could use Class#getDeclaredFields() instead.

answered Oct 13 '21 at 10:58

sp00m

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getDeclaredFields() doesn't work. Returns empty array. – Dmitriy Dumanskiy Oct 13 '21 at 11:08
@DmitriyDumanskiy This is weird, I just tried locally with `record R(int i) {}`, I do get `[private final int R.i]` when calling `R.class.getDeclaredFields()`. I'm running Temurin's OpenJDK 17 on macOS. Which JDK are you running? – sp00m Oct 13 '21 at 13:28
2

`getDeclaredFields()` does work. – Holger Oct 13 '21 at 15:46
@sp00m you're right. I misplaced with getFields() method. – Dmitriy Dumanskiy Oct 13 '21 at 17:10

How do I get all Record fields and its values via reflection in Java 17?

2 Answers2