java对象的GraalJs调用构造函数

Question

我想使用graal js为我的应用程序提供一些脚本扩展。

如何在javascript端初始化一个新的java对象？

Context ctx = Context ctx = Context.newBuilder().allowHostAccess(HostAccess.ALL).allowAllAccess(true).build().create();
Value binding = ctx.getBindings("js");
binding.putMember("ArrayList", ArrayList.class);
ctx.eval("js","let list = new ArrayList();list.add(\"1\")");
List list = binding.getMember("list").as(List.class);
assert list.size() == 1;

下面的代码引发异常

Exception in thread "main" TypeError: instantiate on JavaClass[java.util.ArrayList] failed due to: Message not supported.
    at <js> :program(Unnamed:1:13-27)
    at org.graalvm.polyglot.Context.eval(Context.java:371)

运行graalvm-ce-java11 11 19.3.2

Answer 1

您需要使用Java.type。

下面是从https://www.graalvm.org/docs/reference-manual/polyglot/获取的一个示例

var array = new (Java.type("int[]"))(4);
array[2] = 42;
console.log(array[2])

下面是一个用GraalVM 20.0.0测试的完全可运行的示例

import org.graalvm.polyglot.*;

class M {
    public static void main(String[] args) {
        try (Context context = Context.newBuilder().allowAllAccess(true).build()) {
            java.util.ArrayList v = context.eval("js",
            "var ArrayList = Java.type('java.util.ArrayList');" +
            "var list = new ArrayList();" + 
            "list.add(1); list").asHostObject();
            System.out.println(v.get(0));
            assert v.get(0).equals(1);
        }
    }
}

同跑

graalvm-ce-java8-20.0.0/bin/javac M.java 
graalvm-ce-java8-20.0.0/bin/java -ea M

以获得1作为输出。

Answer 2

您还可以使用sj4js库。在这里，您可以定义构造函数，这些构造函数可以无缝地融入JS。

// we create a new JS engine and add
// TestClass as a constructor. This constructor is added to globalThis such that it
// can be called as a costructor.
try (JScriptEngine engine = new JScriptEngine(new JsGlobalThis(),"gt")) {
    engine.addConstructor(new TestClass("empty"));
            
    /* call your js code here */
}

你的JS代码看起来像这样，你会料到的。

// we create a new variable from the constructor
var tc = new TestClass("test");

console.log(tc.name)
// test