RFR [9] 8071472: Add field access to support setting final fields in readObject

[Alan Bateman]

On 05/03/2015 13:46, Chris Hegarty wrote:
> :
>
> Example:
>      class Stamp implements Serializable {
>          private transient final long millis;
>          Stamp() { millis = System.currentTimeMillis(); }
>          public long stamp() { return millis; }
>
>          private void readObject(java.io.ObjectInputStream in) throws Exception {
>              in.fields().set("millis", System.currentTimeMillis());
>          }
>      }
>
> We have a fully working implementation, tests, etc, in the sandbox:
>      hg clone http://hg.openjdk.java.net/jdk9/sandbox sandbox
>      cd sandbox
>      sh get_source.sh
>      sh common/bin/hgforest.sh update -r serial-exp-branch
>      
>    Webrev for convenience:
>      http://cr.openjdk.java.net/~chegar/8071472/00/webrev/
>
I've spent some time looking at this and trying it out. It's very 
simple, doesn't impact any existing readObject implementations, and 
provides a way to set final fields without restoring to Unsafe.

So if a readObject calls fields() without calling defaultReadObject() 
then it has to set every final field. On one hand that ensures that 
every final field is set, on the other hand it is a bit odd because 
omitting the call to fields() means they all get their default value.

I think serialization types with final fields that aren't in the 
serialized form will really like this. To help developers then it might 
be useful to put an example in the javadoc with final && transient field 
to show the usage.

One other thing is naming as OIS.FieldAccess in the current patch hints 
that it provides general access. It feels like it should be something 
like ObjectFieldSetter with fields() changing to something like 
fieldSetter() to make that clearer too.

-Alan.