Evaluate Javascript functions on JSON data in Java

README.md

Java8 is required.

With a method defined as:

private Object evaluate(String jsonDocument, String javascriptFunction) {
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
    try {
        String script = "var fun = function(document) {\n" +
                "    return JSON.parse(document)." + javascriptFunction + ";\n" +
                "};";
        System.out.println(script); // debug
        engine.eval(script);
        Invocable invocable = (Invocable) engine;

        return invocable.invokeFunction("fun", jsonDocument);
    } catch (ScriptException | NoSuchMethodException e) {
        throw new RuntimeException(e);
    }
}

It is simple to access and manipulate nested properties with a Javascript expression:

String document = new Scanner(this.getClass().getClassLoader().getResourceAsStream("sample.json"), "UTF-8").useDelimiter("\\A").next();

Object result = evaluate(document, "menu.id");
// String[file]

// Javascript functions are available
result = evaluate(document, "menu.popup.menuitem.map(function (item) {return item.value;})");
// ScriptObjectMirror(Array)[New, Open, Close]

// Nashorn Function Literals
result = evaluate(document, "menu.popup.menuitem.map(function (item) item.value)");
// ScriptObjectMirror(Array)[New, Open, Close]

sample.json

{"menu": {
  "id": "file",
  "value": "File",
  "popup": {
    "menuitem": [
      {"value": "New", "onclick": "CreateNewDoc()"},
      {"value": "Open", "onclick": "OpenDoc()"},
      {"value": "Close", "onclick": "CloseDoc()"}
    ]
  }
}}