GWT\'s serializer has limited java.io.Serializable support, but for security reasons there is a whitelist of types it supports. The documentation I\'ve found,
The whitelist is generated by the GWT compiler and contains all the entries that are designated by the IsSerializable marker interface.
To add a type to the list you just need to make sure that the class implements the IsSerializable interface.
Additionally for serialization to work correctly the class must have a default no arg constructor (constructor can be private if needed). Also if the class is an inner it must be marked as static.