With this example we are going to demonstrate how to modify a Java object in script. In short, to modify a Java object using script we have followed the steps below:

• Create a newScriptEngineManager. 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 thegetEngineByExtension(String extension) API method to look up and create aScriptEngine for the js extension.
• Useput(String key, Object value) API method of ScriptEngine to set a key/value pair in the state of the ScriptEngine that may either create a Java Language Binding to be used in the execution of scripts or be used in some other way, depending on whether the key is reserved. The value set here is a list of String car names, with the key"brandList".
• Create a new String script to print the list and then add new elements in the list.
• Use theeval(String script) method to execute the script.
• After executing the script print the list elements again. The list now has the new elements added to it by the script.

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; import javax.script.ScriptEngineManager;import javax.script.ScriptEngine;import javax.script.ScriptException;import java.util.Date;import java.util.List;import java.util.ArrayList; public class ModifyObjectFromScript {    public static void main(String[] args) {  // Create a List of car brands  List<String> brands = new ArrayList<String>();  brands.add("Audi");  brands.add("Mercedes");  brands.add("Renault");  brands.add("Ford");  brands.add("Seat");  // Obtain a ScriptEngine instance  ScriptEngineManager manager = new ScriptEngineManager();  ScriptEngine engine = manager.getEngineByExtension("js");   // Set List into the engine  engine.put("brandList", brands);  try {engine.eval(getScript());// Redisplay the modified version of brands list object.for (String brand : brands) {    System.out.println("Brand = " + brand);}  } catch (ScriptException e) {e.printStackTrace();  }    }     private static String getScript() {    // Script that reads and adds brands   String script =    "var index; " +    "var brands = brandList.toArray(); " +    " " +    "for (index in brands) { " +    "    println(brands[index]); " +    "}" +    " " +    "brandList.add("BMW"); " +    "brandList.add("KIA"); " +    "brandList.add("Smart"); ";  return script;    }}

Output:

AudiMercedesRenaultFordSeatBrand = AudiBrand = MercedesBrand = RenaultBrand = FordBrand = SeatBrand = BMWBrand = KIABrand = Smart

  
This was an example of how to modify a Java object in script in Java.

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