A good way to find unserializable fields in Java

Question

I have a quite complex Java object to serialize (which worked fine a couple of weeks ago). After having implemented a lot in the meantime, the serialization now fails throwing t

Answer 1

The library class can be assumed to be correctly serializable, i.e. to declare all non-serializable fields as transient, and therefore shouldn't be the source of the error.

If your code is using ContextedRuntimeExceptions, they are an exception to the above rule because the objects they reference may not be serializable, and this is noted in the Javadoc at the methods addContextValue() and setContextValue(). If context values are the problem, it would explain why the suspect classes got a reference to a Graphics2D object without having such a field.

I have had limited success replicating NotSerializableException for SunGraphics2D without leaving an obvious field with "Graphics" in its name laying around, which could be due to testing on a simpler class structure. I found that in addition to contexted exceptions, collections were a good suspect but only if they used raw types. Collections could also cause intermittent failures if they were only sometimes populated with Graphics.

Depending on your application, Ben Lawry's automated solution to a similar issue may be easier to implement than manually hunting for the above. If that path works, it will likely be more thorough as well. Can you get a stack trace?