FXMLLoader: not supplying filename to script engine, not supplying event object as argument to script

Michael Paus mp at jugs.org
Wed Nov 13 14:40:17 UTC 2019

have you considered directly contributing your proposed change via a PR on
<https://github.com/openjdk/jfx>? According to my experience this may speed
up things considerably but don't forget to follow the procedures as 
outlined in

Am 13.11.19 um 15:14 schrieb Rony G. Flatscher:
> Hmm, not getting any feedback so far, so wondering if there are currently any Java developers who
> take advantage of the ability of FXMLLoader to have FXML controllers implemented in any of the Java
> javax.script languages?
> For those, who use scripting languages for FXML controllers the request that FXMLLoader adds both
> entries, ScriptEngine.FILENAME (for debugging, logging) and ScriptEngine.ARGV () (for making the
> event object available directly as an argument) into the engine Bindings, should be quite helpful
> while developing and running the scripts.
> [Personally I am using the scripting engine ooRexx successfully for teaching oo programming from
> scratch to JavaFX in a single semester (four hour lecture, eight ECTS) at a Business Administration
> university. So these two missing features in the current FXMLLoader support for FXML controllers
> would help tremendously, especially in case of coding errors as currently it is not clear from which
> file the script that has an error comes from, making it extremely cumbersome and time consuming in
> JavaFX applications that use multiple and complex FXML files.]
> Therefore I would kindly ask interested committers for mentoring the proposed changes. Enclosed
> please find a simpler version of the patch that adds these missing features to the ENGINE_SCOPE
> Bindings in the three locations where ScriptEngine.eval() gets invoked (it ).
> To comment this simple patch, maybe I should add a few remarks such that the context becomes clear:
>    * invoking a script via ScriptEngine.eval() will always be accompanied with a ScriptContext that
>      usually maintains two Bindings (Maps):
>        o one, GLOBAL_SCOPE Bindings, for global entries (used e.g. for putting the FXML elements that
>          have an fx:id attribute defined, such that scripts can get access to them, independent of a
>          particular ScriptEngine) which can also be used for sharing values among different script
>          invocations,
>        o one, ENGINE_SCOPE Bindings, usually used for individual invocations.
>    * while a FXML file gets processed sequentially by the FXMLLoader elements in the form of
>      "<fx:script source="someScript.ext" />" will cause invoking the ScriptEngine.eval(Reader): this
>      patch fetches the ENGINE_SCOPE Bindings and puts the value "someScript.ext" with the key
>      ScriptEngine.FILENAME into it (cf. "@@ -1558,6 +1558,9 @@ public class FXMLLoader" and "@@
>      -1582,6 +1585,8 @@ public class FXMLLoader" in the patch),
>    * if an event handler gets defined (e.g. with the event attribute "<fx:button ...
>      onAction="someScript">") the FXMLLoader creates a ScriptEventHandler and stores "someScript" and
>      the ScriptEngine for executing that script whenever the event fires.
>        o When an event fires, the current implementation creates a copy of the current ENGINE_SCOPE
>          Bindings from the ScriptEngine's ScriptContext, adds its entries to it after saving the
>          entry "event" with the ActionEvent object in it. It then changes the ScriptEngine's current
>          ScriptContext such that it now uses the new copy of the Bindings as its ENGINE_SCOPE
>          Bindings, runs the script using eval() and then restores the ScriptContext ENGINE_SCOPE
>          Bindings.
>        o The supplied patch (cf. "@@ -1675,30 +1680,28 @@ public class FXMLLoader") instead will
>          create a copy of the ENGINE_SCOPE Bindings only once at creation time (and puts the
>          appropriate ScriptEngine.FILENAME into it using the name of the FXML file that defines the
>          event script attribute) and will reuse that Bindings each time the handler gets invoked,
>          after putting the actual "event" object and the respective ScriptEngine.ARGV entry into it.
>          Using ScriptEngine.eval(String,Bindings) will use the supplied Bindings as the ENGINE_SCOPE
>          Bindings for this invocation only, such that no restore is necessary upon return.
> As only entries get added to the engine Bindings that have not been used by FXMLLoader this simple
> patch should not affect existing scripts. The patch has been tested and works.
> Maybe it helps the cause for applying this patch, if I point out that I have been active in a number
> of opensource projects, including Apache's BSF which led to my participation as an expert in JSR-223
> which originally defined the javax.script framework introduced with Java 6 (also authored a complete
> ScriptEngine implementation with both, the javax.script.Compilable and the javax.script.Invocable
> interfaces).
> So looking for interested committers who would be willing to mentor this patch. Please advise.
> ---rony
> On 06.11.2019 16:05, Rony G. Flatscher wrote:
>> Using a script engine (javax.script.ScriptEngine) for implementing a FXML controller there are two
>> important information missing in the ScriptContext.ENGINE_SCOPE Bindings supplied to the script used
>> to eval() the script code:
>>    * ScriptEngine.FILENAME
>>        o This value denotes the file name from where the script code was fetched that is being eval()'d.
>>        o When debugging script controllers in a complex JavaFX application it is mandatory to know
>>          the file name the script code was taken from (as such scripts could be called/run from
>>          different FXML files). Also, in the case of script runtime errors, usually the file name is
>>          given by the script engine where the error has occurred to ease debugging, such that it is
>>          important to really supply the filename.
>>            + Note: the 'location'-URL in ScriptContext.GLOBAL_SCOPE refers the FXML file,  not to the
>>              file that hosts the script that gets run if using the "<fx:script" element where the
>>              "source" attribute denotes the name of the script file.
>>        o General solution: supply the appropriate ScriptEngine.FILENAME entry to the
>>          ScriptContext.ENGINE_SCOPE Bindings.
>>    * ScriptEngine.ARGV
>>        o This value denotes the arguments that get passed to the script from Java in form of a Java
>>          Array of type Object.
>>        o When defining event handlers in FXML files in script code the script does not get the
>>          appropriate argument. Rather the script programmer needs to access the
>>          ScriptContext.ENGINE_SCOPE and fetch the entry named "event" from there. Some script engines
>>          may make the entries in the Bindings implicitly available to the scripts, however this
>>          cannot be expected by default. However, a ScriptEngine.ARGV entry must be supplied to the
>>          script by the script engine implementor, such that a script coder gets the event object
>>          argument in the script language's manner.
>>        o General solution: supply the appropriate ScriptEngine.ARGV Object array to the
>>          ScriptContext.ENGINE_SCOPE Bindings.
>> With these two changes not only writing controller scripts would be eased, it also would
>> instrumentate ScriptContext.ENGINE_SCOPE Bindings the way it was intended by JSR-223.
>> Enclosed please find a tested diff for FXMLLoader.java from the current OpenJavaFX Master (version
>> 14) that implements both, ScriptEngine.FILENAME entries for all script invocations and in the case
>> of a script event handler the appropriate ScriptEngine.ARGV entry gets supplied, allowing the script
>> to fetch the event object directly as an argument.
>> As I have signed the OCA the code (in form of a git diff) can be directly applied to FXMLLoader.java.
>> If you need the patch in a different form, then please advise.
>> ---rony

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