How can I get javascript array output in java (in array)?

Question

I have a javascript file fun.js

function fun1(){
    var arr =['This','is','from','js'];
    return arr;
}

I want to get this array in java array so I used nashorn as-

try{
    ScriptEngine engine= new ScriptEngineManager().getEngineByName("nashorn");
    engine.eval(new FileReader("fun.js"));
    Invocable invocable = (Invocable) engine;
    Object obj = (Object)invocable.invokeFunction("fun1");
    System.out.println(obj.toString());
}
catch(Exception e){
    e.printStackTrace();
}

But I am getting this output- [object Array]

How can I get this output as java array?

eval() is one of the worst things you could ever do in any language. — ICanKindOfCode
– ICanKindOfCode, Commented Mar 25, 2018 at 6:01
Did you try looping through the array and printing out the contents? — ICanKindOfCode
– ICanKindOfCode, Commented Mar 25, 2018 at 6:04
@Prashant It gives error as -- java.lang.ClassCastException: jdk.nashorn.api.scripting.ScriptObjectMirror cannot be cast to [Ljava.lang.Object; — Rahul Choubey
– Rahul Choubey, Commented Mar 25, 2018 at 7:26
what is the content of your file fun.js. Also please show the code of method fun1 — Harshita Sethi
– Harshita Sethi, Commented Mar 25, 2018 at 11:56

MANOJ · Accepted Answer · 2018-03-25 11:58:03Z

public static void main(String[] args) throws JSONException, FileNotFoundException, ScriptException, NoSuchMethodException {

        ScriptEngine engine= new ScriptEngineManager().getEngineByName("nashorn");

        engine.eval(new FileReader("C:\\Users\\Niku\\eclipse-workspace\\java_sample\\src\\test.js"));

        Invocable invocable = (Invocable) engine;
        Object obj = (Object)invocable.invokeFunction("fun1");
        Gson gson = new Gson();
        String k = gson.toJson(obj);
        JSONObject o = new JSONObject(k);
        System.out.println(o.getString("0"));
        System.out.println(o.getString("1"));
        System.out.println(o.getString("2"));
        System.out.println(o.getString("3"));

        Iterator x = o.keys();
        JSONArray jsonArray = new JSONArray();
        ArrayList<String> ar = new ArrayList<String>();
        while (x.hasNext()){
            String key = (String) x.next();
            ar.add(o.get(key).toString());
            jsonArray.put(o.get(key));
        }

        System.out.println(ar);
}

Iterating through the JsonObject can get you each element which can be added to another array to be used.

A. Sundararajan · Accepted Answer · 2018-03-26 03:07:45Z

You can use methods of Nashorn specific extension object "Java" to convert between JavaScript and Java arrays.

See also: https://wiki.openjdk.java.net/display/Nashorn/Nashorn+extensions#Nashornextensions-java_to

Simple Example that invokes Java.to from Java code:

import javax.script.*;

public class Main {
    public static void main(String[] args) throws Exception {
        ScriptEngine e = new ScriptEngineManager().getEngineByName("nashorn");
        e.eval("function fun1() { return ['this', 'is', 'from', 'js']; }");
        Invocable invocable = (Invocable)e;
        Object obj = (Object)invocable.invokeFunction("fun1");
        // get "Java" api object
        Object Java = e.get("Java");
        // invoke Java.to function to convert JS array to Java String array
        String[] arr = (String[])invocable.invokeMethod(
            Java, "to", obj, "java.lang.String[]");
        // access String array
        for (String s : arr) { System.out.println(s); }
    }
}

Ameya Pandilwar · Accepted Answer · 2018-03-25 06:23:16Z

0

The invokeFunction returns an instance of JSObject [jdk.nashorn.api.scripting.JSObject]

You could assign the response to a JSObject and then iterate over the values -

JSObject jsObject = null;
try {
    jsObject = (JSObject) invocable.invokeFunction("fun1");
    for (Object object : jsObject.values()) {
        System.out.println(object);
    }
} catch (NoSuchMethodException e) {
    ...
}

answered Mar 25, 2018 at 6:23

Ameya Pandilwar

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1 Comment

Ameya Pandilwar Over a year ago

Make sure that the import for the JSObject is jdk.nashorn.api.scripting.JSObject

ElSheikh · Accepted Answer · 2018-03-25 11:48:14Z

0

I have tried recreating the scenario in java alone and was able to print the contents.

public class test {
    public static void main(String[] args) {
        String[] a = {"This","is","from","js"};
        Object obj = (Object) a;
        String stringArray = Arrays.deepToString((Object[]) obj);
        System.out.println(stringArray);
        String [] b =  stringArray.replaceAll("[\\[\\]]", "").split(",");
        System.out.println(b[0]);   
    }
}

edited Mar 25, 2018 at 11:48

ElSheikh

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answered Mar 25, 2018 at 9:02

MANOJ

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1 Comment

Rahul Choubey Over a year ago

But in this case it gives this error-- java.lang.ClassCastException: jdk.nashorn.api.scripting.ScriptObjectMirror cannot be cast to [Ljava.lang.Object;

ElSheikh · Accepted Answer · 2018-03-25 12:26:58Z

0

The output what you'll get in Java will be in JsonArray format. So you can pass your input content in jsonArray and iterate over that JsonArray.

you can use jettison-1.3.jar as JSONAray library.

Here's what you can try.

String[] outputStr = new String[jsonArray.length()];
try {
    JSONArray jsonArray = new JSONArray(invocable.invokeFunction("fun1"));
    for (int i = 0; i < jsonArray.length(); i++) {
        outputStr[i] = jsonArray.getString(i);
    }
} catch(JSONException ex) {
    ex.printStackTrace();
}

For using org.json.simple.JSONArray import, you can use the following code

    String[] outputStr = new String[jsonArray.length()];
    try{
        JSONParser parser = new JSONParser();
        JSONArray jsonArray = (JSONArray) parser.parse(invocable.invokeFunction("fun1");

        for (int i = 0; i < jsonArray.size(); i++) {
            outputStr[i] = (String) jsonArray.get(i);
        }
    } catch(JSONException ex) {
        ex.printStackTrace();
    }

edited Mar 25, 2018 at 12:26

ElSheikh

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answered Mar 25, 2018 at 8:24

Harshita Sethi

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5 Comments

Rahul Choubey Over a year ago

Can I use this code in java program directly.I tried this with jettison-1.3.jar but it gives error .I import following-- import org.json.simple.JSONObject; import org.json.simple.JSONArray;

Harshita Sethi Over a year ago

with jettison jar, your import will be org.codehaus.jettison.json.JSONArray. Yes you can use this code directly in Java program

Rahul Choubey Over a year ago

It gives this error when using jettison.jar- no suitable constructor found for JSONArray(Object) constructor JSONArray.JSONArray(JSONTokener) is not applicable (argument mismatch; Object cannot be converted to JSONTokener) and 3 more like this....

Rahul Choubey Over a year ago

While using 2nd code I got follwing 2 error no suitable method found for parse(Object) JSONArray jsonArray = (JSONArray) parser.parse(invocable.invokeFunction("fun1")); method JSONParser.parse(String) is not applicable (argument mismatch; Object cannot be converted to String) error: cannot find symbol method length()

Rahul Choubey Over a year ago

Thanks for your effort madam I got the answer.

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