Retrieving the inherited attribute names/values using Java Reflection

java

reflection

field-utils

apache-commons-lang

byAlex Kataev·Oct 7, 2024

You can procure public and non-public fields of an object and its superclasses using Java Reflection. Just stroll up the class hierarchy with getDeclaredFields and set them accessible.

Object obj = // ... inauguration day, let the object instance step in
Class<?> cls = obj.getClass();
while (cls != null) {
    for (Field field : cls.getDeclaredFields()) {
        field.setAccessible(true); // No field left behind! Let's pry open those private/protected ones
        System.out.println(field.getName() + ": " + field.get(obj));
    }
    cls = cls.getSuperclass(); // Keep climbing up the family tree
}

This snippet declaims every single field name and value, including ones passed down from ancestors, for the specified object (obj). Keep an eye out for IllegalAccessException when attempting to access fields.

Fine-tuning field retrieval

The fast answer cruises to the destination, but let's slow down and take a scenic route. Parsing the fields from classes and superclasses, and storing them for further usage.

Gathering all fields in a list

Here's a public static method to not just print but collect fields:

public static List<Field> getAllFields(List<Field> fields, Class<?> type) {
    fields.addAll(Arrays.asList(type.getDeclaredFields())); // Collecting all our belongings
    
    if (type.getSuperclass() != null) { // As long as there's an ancestor
        fields = getAllFields(fields, type.getSuperclass()); // Recursion, Ah! sweet inheritance 
    }
    return fields; // Can't return empty-handed, can we now?
}

The Apache Way

Save the day using FieldUtils.getAllFieldsList from Apache Commons Lang (version 3.2+ required), to avoid the hustle:

List<Field> allFields = FieldUtils.getAllFieldsList(obj.getClass());
allFields.forEach(field -> {
    field.setAccessible(true);
    System.out.println(field.getName()); // Field printout, coming right up!
});

Don't forget the Test Drive

Put your code on a test bench before letting it out in the wild. Render it immune to quirks of complex class hierarchies and make sure it fetches all the fields.