How to Serialize a list in java?

Question

I would like to deep clone a List. for that we are having a method

// apache commons method. This object should be serializable
SerializationUtils.clone ( object ) 

so now to clone my List i should convert that to serializable first. Is it possible to convert a List into Serializable list?

Solution 1

All standard implementations of java.util.List already implement java.io.Serializable.

So even though java.util.List itself is not a subtype of java.io.Serializable, it should be safe to cast the list to Serializable, as long as you know it's one of the standard implementations like ArrayList or LinkedList.

If you're not sure, then copy the list first (using something like new ArrayList(myList)), then you know it's serializable.

Solution 2

As pointed out already, most standard implementations of List are serializable. However you have to ensure that the objects referenced/contained within the list are also serializable.

Solution 3

List is just an interface. The question is: is your actual List implementation serializable? Speaking about the standard List implementations (ArrayList, LinkedList) from the Java run-time, most of them actually are already.

Comments

[Jesper]

Why would anyone ever want to cast anything to Serializable? Serializable is only a marker interface; casting something to Serializable isn't useful.

[skaffman]

Because SerializationUtils.clone() requires an argument on type Serializable, and so if your variable is of type List, you'll need to cast it.

[Zack Marrapese]

@Jesper: It's a marker interface that says it's safe to serialize the class. Android uses the Serializable interface for many things; passing along intent extras, shared preferences, etc.

[Evi Song]

Yes, I found this question when searching Android solutions. My addition is, List<MyClass> myObjs = new ArrayList<MyClass>(); doesn't meet the Serializable, but ArrayList<MyClass> myObjs = new ArrayList<MyClass>(); does.

[arne.b]

As pointed out already, List is an interface that does not extend Serializable or any interface that does so. Lists that are not serializable may not be common in standard libraries, but that does not make the first sentence right.

[Blundell]

@EviSong because the interface List is not serializable. Your declaring your variable of type List.

[aakoch]

If I have a bean that contains a List of serializable objects, should I put a check in the setter to make sure the List is serializable since I won't know what kind of list is being set?

[Theodore Murdock]

@Adam It might be best to guarantee safety at compile-time instead by using the signature <T extends List<Foo> & Serializable> setFooList(T list), which requires your caller to pass you an instance of some List implementation that is also Serializable.

[MG Developer]

List is not but implementation classes like ArrayLists are serializable. You can use them.