sun.org.mozilla.javascript.internal.NativeJavaObject cannot be cast to java.lang.String

Question

I'm using java 6 javax.script feature but I have an issue :

Before I call the ScriptEngine.eval() method I put some attributes to the ScriptContext:

scriptContext.setAttribute("Utils", utils, ScriptContext.ENGINE_SCOPE);

In the script I call :

var s = utils.getMyString()

The Java getMyString() method returns a String (java.lang.String).

The type of 's' in the scriptContext is sun.org.mozilla.javascript.internal.NativeJavaObject that wrap the Java String instance.

When I try to get the attribute from the context in Java with:

(String) scriptContext.getAttribute("s");

I got

    java.lang.ClassCastException:
 sun.org.mozilla.javascript.internal.NativeJavaObject cannot be cast to java.lang.String

When I write in the script:

var s = "hello world"

or

var s = "" + utils.getMyString()

or

var s = String(utils.getMyString())

all is well because these are javascript Strings that can be get from the scriptContext thanks to an internal conversion.

I think that NativeJavaObjects should be unwrapped (see sun.org.mozilla.javascript.internal.Wrapper.unwrap()) when they are released from the scriptContext.

So, is it a bug ? I have the same issue with java7u5.

I don't beleive that I would have to do :

var s = String(utils.getMyString())

to convert a Java String to a JavaScript String to be able to get it back as a Java String...

Thanks for your point of view.

The problem occurs for Strings. If getMyString() returns MyString instance It works. So why this issue for methods returning Strings ??? — kiki
– kiki, Commented Jul 18, 2012 at 13:38

Community · Accepted Answer · 2017-05-23 11:52:09Z

1

The problem seems to be similar to: https://stackoverflow.com/questions/11814010/javascript-rhino-java-float-method-returns-number-or-object and Rhino Javascript: How to convert Object to a Javascript primitive?

but in your case I beleive that:

Context.enter().getWrapFactory().setJavaPrimitiveWrap(false);

will throw NullPointerException. You use Rhino from JDK javax.script, and ScriptEngine.eval methods wrapps all operations handling context (enter, exit context etc), so if you invoke above-mentioned code before eval, rhino context may not be initialized (enter method assign context to current Thread).

Solution may be to use Rhino directly form org.mozilla and handling context directly: link and invoke above code when enter a context.

I had similar problem (and others as well) when i used JDKs ScriptEngine and i solved it using Rhino form mozilla.

edited May 23, 2017 at 11:52

CommunityBot

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answered Sep 6, 2012 at 23:01

Dominik Kunicki

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