Copying JavaBeans Instances
External
Internal
Overview
This article describes methods of copying Java Bean instances in such a way that changing the copy leaves the original object intact.
Object.clone()
This method can be used when we have access to the JavaBeans instance class code.
Essentially, the cloned object should generally behave as follows (though this is not a requirement):
x.clone() != x
x.clone.getClass() == x.getClass();
x.clone().equals(x)
By convention, the returned object should be obtained by calling super.clone(). If a class and all of its superclasses (except Object) obey this convention, x.clone().getClass() == x.getClass() will be true.
/**
* Creates and returns a copy of this object. The precise meaning
* of "copy" may depend on the class of the object. The general
* intent is that, for any object {@code x}, the expression:
*
*
* x.clone() != x
* will be true, and that the expression:
*
*
* x.clone().getClass() == x.getClass()
* will be {@code true}, but these are not absolute requirements.
* While it is typically the case that:
*
*
* x.clone().equals(x)
* will be {@code true}, this is not an absolute requirement.
*
* By convention, the returned object should be obtained by calling * {@code super.clone}. If a class and all of its superclasses (except * {@code Object}) obey this convention, it will be the case that * {@code x.clone().getClass() == x.getClass()}. *
* By convention, the object returned by this method should be independent * of this object (which is being cloned). To achieve this independence, * it may be necessary to modify one or more fields of the object returned * by {@code super.clone} before returning it. Typically, this means * copying any mutable objects that comprise the internal "deep structure" * of the object being cloned and replacing the references to these * objects with references to the copies. If a class contains only * primitive fields or references to immutable objects, then it is usually * the case that no fields in the object returned by {@code super.clone} * need to be modified. *
* The method {@code clone} for class {@code Object} performs a * specific cloning operation. First, if the class of this object does * not implement the interface {@code Cloneable}, then a * {@code CloneNotSupportedException} is thrown. Note that all arrays * are considered to implement the interface {@code Cloneable} and that * the return type of the {@code clone} method of an array type {@code T[]} * is {@code T[]} where T is any reference or primitive type. * Otherwise, this method creates a new instance of the class of this * object and initializes all its fields with exactly the contents of * the corresponding fields of this object, as if by assignment; the * contents of the fields are not themselves cloned. Thus, this method * performs a "shallow copy" of this object, not a "deep copy" operation. *
* The class {@code Object} does not itself implement the interface * {@code Cloneable}, so calling the {@code clone} method on an object * whose class is {@code Object} will result in throwing an * exception at run time. * * @return a clone of this instance. * @throws CloneNotSupportedException if the object's class does not * support the {@code Cloneable} interface. Subclasses * that override the {@code clone} method can also * throw this exception to indicate that an instance cannot * be cloned. * @see java.lang.Cloneable */
BeanUtils
org.apache.commons.beanutils.BeanUtils is a utility method for populating JavaBeans properties via reflection. This method can be used even if we don't have access to the JavaBeans instance class code.