Nashorn: Javascript to Java call question

Fri Jun 7 12:03:37 PDT 2013

Thanks Sundar, Jim for the explanation.

I extracted the jsobjectTest() from ScriptEngineTest.java as it is and
compiled and ran it, when I run it I still get the same error that I got
with my example. I have put all of this in a gist to demonstrate what I was
doing:
https://gist.github.com/neomatrix369/5731520

I also ran the ScriptEngineTest using the jtreg command and that ran
successfully:

 ~/jtreg/linux/bin/jtreg -jdk:/usr/lib/jdk1.8.0
-Xbootclasspath/p:$HOME/sources/jdk8_tl/nashorn/dist/nashorn.jar
-verbose:fail test/src/jdk/nashorn/api/scripting/ScriptEngineTest.java

Regards,
mani

On Thu, Jun 6, 2013 at 11:25 AM, Mani Sarkar <sadhak001 at gmail.com> wrote:

> Hi Jim,
>
> You have been very quick with your response to my query.
>
> Thanks for going through the trouble, apologies for the empty folders,
> they are submodules that haven;t been pushed correctly to my repo.
>
> I have made the changes you suggested and rebuilt my class (I had to get
> the latest version of the codebase as JSObject wasn;t present in
> nashorn.jar in  my old code-base).
>
> After building and running I get the below:
>
> Exception in thread "main" java.lang.ClassCastException:
> jdk.nashorn.api.scripting.ScriptObjectMirror cannot be cast to
> jdk.nashorn.api.scripting.JSObject
> at JSJSONInJava.main(JSJSONInJava.java:19)
>
> Lines 18 and 19 are as follows:
> 17: // fetch the value of a variable
> 18: Object objFromJS = engine.get("JSONObjectUsingJavaScript");
> 19: JSObject jsonObjFromJS = (JSObject) objFromJS;
>
> Any ideas, or is it something new?
>
> Regards,
> mani
>
>
> On Wed, Jun 5, 2013 at 8:51 PM, Jim Laskey <james.laskey at oracle.com>wrote:
>
>> The repo you provided has empty JSON-java and JSON-js directories, so
>> I'll give you an alternative example.  The main thing to note is that,
>> because of a JS object's dynamic nature, it can not mirror a Java object.
>>  A better analogy would be to think of a JS object as a Map object, where
>> properties are keys and you access values with keys.
>>
>> Run the enclosed example as follows;
>>
>> javac Example.java
>> java Example
>>
>> The class of myObject is a JSObject.  You can access properties of a
>> JSObject with getMember/setMember (or getSlot/setSlot for integer keys.)
>>
>> === Example.java ===
>>
>> import javax.script.*;
>> import jdk.nashorn.api.scripting.JSObject;
>>
>> public class Example {
>> public static void main(String[] args) throws Exception {
>>  ScriptEngineManager factory = new ScriptEngineManager();
>>  ScriptEngine engine = factory.getEngineByName("nashorn");
>>  engine.eval(new java.io.FileReader("Example1.js"));
>>  JSObject myObject = (JSObject)engine.get("myObject");
>>  System.out.println(myObject.getMember("a"));
>>  System.out.println(myObject.getMember("b"));
>>  System.out.println(myObject.getMember("c"));
>>         myObject.setMember("d", "A new string");
>>  engine.eval(new java.io.FileReader("Example2.js"));
>>
>> }
>> }
>>
>> === Example1.js ===
>>
>> var myObject = {
>>    a: "A string",
>>    b: 100,
>>    c: true
>> }
>>
>> === Example2.js ===
>>
>> print(myObject.d);
>>
>> ==== Output ===
>>
>> A string
>> 100
>> true
>> A new string
>>
>>
>> Cheers,
>>
>> -- Jim
>>
>>
>>
>>
>>
>>
>> On 2013-06-05, at 3:50 PM, Mani Sarkar <sadhak001 at gmail.com> wrote:
>>
>> Hi,
>>
>> I have another query regarding the example (see
>>
>> https://github.com/neomatrix369/NashornHackDay/blob/master/examples/JSON_in_JS_and_Java/JSJSONInJava.java
>> )
>> created sometime back  during the Nashorn hackday. When I bring a JS
>> object
>> created in Nashorn into Java I'm not able to access the object directly,
>> how do I access it like a normal java object.
>>
>> If its a raw / primitive type then the contents are accessible (you can
>> see
>> the value) while for JS object, when I say
>>
>> *System.out.println(JSObjectFromNashorn);*
>>
>>
>> I get the below output
>>
>> *[object object]*
>>
>>
>> The full implementation of what I'm talking about can be found at the
>> above
>> link.
>>
>> Regards,
>> mani
>>
>> --
>> *Twitter:* @theNeomatrix369          *Blog:*
>> http://neomatrix369.wordpress.com
>> *JUG activity:* LJC Advocate (@adoptopenjdk & @adoptajsr programs)
>> *Meet-a-Project:* https://github.com/MutabilityDetector
>> *Bitbucket:* https://bitbucket.org/neomatrix369  * **Github:*
>> https://github
>> .com/neomatrix369
>> *LinkedIn:* http://uk.linkedin.com/pub/mani-sarkar/71/a77/39b
>> *Devoxx UK 2013* was a grand success:
>> http://www.devoxx.com/display/UK13/Home
>>
>> *Don't chase success, rather aim for "Excellence", and success will come
>> chasing after you!*
>>
>>
>>
>
>
> --
> *Twitter:* @theNeomatrix369          *Blog:*
> http://neomatrix369.wordpress.com
> *JUG activity:* LJC Advocate (@adoptopenjdk & @adoptajsr programs)
> *Meet-a-Project:* https://github.com/MutabilityDetector
> *Bitbucket:* https://bitbucket.org/neomatrix369  * **Github:* https://
> github.com/neomatrix369
> *LinkedIn:* http://uk.linkedin.com/pub/mani-sarkar/71/a77/39b
> *Devoxx UK 2013* was a grand success:
> http://www.devoxx.com/display/UK13/Home
>
> *Don't chase success, rather aim for "Excellence", and success will come
> chasing after you!*
>

-- 
*Twitter:* @theNeomatrix369          *Blog:*
http://neomatrix369.wordpress.com
*JUG activity:* LJC Advocate (@adoptopenjdk & @adoptajsr programs)
*Meet-a-Project:* https://github.com/MutabilityDetector
*Bitbucket:* https://bitbucket.org/neomatrix369  * **Github:* https://github
.com/neomatrix369
*LinkedIn:* http://uk.linkedin.com/pub/mani-sarkar/71/a77/39b
*Devoxx UK 2013* was a grand success:
http://www.devoxx.com/display/UK13/Home

*Don't chase success, rather aim for "Excellence", and success will come
chasing after you!*