Is this possible for use javascript to call a java

Question

The java have a script manager that allow java calling javascript, like this:

import javax.script.*;
public class ExecuteScript {
 public static void main(String[] args) throws Exception {
 // create a script engine manager
 ScriptEngineManager factory = new ScriptEngineManager();
 // create a JavaScript engine
 ScriptEngine engine = factory.getEngineByName("JavaScript");
 // evaluate JavaScript code from String
 engine.eval("print('Welocme to java world')");
 }

 public static void sayHi(){
   System.out.println("hihi");
 }
}

My question is, if I have a sayHi() function, can I use the javascript, via the script engine to call the Java function? Thanks.

Answer 1

Here is a tiny example with Java 8 Nashorn that works as a stand-alone script without any packages:

import javax.script.*;
import java.util.LinkedList;

public class RunJavaFromJs {
  public static void main(String[] args) throws Exception {
    LinkedList<Integer> jList = new LinkedList<>();
    jList.add((Integer)42);

    ScriptEngine engine = 
      (new ScriptEngineManager())
      .getEngineByName("nashorn");
    Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
    bindings.put("jList", jList);
    engine.eval("" + 
      "load('nashorn:mozilla_compat.js');\n" +
      "// call static method\n" + 
      "var i = Packages.RunJavaFromJs.helloWorld(42);\n" + 
      "// perform side effect\n" + 
      "print('Result was: ' + i + '(printed from JS)');\n" + 
      "// call method on `jList` instance passed in bindings \n" +
      "jList.add(12345);\n" +
      "print(jList.toString());"
    );
  }
  public static int helloWorld(int x) {
    System.out.println("Hello, world! (printed from Java in static method)");
    return x * x;
  }
}

If you just save it in RunJavaFromJs.java, then compile and run using

javac RunJavaFromJs.java && java RunJavaFromJs

then you obtain:

Hello, world! (printed from Java in static method)
Result was: 1764(printed from JS)
[42, 12345]

Answer 2

The following snippet

package org.test.script;
import javax.script.*;

public class ExecuteScript {
    public static void main(String[] args) throws Exception {
        // create a script engine manager
        ScriptEngineManager factory = new ScriptEngineManager();
        // create a JavaScript engine
        ScriptEngine engine = factory.getEngineByName("JavaScript");
        // evaluate JavaScript code from String
        engine.eval("" +
            "importPackage(org.test.script);\n" +
            "print('Welocme to java world\\n');\n" +
            "ExecuteScript.sayHi();");
    }

    public static void sayHi() {
        System.out.println("hihi");
    }
}

outputs

Welocme to java world
hihi

Answer 3

Quickly hacked together from the JavaDocs.

import javax.script.*;

public class ExecuteScript {

    public static void main(String[] args) throws Exception {
        // create a Java object
        ExecuteScript es = new ExecuteScript();

        // create a script engine manager
        ScriptEngineManager factory = new ScriptEngineManager();
        // create a JavaScript engine
        ScriptEngine engine = factory.getEngineByName("JavaScript");
        // evaluate JavaScript code from String
        engine.eval("println('Welcome to Java world')");

        // add the Java object into the engine.
        engine.put("es",es);

        ScriptEngineFactory sef = engine.getFactory();
        String s = sef.getMethodCallSyntax("es", "sayHi", new String[0]);
        // show the correct way to call the Java method
        System.out.println(s);
        engine.eval(s);
    }

    public static void sayHi(){
        System.out.println("hihi");
    }
}

Output

Welcome to Java world
es.sayHi()
hihi
Press any key to continue . . .

Answer 4

I'm not sure what script manager you are using but with Rhino you can do things like

var date = new java.util.Date();
print(date);

So with your example you should be able to call it like a static method:

ExecuteScript.sayHi();