On Tue, Nov 15, 2011 at 10:30 PM, Gerald Tan woefulwab...@gmail.com wrote:
Only Serializable objects can be used as properties, and Cipher isn't
serializable. The solution is to store the algorithm as a String, then
reinstantiating the Cipher from the algorithm string after retrieving it
from the datastore.
This is almost right - it's not about being Serializable.
GAE only lets you store certain basic types (Long, String, Text, Blob,
GeoPt, and about a dozen others including collections of these types).
They aren't stored with java serialization; I believe the native structure
is protobuf but this is opaque outside of Google. Objectify extends this
list somewhat by automatically converting some types into ones the
datastore recognizes (for example, String[] into ListString, byte[] into
Blob, fields with @Serialized annotation into Blob, etc). But there are
practical limits. We didn't go through every single JDK class figuring out
how to store it in appengine.
Cipher, IvParameterSpec, SecretKeySpec are not storeable types. Cipher
doesn't even make sense to store - you probably just want to store the
algorithm with which the Cipher was created. IvParameterSpec and
SecretKeySpec are probably best stored as byte[] (which Ofy will convert to
Blob) or, if you prefer, can be Base64 or hex encoded into a String.
There are situations when you will want to build Objectify Converters so
that fields can have normal types; for example, if you use Joda Time or
Joda Money classes (Objectify includes converters for these, but they
aren't enabled by default). I won't tell you that it's wrong to use
IvParameterSpec and SecretKeySpec fields, but for the most part you should
be cautious of using exotic types in your data model - especially when they
are interfaces without a concrete type definition. I wouldn't do it.
Jeff
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