We need a CacheLoader decorator able to chain sets of two different Externalizers which are targeting the same Java type to transform from one binary format to the next binary format.

Example: a Person object stored in the cache and an Externalizer is coupled to it. In a new release the Externalizer is changed to provide a different binary representation. Using the old one the stream is transformed from a byte[] to a Person, then this Java instance is feed to the new Externalizer implementation to get the new corresponding byte[]; the updated stream is stored in the decorated CacheLoader so that the nodes going to be attached to the cache store and using the new Externalizer will be fine.

A little complexity is introduced if the cache has to know about different sets of Externalizers if several different types need to be upgraded. A possible solution is to use a single decorator instance for each type, creating a chain of decorators if they are able to pass "as is" each externalizer id they are not directly coupled to.