Class not included in the set of types for RPC

Neil Aggarwal

unread,

Dec 18, 2024, 11:46:31 PM12/18/24

to google-we...@googlegroups.com

I am getting this error on the server:
Type 'com.propfinancing.puzzle.slitherlink.Line' was not included in the
set of types which can be
serialized by this SerializationPolicy or its Class object could not be
loaded. For security purposes,
this type will not be serialized.: instance = Line 0

And looking in the .gwt.rpc file, it is not listed there.

Interestingly, I see this:
com.propfinancing.puzzle.slitherlink.Line$STATUS
which is an Enum in that class so the GWT compiler obviously processed the
class.

I did not get any warnings or error messages from the GWT compiler as to
why it
decided it did not like the class so now I have to guess what it did not
like.

Is there a way to improve the messaging to the user to help understand
what happened?

Thank you,
Neil

--
Neil Aggarwal, (972) 834-1565, http://www.propfinancing.com
We offer 30 year loans on single family houses!

Craig Mitchell

unread,

Dec 19, 2024, 2:08:53 AM12/19/24

to GWT Users

At a guess, the inner enum needs to be told it can be serialised. Ie:

import com.google.gwt.user.client.rpc.IsSerializable;

enum STATUS implements IsSerializable { ... }

Colin Alworth

unread,

Dec 19, 2024, 9:19:28 AM12/19/24

to GWT Users

Enums never need to be marked as serializable - unlike records, the Enum type itself is always serializable, and GWT-RPC assumes the same. From https://www.gwtproject.org/doc/latest/DevGuideServerCommunication.html#DevGuideSerializableTypes

A type is serializable and can be used in a service interface if one of the following is true:

...

* The type is an enumeration. Enumeration constants are serialized as a name only; none of the field values are serialized.

That error message is indeed what is used when the standard serialization policy is read from disk, so you've resolved that earlier issue. Can you confirm that the policy file does include Line (that is, it is correctly reachable from the remote service instance)? If not, the GWT-RPC generator (run when the compiler is invoked) might not have seen a clear path to how this type could be used. Common reasons for that include declaring a field as being of type Object, which in your head means that any type could be assigned, but GWT-RPC doesn't want to mark every possibly class as potentially serializable (both for security reasons and to avoid generating serialization code for your client for every possible type).

Neil Aggarwal

unread,

Dec 19, 2024, 11:12:06 AM12/19/24

to google-we...@googlegroups.com

> Enumeration constants are serialized as a name only; none of the field values are serialized.

What are the consequences of not having the values?

Reading on the Internet, it means I can’t use valueOf() and ordinal().

But, does it work normally otherwise?

Can I assign a constant value to a field, read that value, and compare the value to one of the
constants?

> Can you confirm that the policy file does include Line

It does not have Line in it:

@FinalFields, true

com._3dmathpuzzles.play.client.GetPuzzleService, false, false, false, false, _, 4203465842

com._3dmathpuzzles.slitherlink.RectangularWithDiagonalsPuzzle, true, true, false, false, com._3dmathpuzzles.slitherlink.RectangularWithDiagonalsPuzzle/2547295082, 2547295082

com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException, true, true, true, true, com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException/3936916533, 3936916533

com.google.gwt.user.client.rpc.RpcTokenException, true, true, false, false, com.google.gwt.user.client.rpc.RpcTokenException/2345075298, 2345075298

com.google.gwt.user.client.rpc.XsrfToken, false, false, true, true, com.google.gwt.user.client.rpc.XsrfToken/4254043109, 4254043109

com.propfinancing.puzzle.Puzzle, true, false, false, false, com.propfinancing.puzzle.Puzzle/1723715424, 1723715424

com.propfinancing.puzzle.slitherlink.Box, true, true, false, false, com.propfinancing.puzzle.slitherlink.Box/1302152982, 1302152982

com.propfinancing.puzzle.slitherlink.Box$STATE, true, true, false, false, com.propfinancing.puzzle.slitherlink.Box$STATE/1639054469, 1639054469

com.propfinancing.puzzle.slitherlink.BoxWithDiagonals, true, true, false, false, com.propfinancing.puzzle.slitherlink.BoxWithDiagonals/2774485663, 2774485663

com.propfinancing.puzzle.slitherlink.Component, true, false, false, false, com.propfinancing.puzzle.slitherlink.Component/4011233562, 4011233562

com.propfinancing.puzzle.slitherlink.Line$STATUS, true, true, false, false, com.propfinancing.puzzle.slitherlink.Line$STATUS/1640439993, 1640439993

com.propfinancing.puzzle.slitherlink.NumberedBox, true, true, false, false, com.propfinancing.puzzle.slitherlink.NumberedBox/1782628205, 1782628205

com.propfinancing.puzzle.slitherlink.Puzzle, true, false, false, false, com.propfinancing.puzzle.slitherlink.Puzzle/2584703185, 2584703185

com.propfinancing.puzzle.slitherlink.RectangularPuzzle, true, false, false, false, com.propfinancing.puzzle.slitherlink.RectangularPuzzle/3177548746, 3177548746

com.propfinancing.puzzle.slitherlink.RectangularWithDiagonalsPuzzle, true, false, false, false, com.propfinancing.puzzle.slitherlink.RectangularWithDiagonalsPuzzle/3793384887, 3793384887

java.lang.Exception, true, false, true, false, java.lang.Exception/1920171873, 1920171873

java.lang.RuntimeException, true, false, true, false, java.lang.RuntimeException/515124647, 515124647

java.lang.String, true, true, true, true, java.lang.String/2004016611, 2004016611

java.lang.Throwable, true, false, true, false, java.lang.Throwable/2953622131, 2953622131

java.util.ArrayList, true, true, false, false, java.util.ArrayList/4159755760, 4159755760

java.util.HashMap, true, true, false, false, java.util.HashMap/1797211028, 1797211028

java.util.LinkedHashMap, true, true, false, false, java.util.LinkedHashMap/3008245022, 3008245022

> the GWT-RPC generator (run when the compiler is invoked) might not have seen a clear path to how this type could be used

Unfortunately, it is silent about the reason.

I am hoping we can improve it help the developer instead of leaving me to make guesses.

Jens

unread,

Dec 19, 2024, 4:41:11 PM12/19/24

to GWT Users

Neil Aggarwal schrieb am Donnerstag, 19. Dezember 2024 um 17:12:06 UTC+1:

> Enumeration constants are serialized as a name only; none of the field values are serialized.
What are the consequences of not having the values?

The consequence is that your enums should never ever have changing data stored. For example MyEnum.PERSON.getFriends().add(friend) is possible in Java but makes the enum constant mutable, which is bad. If enum constants are immutable then serializing the name or ordinal is enough to reconstruct the state.

> Can you confirm that the policy file does include Line
It does not have Line in it:

Does Line satisfy all rules? Default constructor, implements Serializable and only has Serializable fields? If yes, take a look at your GWT-RPC service method(s) declaration. Starting from the return type and the parameter types of the GWT-RPC method(s), will Line be discoverable directly or is it hidden behind some interface or super class or possibly class Object and GWT would need to find all the candidates that match these interfaces/super classes? If Line is hidden, do the interface / super class follow the rules? Maybe Line isn't the only class that is missing in the policy file?

As a workaround you can always add dummy methods to your GWT-RPC service, e.g. Line getDummyLine(), to make a class visible to GWT (or a Dummy class with a Line field and then use Dummy as return type).

-- J.

Colin Alworth

unread,

Dec 19, 2024, 4:46:55 PM12/19/24

to GWT Users

Improving the explanation of why Line isn't present would require exhaustively listing all the possible fields/etc that where is _isn't_ valid to assign a Line instance - Line isnt a subtype of String, Line isn't a subtype of List, the List in this field is List<Component> and Line isn't a subtype of Component, etc...

If you can point out in code how you expect to be able to send the Line type (which field in which other type that _is_ present in that list) it would be easier to offer an explanation.

Neil Aggarwal

unread,

Dec 19, 2024, 5:31:22 PM12/19/24

to google-we...@googlegroups.com

> Improving the explanation of why Line isn't present would require exhaustively listing all the possible

> fields/etc that where is _isn't_ valid to assign a Line instance

An exhaustive irrelevant list might be worse.

I was thinking it might be something within the class which the compiler did not like.

> If you can point out in code how you expect to be able to send the Line type (which field in which other

> type that _is_ present in that list) it would be easier to offer an explanation.

com.propfinancing.puzzle.slitherlink.Box is in the list.

It has this field:

private ArrayList<Line> lines;

Neil Aggarwal

unread,

Dec 19, 2024, 5:43:59 PM12/19/24

to google-we...@googlegroups.com

> The consequence is that your enums should never ever have changing data stored

Got it. I never modify the enum via code. That would be a bit strange.

> Maybe Line isn't the only class that is missing in the policy file?

Yes, there are others which are missing.

> As a workaround you can always add dummy methods to your GWT-RPC service, e.g.

> Line getDummyLine(), to make a class visible to GWT

I added this method to com.propfinancing.puzzle.slitherlink.Box:

public Line gwtGetLine() {

return new Line();

}

And the generated .gwt.rpc has Box, but still does not have Line: