Voici une petite précision qui n’a l’air de rien mais qui a son importance.

Quand vous avez une classe qui implémente l’interface Serializable, pensez à créer l’attribut « serialVersionUID« .

En général Eclipse vous invite à le faire et vous propose de le générer automatiquement (ne prenez pas la valeur bidon) via le quick fix.

Je vous renvoie vers le Javadoc : http://download.oracle.com/javase/1.5.0/docs/api/java/io/Serializable.html

The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender’s class, then deserialization will result in an InvalidClassException. A serializable class can declare its own serialVersionUID explicitly by declaring a field named « serialVersionUID » that must be static, final, and of type long:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class–serialVersionUID fields are not useful as inherited members.

Alors à quoi ça sert ? Et ben c’est vrai que ce n’est pas hyper indispensable sur un petit projet « standalone » mais ça le devient dans un projet JBoss dans une ferme…