CODEWITHSUNDEEP
javajavascriptrhino
wanderlust
wanderlust

Reputation: 31

Sharing java objects in Rhino Javascript

Let me first start with admitting that I am a noob in JavaScript. So the question might not be very sound at the basics and might lack enough information to help me.

Background

My organisation has an internal Eclipse based IDE for JavaScript. All we have to do is write scripts in JavaScript and directly execute them. My guess is it uses Rhino since I have seen it in the stack trace of some exceptions.

My code runs across 3 ".js" files.

Script-1: Declare global variables and instantiate them as Java objects

importClass(java.util.HashMap);
var hmTCResult = new HashMap();

Script-2: Perform some actions using the global variables from Script-1

Script-2.prototype.run = function() {
hmTCResult.put("Result", "Fail");
};

changeStatus = function(strStatus){
hmTCResult.put("Result", strStatus);
};

Script-3: Call function in Script-2 which uses the global variables

changeStatus("Pass")

Problem Definition

When from Script-3 I call the function in Script-2 it doesn't seem pick the instance variables and my function fails i.e. I get an exception "hmTCResult not set to the instance of an object." Please note that the the same variable hmTCResult works well in Script 1.

I have done some reading of the Scope and the Context in JavaScript but haven't been able to break through it, since I don't see it explicitly in the IDE.

I will be happy to provide more information if needed.

Upvotes: 3

Views: 3373

Answers (3)

Georg
Georg

Reputation: 1007

This works fine, just juggle your scopes and get prototype search set up:

Context cx = Context.enter();
try {
    // Cache and reuse:
    ScriptableObject sealedSharedScope = cx.initStandardObjects(null,
            true);
    // Force the LiveConnect stuff to be loaded.
    String loadMe = "RegExp; getClass; java; Packages; JavaAdapter;";
    cx.evaluateString(sealedSharedScope, loadMe, "preLoadLazyLoad", 0,
            null);

    cx.evaluateString(sealedSharedScope, "varInRoot = 'blah';",
            "setVarInRoot", 0, null);

    // here you can put more cx.evaluateString calls to set up your
    // environment (eg. hmTCResult)

    // now connect a throw-away new scope into the hierarchy, with local
    // vars:
    Scriptable scope = cx.newObject(sealedSharedScope);
    // ensure that definitions in the root scope are found
    scope.setPrototype(sealedSharedScope);
    // ensure that new global variables are created in this scope (don't
    // use
    // var for them!)
    scope.setParentScope(null);

    cx.evaluateString(scope, "localVar = varInRoot;", "mySource", 0,
            null);
    assertEquals("blah", scope.get("localVar", scope).toString());
    // new var not in root:
    assertEquals(ScriptableObject.NOT_FOUND,
            sealedSharedScope.get("localVar", scope));
} finally {
    Context.exit();
}

Beware that scope.get doesn't search the prototype chain - gotta do that yourself!

Scopes are independent of Context and survive Context.exit().

Upvotes: 1

David P. Caldwell
David P. Caldwell

Reputation: 3829

My guess, without more information, and assuming your modified transcripts are absolutely correct, is that your scripts are being run in separate scopes, all with the global scope as a parent.

As such, my guess is that the reason changeStatus works in the third script is because there is no var declaration for it. Thus, absent other configuration, this will be defined as a variable in the top-level, or global, scope, that is shared across the three scripts.

My guess is that the reason hmTCResult does not work is that it is declared with the keyword var, indicating a local variable. If all scripts were running in the top-level scope, this would define a variable on the global object. But if each script runs in its own scope, this would define a variable only in the scope of script 1. You wouldn't see the problem in the scope of script 2, because no one is executing the code in script 2 until script 3 executes.

Upvotes: 0

Aubin
Aubin

Reputation: 14853

To evaluate a js script in Java the following operation may be performed

ScriptEngine engine = new ScriptEngineManager().getEngineByMimeType( "text/javascript" );
Bindings bindings = engine.getBindings( ScriptContext.GLOBAL_SCOPE );
bindings.put( "varname", ... );
bindings.put( ... );
engine.put( ScriptEngine.FILENAME, script.toString());
engine.eval( new FileReader( script ));

If the 3 scripts are loaded within the same engine/bindings it's ok, but if the engine is newly allocated for executing script3, the context has been cleared.

This post is not really an answer but too long to be a comment.

Upvotes: 0

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