Nashorn - JS引擎

 Nashorn是在java中高效動態執行JS代碼的運行環境。

ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        engine.eval("print('hello');"); // execute js from source
        File f = new File("resources/scripts.js");
        engine.eval(new FileReader(f)); // execute js from file

調用JS

　　首先把需要調用的js代碼保存為scripts.js:

function add(a, b) {
    return a + b;
}

var f1 = function(name) {
    print("JS: " + name);
    return "Greeting from JS";
}
var f2 = function(obj) {
    print("JS Class: " + Object.prototype.toString.call(obj));
}

    Java中調用：

        ScriptEngine engine = new ScriptEngineManager()
                .getEngineByName("nashorn");
        engine.eval("print('hello');"); // execute js from source
        File f = new File("resources/scripts.js");
        engine.eval(new FileReader(f)); // execute js from file
        Invocable invocable = (Invocable) engine;
        Object sum = invocable.invokeFunction("add", 1, 2);
        System.out.println(sum);
        invocable.invokeFunction("f2", new Date());
        invocable.invokeFunction("f2", LocalDateTime.now());            

由於js中的代碼在jvm中是原生態調用，類型不會丟失。

調用Java

　　Java方法必須是public。否則調用的時候找不到：

    public static String greeting(String name) {
        System.out.println("From Java " + name);
        return "From Java";
    }

    public static void getCls(Object obj) {
        System.out.println(obj.getClass());
    }

     ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
     File f = new File("resources/scripts.js");
     engine.eval(new FileReader(f)); // execute js from file

　　JS代碼：

var cls = Java.type("nashorn.NashornTest");
print(cls.greeting('Zhijie'));

    原始JS類型可以轉換成適當的Java包裝類。原生JS對象表示成內部適配類。

　　

cls.getCls(123);
//class java.lang.Integer

cls.getCls(49.99);
//class java.lang.Double

cls.getCls(true);
//class java.lang.Boolean

cls.getCls("hi there")
//class java.lang.String

cls.getCls(new Number(23));
//class jdk.nashorn.internal.objects.NativeNumber

cls.getCls(new Date());
//class jdk.nashorn.internal.objects.NativeDate

cls.getCls(new RegExp());
//class jdk.nashorn.internal.objects.NativeRegExp

cls.getCls({foo: 'bar'});
//class jdk.nashorn.internal.scripts.JO4

ScriptObjectMirror

jdk.nashorn.api.scripting.ScriptObjectMirror是JS對象在Java中的映射。這個類實現了Map接口。

    
    public static void f(ScriptObjectMirror mirror) {
        System.out.println(mirror.getClassName() + ": " +
            Arrays.toString(mirror.getOwnKeys(true)));
    }
    
    public static void callMethodOfJSObject(ScriptObjectMirror person) {
        System.out.println("Full Name is: " + person.callMember("getFullName"));
    }

cls.f({a:'a',b:'b'});

function Person(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.getFullName = function() {
        return this.firstName + " " + this.lastName;
    }
}

var person1 = new Person("Zhijie", "Liu");
cls.callMethodOfJSObject(person1);

 Nashorn擴展了ECMAScript 5:

• Typed Arrays

• Collections and For Each

• Lambda expressions and Streams

• Extending classes

• Parameter overloading

• Java Beans

• Function Literals

• Binding properties

• Trimming strings

• Whereis

• Import Scopes

• Convert arrays

• Calling Super

• Loading scripts

可以進一步閱讀http://winterbe.com/posts/2014/04/05/java8-nashorn-tutorial/