JDK 9 RFR of JDK-6226715: (ann) java.lang.annotation.AnnotationTypeMismatchException could not be serialized

[Roger Riggs]

Joe,

Caveats and all, that seems like a good solution.
+1

Roger


On 6/30/2016 1:18 PM, joe darcy wrote:
> Hello,
>
> Please review the changes to address
>
>     JDK-6226715: (ann) 
> java.lang.annotation.AnnotationTypeMismatchException could not be 
> serialized
>     http://cr.openjdk.java.net/~darcy/6226715.0/
>
> Patch below.
>
> The analysis of why is patch is valid requires a bit of explanation.
>
> Like all other exceptions, AnnotationTypeMismatchException is 
> serializable. However, its state contains a non-serializable element 
> field of type Method. Therefore, previously an 
> AnnotationTypeMismatchException with a non-null element field threw an 
> exception when serialized. Therefore, the only persisted 
> AnnotationTypeMismatchException objects have null element fields in 
> the serial output.
>
> The patch changes element to be a transient field, removing it from 
> the serial output, *without* changing the serialVersionUID. This would 
> not usually be a valid transformation, but limits on what can be 
> serialized make it acceptable in this case.
>
> If an old serialized form of an AnnotationTypeMismatchException object 
> with a null value for element is deserialized after the patch, the now 
> extraneous element information is ignored, yielding a semantically 
> correct object (with a null value for element).
>
> If a new serialized form is deserialized against the previous version 
> of AnnotationTypeMismatchException, the information for the element 
> field is missing, but it gets defaulted to be null, again giving the 
> correct semantics.
>
> I've verified this cross-version behavior.
>
> While subtle, I think this change is preferable to introducing 
> readObject/writeObject methods to do something like explicit write out 
> a null value for the element field in the serial form even if element 
> is non-null, etc.
>
> The specification updates make the possibility of nulls explicit.
>
> Thanks,
>
> -Joe
>
>
> --- 
> old/src/java.base/share/classes/java/lang/annotation/AnnotationTypeMismatchException.java 
> 2016-06-30 09:53:08.335033457 -0700
> +++ 
> new/src/java.base/share/classes/java/lang/annotation/AnnotationTypeMismatchException.java 
> 2016-06-30 09:53:08.223033453 -0700
> @@ -44,7 +44,7 @@
>      /**
>       * The {@code Method} object for the annotation element.
>       */
> -    private final Method element;
> +    private final transient Method element;
>
>      /**
>       * The (erroneous) type of data found in the annotation. This string
> @@ -57,10 +57,12 @@
>       * Constructs an AnnotationTypeMismatchException for the specified
>       * annotation type element and found data type.
>       *
> -     * @param element the {@code Method} object for the annotation 
> element
> +     * @param element the {@code Method} object for the annotation
> +     * element, may be {@code null}
>       * @param foundType the (erroneous) type of data found in the 
> annotation.
>       *        This string may, but is not required to, contain the value
> -     *        as well.  The exact format of the string is unspecified.
> +     *        as well.  The exact format of the string is unspecified,
> +     *        may be {@code null}.
>       */
>      public AnnotationTypeMismatchException(Method element, String 
> foundType) {
>          super("Incorrectly typed data found for annotation element " 
> + element
> @@ -71,8 +73,11 @@
>
>      /**
>       * Returns the {@code Method} object for the incorrectly typed 
> element.
> +     * The value may be unavailable if this exception has been
> +     * serialized and then read back in.
>       *
> -     * @return the {@code Method} object for the incorrectly typed 
> element
> +     * @return the {@code Method} object for the incorrectly typed
> +     * element, or {@code null} if unavailable
>       */
>      public Method element() {
>          return this.element;
> @@ -81,7 +86,8 @@
>      /**
>       * Returns the type of data found in the incorrectly typed element.
>       * The returned string may, but is not required to, contain the 
> value
> -     * as well.  The exact format of the string is unspecified.
> +     * as well.  The exact format of the string is unspecified and 
> the string
> +     * may be {@code null}.
>       *
>       * @return the type of data found in the incorrectly typed element
>       */
>