如何在Java中将子集的属性子集从Bean A复制到Bean B？

Question

Essentially what I am looking for is an easy method like:

BeanUtils.copyProperties(dest, orig);

This comes from apache but copies all properties from the origin to the destination. I need something that will only copy a certain subset of properties... something like the following

String[] propertyNamesToCopy = {"firstName", "lastName"};
BeanUtils.copyProperties(dest, orig, propertyNamesToCopy);

Any suggestions?

Answer 1

You can use copyProperty from BeanUtils for copying a single property. Just loop over your properties and use it. You can extract it into a method.

Answer 2

You could do it with reflection.

public void copyProperties(Object orig, Object dest, String[] props){

    Class<?> class = orig.getClass().getFields();
    for(String fieldName : props){
       Field field = class.getField( fieldName );
       field.set(dest, field.get(orig));
    }
}

I didn't try it out, and you might have several problems with this method.

First you need to add try/catch in case the field does not exist. Then it only works for public fields. Also, the get() method form Field returns only objects and I don't know if it will autobox/unbox them or not which might generate runtimes erros and force you to use getInt() , etc... depending on FieldType (you can get it with field.getGenericType() ). You might see getDeclaredField() which get all the field (even privates) but only for the class you have, not the field inherited from parents.

If you want to access private field, either set them to public using reflection ( field.setaccessible(true) if I am correct) or access them through their getters and setters (also using reflection):

Method get = class.getMethod("get"+fieldNameWithCaps); 
Object newValue = get.invoke(orig)
Method set = class.getMethod("set"+fieldNameWithCaps, newValue.getClass()); 
set.invoke(dest, newValue);

Still not sure here as I don't know what newValue.getClass() will return, but you get the idea. Try looking around reflection, but be carefull, it's quite slow and can be messy.

Answer 3

The BeanUtils class from Spring provides essentially the inverse of what I was looking for. So I take the list of all properties - list of properties to copy to get the ignore list but it works :-)

org.springframework.beans.BeanUtils.copyProperties(Object source, Object target, String... ignoreProperties)