lugar - Llama a funciones javascript externas desde código java.

javascript caracteristicas

Question

Al usar Java Scripting API, puedo ejecutar JavaScript dentro de Java. Sin embargo, ¿puede alguien explicar qué necesitaría agregar a este código para poder llamar a las funciones que están en 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 = (String)"function hello(name) {print (''Hello, '' + name);}";
    String script2 = (String)"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.      
 }
}

Answer 1

Digamos que su archivo jsfunctions.js tiene una función "mostrar" y este archivo se almacena en C: /Scripts/Jsfunctions.js

jsfunctions.js

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

Ahora, en tu código java, te recomendaría que uses Java8 Nashorn. En tu clase de java,

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();
    }
  }
}

Nota: Obtenga la ruta de acceso absoluta de su archivo javascript y reemplácelo en FileReader () y ejecute el código java. Deberia de funcionar.

Answer 2

Use ScriptEngine.eval(java.io.Reader) para leer el 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");

Answer 3

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);
        }