Nashorn: Javascript to Java call question

Sun Jun 9 03:30:38 PDT 2013

Hi guys,

I have resolved the earlier error that I reported, I thought I was using
the correct jdk but then I wasn't and switching to the latest version of
the OpenJDK (nashorn) source and then bootstrapping to the image created by
the build process fixed it (hinted by you) - thanks for that.

I'm now able to access the member elements, returned by Javascript through
the JSObject. Although the JSON I created also contained an array of string
elements, which I wasn't able to access but got [object Array] when I
printed it to console.

I tried casting it to org.json.JSONArray but it was of no use. Then I came
across the link
http://cr.openjdk.java.net/~hannesw/8007060/webrev.01/src/jdk/nashorn/internal/objects/NativeFunction.java.html,
and applying the checks on the object to see if it can be converted or not
I got the output:
function.apply.expects.array (didn't pass any of the checks, and terminated
at the last else).

Is there a JSONArray object within the nashorn package that I could use? Do
you have any other example for that?

Thanks.

Regards.
Mani

On Fri, Jun 7, 2013 at 8:03 PM, Mani Sarkar <sadhak001 at gmail.com> wrote:

> 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!*
>

-- 
*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!*