java - 为 Nashorn 脚本引擎定义默认/全局 Java 对象？

Question

借助 Java 的 Nashorn 脚本引擎，我可以使用如下绑定(bind)在 eval() 的上下文中提供对象:

Bindings bindings = scriptContext.getBindings(ScriptContext.ENGINE_SCOPE);
bindings.put("rules", myObj); 
scriptEngine.eval("rules.someMethod('Hello')", scriptContext);

我希望能够通过提供默认对象来简化 javascript，这样 javascript 就不是:

rules.someMethod('Hello')

我可以写:

someMethod('Hello')

有什么办法可以实现吗？ (someMethod 是对象上的方法，不是静态方法)

Answer 1

您可以使用 nashorn 的 Object.bindProperties 扩展将任意对象的属性绑定(bind)到 JS 全局对象。这样用户就可以从脚本中调用您的“默认”对象的方法(和访问属性)而无需限定。请在此处查看 Object.bindProperties 文档 https://wiki.openjdk.java.net/display/Nashorn/Nashorn+extensions#Nashornextensions-Object.bindProperties

示例代码:

import javax.script.*;

public class Main {
   public static void main(String[] args) throws Exception {
       ScriptEngineManager m = new ScriptEngineManager();
       ScriptEngine e = m.getEngineByName("nashorn");

       // get JavaScript "global" object
       Object global = e.eval("this");
       // get JS "Object" constructor object
       Object jsObject = e.eval("Object");

       Invocable invocable = (Invocable)e;

       // calling Object.bindProperties(global, "hello");
       // which will "bind" properties of "hello" String object
       // to JS global object
       invocable.invokeMethod(jsObject, "bindProperties", global, "hello");

       // you're calling "hello".toUpperCase()"
       e.eval("print(toUpperCase())");
       // accessing bean property "empty" on 'hello' object
       e.eval("print(empty)");

       // just print all (enumerable) properties of global
       // you'll see methods, properties of String class
       // (which'd be called on "hello" instance when accessed)
       e.eval("for (var i in this) print(i)");
   }
}