BeanUtils.copyProperties convert Integer null to 0

Question

I noticed that BeanUtils.copyProperties(dest, src) has a strange side effect. All null Integers (probably Long, Date etc. too) convert to 0 in both objects: source (sic!) and destination. Version: commons-beanutils-1.7.0

javadoc:

Copy property values from the origin bean to the destination bean for all cases where the property names are the same.

For example:

class User {
   Integer age = null;
   // getters & setters
}
...
User userDest = new User();
User userSrc = new User();
BeanUtils.copyProperties(userDest, userSrc);
System.out.println(userDest.getAge()); // 0
System.out.println(userSrc.getAge()); // 0

It can be very buggy that source object is actually modified. What is the best solution to make "real" copy of object with null value.

Answer 1

Ok I've found this post

There is however a big difference between these two classes which I came across while using these classes: BeanUtils does an automatic type conversion and PropertyUtils does not.

For example: with BeanUtils you can set a double valued property by providing a String. BeanUtils will check the type of the property and convert the String into a double. With PropertyUtils you always have to provide a value object of the same type as the property, so in this example a double.

Automatic conversion is not necessary in this case, so better choice is PropertyUtils class

Answer 2

Checking http://commons.apache.org/beanutils/api/org/apache/commons/beanutils/ConvertUtilsBean.html it indicates the default for Integer conversion is 0. This is because the destination type here is the primitive int or reference int and primitive int cannot be set to null.

You can override the converter for Integer and replace it with one whose default value is null.

UPDATE: Usage is

import org.apache.commons.beanutils.converters.IntegerConverter;

IntegerConverter converter = new IntegerConverter(null); 
BeanUtilsBean beanUtilsBean = new BeanUtilsBean();
beanUtilsBean.getConvertUtils().register(converter, Integer.class);

Take a look at the source code for IntegerConverter - you set the default value in the constructor.