Call external javascript functions from java code

Question

By using Java Scripting API, I am able to execute JavaScript within Java. However, can someone please explain what I would need to add to this code in order to be able to call on functions that are in C:/Scripts/Jsfunctions.js

import javax.script.*;

public class InvokeScriptFunction {
public static void main(String[] args) throws Exception {
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    // JavaScript code in a String
    String script1 = "function hello(name) {print ('Hello, ' + name);}";
    String script2 = "function getValue(a,b) { if (a===\"Number\") return 1; 
                     else return b;}";
    // evaluate script
    engine.eval(script1);
    engine.eval(script2);

    Invocable inv = (Invocable) engine;

    inv.invokeFunction("hello", "Scripting!!");  //This one works.      
 }
}

user432 · Accepted Answer · 2014-04-04T07:45:49.140

60

Use ScriptEngine.eval(java.io.Reader) to read the script

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");
// read script file
engine.eval(Files.newBufferedReader(Paths.get("C:/Scripts/Jsfunctions.js"), StandardCharsets.UTF_8));

Invocable inv = (Invocable) engine;
// call function from script file
inv.invokeFunction("yourFunction", "param");

edited Apr 04 '14 at 07:45

answered Apr 04 '14 at 07:40

user432

3,506
17
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2

Yes, it's useful, thanks. How can we use Window in the provided javascript since through java code there will be no browser for this. – sandeep kale Feb 06 '15 at 17:23
Which window or browser are you referring to? – MRK187 May 13 '15 at 14:02
what was the solution? – Fahim Oct 14 '15 at 00:22
2

In case difficulties in loading relative path use below code. `URL fileUrl = getClass().getResource("js/WebWorker.js"); engine.eval(Files.newBufferedReader(Paths.get(fileUrl.toURI()),StandardCharsets.UTF_8));` – Mano Oct 28 '15 at 09:08
Hi, I have doubt, I have tried to invoke the function which has dependencies of moment.js library. So i just added the library script as well with that like this `engine.eval(Files.newBufferedReader(Paths.get("/Volumes/Bala/Eclipse Mars/Workspace/ClientWebAccessFullHistory/war/js/Library/Moment.js"), StandardCharsets.UTF_8)); engine.eval(Files.newBufferedReader(Paths.get("/Volumes/Bala/Eclipse Mars/Workspace/ClientWebAccessFullHistory/war/js/newLayout/FullHistory/fullHistory.js"), StandardCharsets.UTF_8));` But it is not available at global scope. – Bala.Raj May 06 '16 at 15:24
@Bala.Raj you can try with `load('path/to/Mom‌ent.js');` inside your script. – Ben Dec 16 '16 at 23:48

score 2 · Answer 2 · answered Jan 01 '18 at 19:05

try {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");
        System.out.println("okay1");
        FileInputStream fileInputStream = new FileInputStream("C:/Users/Kushan/eclipse-workspace/sureson.lk/src/main/webapp/js/back_end_response.js");
        System.out.println("okay2");
        if (fileInputStream != null){
         BufferedReader reader = new BufferedReader(new InputStreamReader(fileInputStream));
         engine.eval(reader);
         System.out.println("okay3");
        // Invocable javascriptEngine = null;
         System.out.println("okay4");
        Invocable invocableEngine = (Invocable)engine;
         System.out.println("okay5");
         int x=0;
         System.out.println("invocableEngine is : "+invocableEngine);
         Object object = invocableEngine.invokeFunction("backend_message",x);

         System.out.println("okay6");
        }
        }catch(Exception e) {
            System.out.println("erroe when calling js function"+ e);
        }

Thank you for this code snippet, which might provide some limited, immediate help. A [proper explanation would greatly improve its long-term value](//meta.stackexchange.com/q/114762/206345) by showing _why_ this is a good solution to the problem, and would make it more useful to future readers with other, similar questions. Please [edit] your answer to add some explanation, including the assumptions you've made. — Mogsdad, Jan 01 '18 at 19:10

score 1 · Answer 3 · answered May 10 '18 at 17:41

Let us say your jsfunctions.js file has a function "display" and this file is stored in C:/Scripts/Jsfunctions.js

jsfunctions.js

var display = function(name) {
print("Hello, I am a Javascript display function",name);
return "display function return"
}

Now, in your java code, I would recommend you to use Java8 Nashorn. In your java class,

import java.io.FileNotFoundException;
import java.io.FileReader;

import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

class Test {
public void runDisplay() {
ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
try {
  engine.eval(new FileReader("C:/Scripts/Jsfunctions.js"));
  Invocable invocable = (Invocable) engine;
  Object result;
  result = invocable.invokeFunction("display", helloWorld);
  System.out.println(result);
  System.out.println(result.getClass());
  } catch (FileNotFoundException | NoSuchMethodException | ScriptException e) {
    e.printStackTrace();
    }
  }
}

Note: Get the absolute path of your javascript file and replace in FileReader() and run the java code. It should work.

FYI...for those who have moved to OpenJDK, because of Oracle's Java licensing changes or for whatever reason, Nashorn is deprecated in OpenJDK. https://openjdk.java.net/jeps/335 — HankNessip, Oct 31 '19 at 16:09

Call external javascript functions from java code

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