为Nashorn脚本引擎定义默认/全局Java对象？

使用Java的Nashorn脚本引擎,我可以使用如下所示的绑定在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,以便代替javascript：

rules.someMethod('Hello')

我可以写：

someMethod('Hello')

有没有办法实现这个目标？ (someMethod是对象的方法,而不是静态方法)

解决方法:

您可以使用nashorn的Object.bindProperties扩展将任意对象的属性绑定到JS全局对象.这样,用户可以无需限定地从脚本调用“默认”对象上的方法(和访问属性).
请参阅此处的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)");
   }
}

标签：java,nashorn
来源： https://codeday.me/bug/20190724/1527452.html