Evaluate a script file

With this example we are going to demonstrate how to evaluate a simple script file in Java. We are using the ScriptEngine interface that provides methods for the basic scripting functionality. In short, to evaluate a script file you should:

  • Create a new ScriptEngineManager. The ScriptEngineManager implements a discovery and instantiation mechanism for ScriptEngine classes and also maintains a collection of key/value pairs storing state shared by all engines created by the Manager.
  • Use the getEngineByName(String shortName) method to look up and create a ScriptEngine for a given name.
  • Create an instance of File object that points to the scripting file.
  • Create a FileReader to read the file.
  • Use the eval(Reader reader) method to execute the script provided by the Reader.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;

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

public class EvaluateScriptExample {
    public static void main(String[] args) {

  // Obtain JavaScript Engine

  ScriptEngineManager manager = new ScriptEngineManager();

  ScriptEngine engine = manager.getEngineByName("ECMAScript");

  try {

  	//Create an instance of File object that point to scripting file

File script = new File("sample.js");

//create a FileReader to read the file to be passed to the ScriptEngine.eval() method.

Reader reader = new FileReader(script);


  } catch (FileNotFoundException e) {


  } catch (ScriptException e) {



This was an example of how to evaluate a simple script file in Java.

Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.
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