JDK 14 RFR of JDK-8231202: Suppress warnings on non-serializable non-transient instance fields in serializable classes
joe.darcy at oracle.com
Wed Sep 18 21:38:59 UTC 2019
As background, I'm working on a number of serialization-related
compile-time checks with the goal of enabling stricter javac lint
checking in the JDK build (and elsewhere).
One check is tracked by
JDK-8160675: Issue lint warning for non-serializable non-transient
instance fields in serializable type
As summarized in the bug description, it may be concerning if a
serializable class has non-transient instance fields whose types are not
Serializable. This can cause a serialization failure at runtime.
(Classes using the serialPersistentFields mechanism are excluded from
A common example is an exception type -- all Throwable's are
Serializable -- which has a non-serializable field. If the fields cannot
be marked as transient, one approach to handle this robustly is to have
a writeObject method which null outs the field in question when
serializing and make the other methods in the exception null-tolerant.
In other cases, the object pointed to by the non-serializable field are
conditionally serializable at runtime. This is the case for many
collection types. For example, a class may have a field of type
List<Foo> with the field set to an ArrayList<Foo> at runtime. While the
List interface does not extent Serializable, the ArrayList class does
implement Serializable and the class would serialize fine in practice,
assuming the Foo's were serialazable.
As a precursor to the adding a compile-time check to the build, please
review adding @SuppressWarnings("serial") to document the
non-serializable fields in the core libraries:
JDK-8231202: Suppress warnings on non-serializable non-transient
instance fields in serializable classes
Bugs for similar changes to client libs and security libs will be filed
and reviewed separately.
A more complete fix would add readObject/writeObject null handling to
AnnotationTypeMismatchExceptionProxy, but since this hasn't seemed to be
an issue since the type was introduced back in JDK 5.0, I just added the
annotation, as done elsewhere.
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