Scripting in Java Tutorial - Scripting in Java Parameters

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The Java Scripting API allows us to pass parameters from Java application to the script engine and vice versa.

Passing Parameters from Java Code to Scripts

msg is a variable used in the print() function.

The script does not declare the msg variable.

We can pass a parameter to a script engine in several ways.

One way is to use the put(String paramName, Object paramValue) method of the script engine, which accepts two arguments:

• the name of the parameter, which needs to match the name of the variable in the script.
• the value of the parameter.

To pass a parameter named msg to the script engine, call the put() method as follows:

engine.put("msg", "Hello from Java program");

The following code shows how to pass Parameters From a Java Program to Scripts.

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
//w  ww  . j av a2s . c  o  m
public class Main {
  public static void main(String[] args) {
    // Get the Nashorn engine
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    String script = "print(msg)";
    try {
      engine.put("msg", "Hello from Java program");
      engine.eval(script);
    } catch (ScriptException e) {
      e.printStackTrace();
    }
  }
}

The code above generates the following result.

To pass a parameter named msg to a script in JRuby.

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("jruby");

String script = "puts($msg)";
engine.put("msg", "Hello from Java");

// Execute the script
engine.eval(script);

Example

Properties and methods of Java objects passed to scripts can be accessed in scripts

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
/*from w ww . j a  va  2 s .c  o m*/
public class Main {
  public static void main(String[] args) throws Exception{
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    String script = "print(msg.toUpperCase());print(msg.indexOf('a'))";
    engine.put("msg", "java2s.com");
    engine.eval(script);
  }
}

The code above generates the following result.

Passing Parameters from Scripts to Java Code

A script engine can pass global scope variables to Java code.

The get(String variableName) method from ScriptEngine can access those variables in Java code.

It returns a Java Object.

The declaration of a global variable is scripting-language-dependent.

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
/*  ww  w .  j av  a  2s  .co m*/
public class Main {
  public static void main(String[] args) throws Exception {
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("JavaScript");

    String script = "var year = 2015";

    engine.eval(script);
    Object year = engine.get("year");
    System.out.println("year's class:" + year.getClass().getName());
    System.out.println("year's value:" + year);
  }
}

The code above generates the following result.

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