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About Byron Kiourtzoglou

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.

Access Java Object from a script

In this example we shall show you how to access a Java Object from a script. We are using the ScriptEngine interface that provides methods for the basic scripting functionality. To access a Java Object from a script one should perform the following steps:

  • 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 getEngineByExtension(String extension) API method to look up and create a ScriptEngine for the js extension.
  • Use put(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 brands, with the key "brandArray".
  • Create a new String script to print the elements in the list.
  • Use the eval(String script) method to execute the script,
  • as described in the code snippet below.  

    package com.javacodegeeks.snippets.core;
    
    import javax.script.ScriptEngineManager;
    import javax.script.ScriptEngine;
    import javax.script.ScriptException;
     
    public class AccessJavaObjectFromScript {
        public static void main(String[] args) {
    
      
    
      // Create an array of car brands
    
      String[] brands = {"Audi", "Mercedes", "Renault", "Ford", "Seat"};
     
    
      // Script that reads the values of the array that contains string of car brands.
    
      String script =
    
    
        "var index; " +
    
    
        "var brands = brandsArray; " +
    
    
        " " +
    
    
        "for (index in brands) { " +
    
    
        "    println(brands[index]); " +
    
    
        "}" ;
     
    
      // Obtain a ScriptEngine instance.
    
      ScriptEngineManager manager = new ScriptEngineManager();
    
      ScriptEngine engine = manager.getEngineByExtension("js");
     
    
      // Place the brands array into the engine using brandsArray key.
    
      engine.put("brandsArray", brands);
     
    
      try {
    
    
    engine.eval(script);
    
      } catch (ScriptException e) {
    
    
    e.printStackTrace();
    
      }
        }
    }
    

    Output:

    Audi
    Mercedes
    Renault
    Ford
    Seat
    

      
    This was an example of how to access a Java Object from a script in Java.

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