Retrieving the inherited attribute names/values using Java Reflection

Question

I've a Java object 'ChildObj' which is extended from 'ParentObj'. Now, if it is possible to retrieve all the attribute names and values of ChildObj, including the inherited attributes too, using Java reflection mechanism?

Class.getFields gives me the array of public attributes, and Class.getDeclaredFields gives me the array of all fields, but none of them includes the inherited fields list.

Is there any way to retrieve the inherited attributes also?

Answer 1

no, you need to write it yourself. It is a simple recursive method called on Class.getSuperClass():

public static List<Field> getAllFields(List<Field> fields, Class<?> type) {
    fields.addAll(Arrays.asList(type.getDeclaredFields()));

    if (type.getSuperclass() != null) {
        getAllFields(fields, type.getSuperclass());
    }

    return fields;
}

@Test
public void getLinkedListFields() {
    System.out.println(getAllFields(new LinkedList<Field>(), LinkedList.class));
}

Answer 2

    public static List<Field> getAllFields(Class<?> type) {
        List<Field> fields = new ArrayList<Field>();
        for (Class<?> c = type; c != null; c = c.getSuperclass()) {
            fields.addAll(Arrays.asList(c.getDeclaredFields()));
        }
        return fields;
    }

Answer 3

If instead you wanted to rely upon a library to accomplish this, Apache Commons Lang version 3.2+ provides FieldUtils.getAllFieldsList:

import java.lang.reflect.Field;
import java.util.AbstractCollection;
import java.util.AbstractList;
import java.util.AbstractSequentialList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

import org.apache.commons.lang3.reflect.FieldUtils;
import org.junit.Assert;
import org.junit.Test;

public class FieldUtilsTest {

    @Test
    public void testGetAllFieldsList() {

        // Get all fields in this class and all of its parents
        final List<Field> allFields = FieldUtils.getAllFieldsList(LinkedList.class);

        // Get the fields form each individual class in the type's hierarchy
        final List<Field> allFieldsClass = Arrays.asList(LinkedList.class.getFields());
        final List<Field> allFieldsParent = Arrays.asList(AbstractSequentialList.class.getFields());
        final List<Field> allFieldsParentsParent = Arrays.asList(AbstractList.class.getFields());
        final List<Field> allFieldsParentsParentsParent = Arrays.asList(AbstractCollection.class.getFields());

        // Test that `getAllFieldsList` did truly get all of the fields of the the class and all its parents 
        Assert.assertTrue(allFields.containsAll(allFieldsClass));
        Assert.assertTrue(allFields.containsAll(allFieldsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParentsParent));
    }
}

Answer 4

You need to call:

Class.getSuperclass().getDeclaredFields()

Recursing up the inheritance hierarchy as necessary.

Answer 5

Use Reflections library:

public Set<Field> getAllFields(Class<?> aClass) {
    return org.reflections.ReflectionUtils.getAllFields(aClass);
}

Answer 6

The recursive solutions are OK, the only small issue is that they return a superset of declared and inherited members. Note that getDeclaredFields() method returns also private methods. So given that you navigate the whole superclass hierarchy you will include all private fields declared in the superclasses, and those don't get inherited.

A simple filter with a Modifier.isPublic || Modifier.isProtected predicate would do:

import static java.lang.reflect.Modifier.isPublic;
import static java.lang.reflect.Modifier.isProtected;

(...)

List<Field> inheritableFields = new ArrayList<Field>();
for (Field field : type.getDeclaredFields()) {
    if (isProtected(field.getModifiers()) || isPublic(field.getModifiers())) {
       inheritableFields.add(field);
    }
}

Answer 7

private static void addDeclaredAndInheritedFields(Class<?> c, Collection<Field> fields) {
    fields.addAll(Arrays.asList(c.getDeclaredFields())); 
    Class<?> superClass = c.getSuperclass(); 
    if (superClass != null) { 
        addDeclaredAndInheritedFields(superClass, fields); 
    }       
}

Working version of "DidYouMeanThatTomHa..." solution above

Answer 8

You can try:

   Class parentClass = getClass().getSuperclass();
   if (parentClass != null) {
      parentClass.getDeclaredFields();
   }

Answer 9

Shorter and with less object instantiated ? ^^

private static Field[] getAllFields(Class<?> type) {
    if (type.getSuperclass() != null) {
        return (Field[]) ArrayUtils.addAll(getAllFields(type.getSuperclass()), type.getDeclaredFields());
    }
    return type.getDeclaredFields();
}

Answer 10

private static void addDeclaredAndInheritedFields(Class c, Collection<Field> fields) {
    fields.addAll(Arrays.asList(c.getDeclaredFields()));
    Class superClass = c.getSuperclass();
    if (superClass != null) {
        addDeclaredAndInheritedFields(superClass, fields);
    }
}

Answer 11

This is a rewording of the accepted answer by @user1079877. It might that a version which does not modify a parameter of the function and also uses some modern Java features.

public <T> Field[] getFields(final Class<T> type, final Field... fields) {
    final Field[] items = Stream.of(type.getDeclaredFields(), fields).flatMap(Stream::of).toArray(Field[]::new);
    if (type.getSuperclass() == null) {
        return items;
    } else {
        return getFields(type.getSuperclass(), items);
    }
}

This implementation also makes invocation a bit more concise:

var fields = getFields(MyType.class);

Answer 12

I recently saw this code from org.apache.commons.lang3.reflect.FieldUtils

public static List<Field> getAllFieldsList(final Class<?> cls) {
        Validate.isTrue(cls != null, "The class must not be null");
        final List<Field> allFields = new ArrayList<>();
        Class<?> currentClass = cls;
        while (currentClass != null) {
            final Field[] declaredFields = currentClass.getDeclaredFields();
            Collections.addAll(allFields, declaredFields);
            currentClass = currentClass.getSuperclass();
        }
        return allFields;
}