Guillaume Guillaume - 9 days ago 6
Java Question

Java: recommended solution for deep cloning/copying an instance

I'm wondering if there is a recommended way of doing deep clone/copy of instance in java.

I have 3 solutions in mind, but I can have miss some, and I'd like to have your opinion

edit: include Bohzo propositon and refine question: it's more about deep cloning than shallow cloning.

Do it yourself:



code the clone by hand properties after properties and check that mutable instances are cloned too.

pro:

- control of what will be performed

- quick execution

cons:

- tedious to write and maintain

- bug prone (copy/paste failure, missing property, reassigned mutable property)

Use reflection:



With your own reflection tools or with an external helper (like jakarta common-beans) it is easy to write a generic copy method that will do the job in one line.

pro:

- easy to write

- no maintenance

cons:

- less control of what happens

- bug prone with mutable object if the reflection tool does not clone sub objects too

- slower execution

Use clone framework:



Use a framework that do it for you, like :

commons-lang SerializationUtils

Java Deep Cloning Library

Dozer

Kryo

pro:

- same as reflection

- more control over what will be exactly be cloned.

cons:

- every mutable instance is fully cloned, even at the end of the hierarchy

- could be very slow to execute

Use bytecode instrumentation to write clone at runtime



javassit, BCEL or cglib might be use to generate a dedicated cloner as fast as one hand writed. Someone knows a lib using one of these tools for this purpose ?

What I have missed here ?

Which one would you recommend ?

Thanks.

Answer

For deep cloning (clones the entire object hierarchy):

  • commons-lang SerializationUtils - using serialization - if all classes are in your control and you can force implementing Serializable.

  • Java Deep Cloning Library - using reflection - in cases when the classes or the objects you want to clone are out of your control (a 3rd party library) and you can't make them implement Serializable, or in cases you don't want to implement Serializable.

For shallow cloning (clones only the first level properties):

I deliberately omitted the "do-it-yourself" option - the API's above provide a good control over what to and what not to clone (for example using transient, or String[] ignoreProperties), so reinventing the wheel isn't preferred.