javascript - Nashorn 绑定(bind)问题

标签 javascript java nashorn

我有一个像下面这样的java类

    public class StaticBean {

        public static String returnString(int num){
            String json = "[{\"name\" : \"John Doe\", \"age\" : 30}]";
            return json;
        }

    }

在下面的测试中，我有两个引擎实例。

执行后，我发现无法将绑定(bind)实例复制到另一个实例上并将其用于在同一引擎或不同引擎中执行。即使我复制了，结果也与我使用相同引擎/绑定(bind)得到的结果不匹配。 

@Test
    public void testParsingStringObjects() {

        Bindings b = engine.createBindings();
        b.put("ndb", getBindingObject(StaticBean.class, engine));

        engine.setBindings(b, ScriptContext.ENGINE_SCOPE);


        String source = "print('Definition in engine instance 1');" 

                + "var SysU = {};\n"

                + "SysU.returnObject = function returnObjectJS(){\n" 

                + "var string = ndb.returnString(1);\n"

                + "return JSON.parse(string);\n" + "}\n"

                + "SysU.returnString = function returnStringJS(){\n" 

                + "var string = ndb.returnString(1);\n"

                + "print('String returned by the java function SysU.returnString() '+string);\n" 

                + "return string;\n" + "};\n"

                + "print('====================Using the same engine instance for execution====================');\n"

                + "(function (){" + "var json = {};\n"

                + "print(\"String Returned in Caller SysU.returnString(): \"+SysU.returnString());\n"

                + "print(\"Object Returned in Caller SysU.returnObject(): \"+SysU.returnObject());\n"

                + "print(\"**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): \"+JSON.stringify(SysU.returnObject()));\n"

                + "print('Adding the object in another ( json.ext = SysU.returnObject();) ...');\n" 

                + "json.ext = SysU.returnObject();\n"

                + "print(\"Added JSON object which is stringified to display JSON.stringify(json): \"+JSON.stringify(json));\n" + "})();";


        try {
            engine.eval(source);

            Bindings oldEngineBindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
            Bindings localBindings = engine2.getBindings(ScriptContext.ENGINE_SCOPE);
            Bindings newBindings = engine.createBindings();

            oldEngineBindings.put("fileName","oldEngine");
            localBindings.put("fileName","localEngine");


            newBindings.putAll(oldEngineBindings);
            newBindings.putAll(localBindings);

            oldEngineBindings.putAll(localBindings);

            ScriptContext ctxt = new SimpleScriptContext();
            ctxt.setBindings(oldEngineBindings, ScriptContext.ENGINE_SCOPE);

            engine.setContext(ctxt);

            engine.eval(""
                    + "print('====================Using the same engine with original binding ====================');\n"
                    + "(function (){" + "var json = {};\n"

                    + "print(\"String Returned in Caller SysU.returnString(): \"+SysU.returnString());\n"

                    + "print(\"Object Returned in Caller SysU.returnObject(): \"+SysU.returnObject());\n"

                    + "print(\"**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): \"+JSON.stringify(SysU.returnObject()));\n"

                    + "print('Adding the object in another ( json.ext = SysU.returnObject();) ...');\n" 

                    + "json.ext = SysU.returnObject();\n"

                    + "print(\"Added JSON object which is stringified to display JSON.stringify(json): \"+JSON.stringify(json));\n" + "})();");

            ctxt.setBindings(newBindings, ScriptContext.ENGINE_SCOPE);

            engine.setContext(ctxt);

            engine.eval(""
                    + "print('====================Using the same engine with copied new binding ====================');\n"
                    + "(function (){" + "var json = {};\n"

                    + "print(\"String Returned in Caller SysU.returnString(): \"+SysU.returnString());\n"

                    + "print(\"Object Returned in Caller SysU.returnObject(): \"+SysU.returnObject());\n"

                    + "print(\"**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): \"+JSON.stringify(SysU.returnObject()));\n"

                    + "print('Adding the object in another ( json.ext = SysU.returnObject();) ...');\n" 

                    + "json.ext = SysU.returnObject();\n"

                    + "print(\"Added JSON object which is stringified to display JSON.stringify(json): \"+JSON.stringify(json));\n" + "})();",newBindings);

            ctxt.setBindings(oldEngineBindings, ScriptContext.ENGINE_SCOPE);

            engine2.setContext(ctxt);

            engine2.eval(""
                    + "print('====================Using a different engine instance with original binding ====================');\n"
                    + "(function (){" + "var json = {};\n"

                    + "print(\"String Returned in Caller SysU.returnString(): \"+SysU.returnString());\n"

                    + "print(\"Object Returned in Caller SysU.returnObject(): \"+SysU.returnObject());\n"

                    + "print(\"**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): \"+JSON.stringify(SysU.returnObject()));\n"

                    + "print('Adding the object in another ( json.ext = SysU.returnObject();) ...');\n" 

                    + "json.ext = SysU.returnObject();\n"

                    + "print(\"Added JSON object which is stringified to display JSON.stringify(json): \"+JSON.stringify(json));\n" + "})();");

        } catch (ScriptException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


    }

这是一种可接受的行为吗？还是错误？我应该能够复制绑定(bind)并在同一引擎或不同引擎实例的不同范围内使用它们并产生相同的结果。

我在 Java8u101 上测试

运行测试时的结果。 当绑定(bind)或引擎实例更改时，ReturnObject() 函数似乎会失败。

Definition in engine instance 1
====================Using the same engine instance for execution====================
String returned by the java function SysU.returnString() [{"name" : "John Doe", "age" : 30}]
String Returned in Caller SysU.returnString(): [{"name" : "John Doe", "age" : 30}]
Object Returned in Caller SysU.returnObject(): [object Object]
**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): [{"name":"John Doe","age":30}]
Adding the object in another ( json.ext = SysU.returnObject();) ...
Added JSON object which is stringified to display JSON.stringify(json): {"ext":[{"name":"John Doe","age":30}]}
====================Using the same engine with original binding ====================
String returned by the java function SysU.returnString() [{"name" : "John Doe", "age" : 30}]
String Returned in Caller SysU.returnString(): [{"name" : "John Doe", "age" : 30}]
Object Returned in Caller SysU.returnObject(): [object Object]
**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): [{"name":"John Doe","age":30}]
Adding the object in another ( json.ext = SysU.returnObject();) ...
Added JSON object which is stringified to display JSON.stringify(json): {"ext":[{"name":"John Doe","age":30}]}
====================Using the same engine with copied new binding ====================
String returned by the java function SysU.returnString() [{"name" : "John Doe", "age" : 30}]
String Returned in Caller SysU.returnString(): [{"name" : "John Doe", "age" : 30}]
Object Returned in Caller SysU.returnObject(): [object Object]
**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): undefined
Adding the object in another ( json.ext = SysU.returnObject();) ...
Added JSON object which is stringified to display JSON.stringify(json): {}
====================Using a different engine instance with original binding ====================
String returned by the java function SysU.returnString() [{"name" : "John Doe", "age" : 30}]
String Returned in Caller SysU.returnString(): [{"name" : "John Doe", "age" : 30}]
Object Returned in Caller SysU.returnObject(): [object Object]
**Stringified Object Returned in Caller JSON.stringify(SysU.returnObject()): undefined
Adding the object in another ( json.ext = SysU.returnObject();) ...
Added JSON object which is stringified to display JSON.stringify(json): {}

编辑:-

找到这个线程 https://bugs.openjdk.java.net/browse/JDK-8067642 .这提到了一些关于外部对象是 ScriptObjectMirror 实例的事情。我使用 typeof 运算符来显示在失败和成功的情况下返回的对象类型，并且两次都是 ScriptObjectMirror 但如果我在上下文中使用原始绑定(bind)对象，则 stringify 会按预期工作。

编辑 2:-

添加了一个非常简单的测试来演示以上内容。有点像上面的 TLDR :)。执行下面的代码表明绑定(bind)对象上的 putAll() 没有像我们预期的那样工作。 

@Test
    public void testParsingObjects() throws ScriptException {

        String source = "var Func = {};\n"
                + "Func.getJavaScriptObject = function(){"
                + "var jsString = '{\"foo\":\"bar\"}';\n"
                + "return JSON.parse(jsString);"
                + "};";


        String executor = "(function(){ "
                + "var obj = Func.getJavaScriptObject();"
                + "print(JSON.stringify(obj));"
                            + " })();";

        System.out.println("Executing source...");
        engine.eval(source);
        System.out.println("\nUsing the same binding instance and engine\n");
        engine.eval(executor);

        Bindings originalBinding = engine.getBindings(ScriptContext.ENGINE_SCOPE);


        Bindings copiedBinding = engine.createBindings();

        copiedBinding.putAll(originalBinding);

        System.out.println("\nUsing the copied binding instance and engine\n");
        engine.eval(executor,copiedBinding);


    }

执行结果。

Executing source...

Using the same binding instance and engine

{"foo":"bar"}

Using the copied binding instance and engine

undefined

最佳答案

这是我在不同线程使用的 ScriptContext 实例之间使用共享编译的 JavaScript 代码的代码。这里的主要好处是只编译一次代码，尽管我也受益于不需要多次从 REST API 流式传输代码。为简洁起见，我没有包括 REST 部分。

import javax.script.CompiledScript; 
import javax.script.ScriptContext; 
import javax.script.ScriptEngine; 
import javax.script.ScriptEngineManager; 
import javax.script.ScriptException; 
import javax.script.SimpleScriptContext; 
import java.util.concurrent.Callable; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.Future; 
import java.util.concurrent.ExecutionException; 
import java.util.ArrayList; 
import java.util.List; 

public class ContextDemo {
    static CompiledScript codeLib; 
    static ScriptEngine engine; 
    static ScriptContext context; 
    static List <Future<String>> taskResults; 
    static ExecutorService executor; 
    static List <Callable<String>> tasks = new ArrayList<Callable<String>> (); 

    public static void main(String[] args) {
        try {
            // Initialize workers and execute
            run(4); 
        } catch(InterruptedException | ExecutionException | ScriptException e) {
            System.out.println(e.getMessage()); 
        }
    }

    static void run(int workers) throws InterruptedException, ExecutionException, ScriptException {
        // Initialize engine and initial context
        engine = new ScriptEngineManager().getEngineByName("nashorn"); 
        context = new SimpleScriptContext(); 
        engine.setContext(context); 
        // Compile a JavaScript object with a function
        codeLib = ((javax.script.Compilable)engine).compile("var lib = { func1: function(n, s) { return 'thread number ' + n + ': ' + s; } };"); 
        // Create executor with specified number of workers
        executor = Executors.newFixedThreadPool((int)workers); 
        for (int i = 0; i < workers; i++) {
            tasks.add(workerLambda(i)); 
        }
        // Invoke worker pool
        taskResults = executor.invokeAll(tasks); 
        // Iterate futures list and report results
        for (int i = 0; i < workers; i++) {
            Future < String > f = taskResults.get(i); 
            if (f.isDone()) {
                System.out.println(f.get()); 
            } else {
                System.out.println("Thread " + i + " not done"); 
            }
        }
        // Shutdown the executor
        executor.shutdown(); 
    }

    static Callable <String> workerLambda(int n) {
        int workerNum = n; 
        // Thread-specific script context initialization
        SimpleScriptContext threadContext = new SimpleScriptContext(); 
        threadContext.setBindings(engine.createBindings(), ScriptContext.ENGINE_SCOPE); 
        try {
            // Inject compiled code library into thread-specific ScriptContext
            codeLib.eval(threadContext); 
        } catch (ScriptException e1) {
            System.out.println(e1.getMessage()); 
        }
        // Return the lambda
        return () ->  {
            // Call the injected object method and return the result
            return (String)engine.eval("lib.func1(" + workerNum + ", 'Hello!');", threadContext); 
        }; 
    }
}

这个输出:

thread number 0: Hello!
thread number 1: Hello!
thread number 2: Hello!
thread number 3: Hello!

关于javascript - Nashorn 绑定(bind)问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38862075/

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