Copy non-null properties from one object to another using BeanUtils or similar


my aim is to copy fields of one object into another, but only those that aren’t null. I don’t want to assign it explicitly. A more generic solution would be very useful and easier to maintain i.e. for implementing PATCH in REST API where you allow providing only specific fields.

I saw this similar thread and I’m trying to implement some of the ideas from here: Helper in order to copy non null properties from object to another ? (Java)

But the objects aren’t altered in any way after the program execution.

So here are my example classes created for example:

class Person {
    String name;
    int age;
    Pet friend;

    public Person() {

    public Person(String name, int age, Pet friend) { = name;
        this.age = age;
        this.friend = friend;

    // getters and setters here

class Pet {
    String name;
    int age;

    public Pet(String name, int age) { = name;
        this.age = age;

    // getters and setters here

Here is my overridden copyProperty method:

import org.apache.commons.beanutils.BeanUtilsBean;
import java.lang.reflect.InvocationTargetException;

public class MyBeansUtil extends BeanUtilsBean {

public void copyProperty(Object dest, String name, Object value)
        throws IllegalAccessException, InvocationTargetException {
    if(value == null) return;
    super.copyProperty(dest, name, value);

… and here is the place I’m trying to test it on some examples:

public class SandBox {
    public static void main(String[] args) {
        Person db = new Person("John", 36, new Pet("Lucy", 3));
        Person db2 = new Person("John", 36, new Pet("Lucy", 2));
        Person db3 = new Person("John", 36, new Pet("Lucy", 4));

        Person in = new Person();
        in.age = 17; = "Paul";
        in.friend = new Pet(null, 35);

        Person in2 = new Person(); = "Damian";

        Person in3 = new Person();
        in3.friend = new Pet("Lup", 25);

        try {
            BeanUtilsBean notNull  =new MyBeansUtil();
            notNull.copyProperties(db, in);
            notNull.copyProperties(db2, in2);
            notNull.copyProperties(db3, in3);

        } catch (IllegalAccessException e) {
        } catch (InvocationTargetException e) {

Unfortunately, the original objects db, db1, db2 stay the same as they were. Am I doing something wrong here?


I ended up using Spring BeanUtils library. Here is my working method:

import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;

import java.lang.reflect.Field;
import java.util.Collection;

public class MyBeansUtil<T> {
    public T copyNonNullProperties(T target, T in) {
        if (in == null || target == null || target.getClass() != in.getClass()) return null;

        final BeanWrapper src = new BeanWrapperImpl(in);
        final BeanWrapper trg = new BeanWrapperImpl(target);

        for (final Field property : target.getClass().getDeclaredFields()) {
            Object providedObject = src.getPropertyValue(property.getName());
            if (providedObject != null && !(providedObject instanceof Collection<?>)) {
        return target;

It works fine, but notice that it ignores fields that are collections. That’s on purpose, I handle them separately.

Answered By – kiedysktos

This Answer collected from stackoverflow, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0

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