David Withers wrote:
> David Withers wrote:
>
>> Alan Williams wrote:
>>
>>> David Withers wrote:
>>> [snip]
>>>
>>> Hello,
>>>
>>>
>>>> After investigating some more I've found that although the XStream docs
>>>> say "If a new field is added to the class, deserializing an old version
>>>> will leave the field uninitialized", this is not the case. String fields
>>>> are initialized to null, even if you set a default value for the field.
>>>>
>>> What is happening? Are you saying that new fields are initialized to
>>> null? If so, isn't a possible workaround for this to alter the
>>> configuration bean so that when you do a getX it checks if x is null
>>> and, if so, sets it to a value?
>>>
>> If it's a new field that's not in the serialized file then yes, it's
>> initialized to null, even though I'm setting a value when I declare the
>> field, e.g. private String csvDelimiter = ",";
>>
>> So yes, the workaround in this case is:
>>
>> public String getCsvDelimiter() {
>> return outputFormat == null ? "," : csvDelimiter;
>> }
>>
>>
>>
>>>> If you add an enum field then an exception is thrown (which is the
>>>> problem I'm hitting).
>>>>
>>> What is throwing the exception?
>>>
>> XStream. I'm guessing that it creates to object for the field and then
>> sets the value from the serialized xml. However you can't create enums
>> without knowing the value.
>>
>
> Actually I'm wrong there. It seems that because the class is created
> without calling a constructor any values that appear to be assigned as
> part of the field declaration actually aren't assigned.
>
> Oh well, at least I have a workaround now.
>
Its correct that it doesn't call the constructor, because these could
have side affects. Its the same with the getters and setters.
The FAQ recommends adding a readResolve method to do any custom
initialisation required during de-serialisation.
http://xstream.codehaus.org/faq.html (Under "XStream is not calling the
default constructor during deserialization", about a 1/3rd down).
Stuart
> David.
>
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