FXMLLoader: not supplying filename to script engine, not supplying event object as argument to script
Rony G. Flatscher
Rony.Flatscher at wu.ac.at
Wed Nov 13 15:21:47 UTC 2019
On 13.11.2019 15:40, Michael Paus wrote:
> 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
Thank you very much for this pointer, will read and try to follow the procedures outlined there!
> 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
>> 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
>> 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"
>> 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
>> 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
>> So looking for interested committers who would be willing to mentor this patch. Please advise.
>> 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
>>> to eval() the script code:
>>> * ScriptEngine.FILENAME
>>> o This value denotes the file name from where the script code was fetched that is being
>>> 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
>>> 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
>>> 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
>>> If you need the patch in a different form, then please advise.
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