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POHow to use Rhino to bridge a Java class that contains overloaded methods and is indexable in JavaScript?
 

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  1. POHow to use Rhino to bridge a Java class that contains overloaded methods and is indexable in JavaScript?
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    <p>In porting a C# project to Java that uses JavaScript for user scripts, there's a class that has an overloaded method:</p> <pre><code>public class TreeNode { public TreeNode GetChild(int index) { ... } public TreeNode GetChild(String childName) { ... } public TreeNode GetChild(String targetAttributeName, String targetAttributeValue) { ... } ... } </code></pre> <p>Using Rhino, I can bridge this object between Java and JavaScript with:</p> <pre><code>ScriptableObject.putProperty(scope, "TreeNode", Context.javaToJS(new TreeNode(), scope)); </code></pre> <p>This works great for scripts that simply make calls to the functions (and all the overloaded functions get resolved to the correct type correctly). However, the C# application also indexes into the TreeNode. For example, a JavaScript user function is:</p> <pre><code>function NumericButtonClick() { screen = TreeNode.FindNodeById("Screen"); screen["Text"] = screen["Text"] + Source["Text"]; } </code></pre> <p>Running this JavaScript code results in the expected <code>Exception in thread "AWT-EventQueue-0" org.mozilla.javascript.EvaluatorException: Java class "TreeNode" has no public instance field or method named "Text".</code></p> <hr> <p>To fix this, Rhino supports this by allowing you implement the <code>Scriptable</code> interface (or extend the <code>ScriptableObject</code> which contains a bunch of common boilerplate code). After doing that, the binding seemingly disappears:</p> <pre><code>Exception in thread "AWT-EventQueue-0" org.mozilla.javascript.EcmaError: TypeError: Cannot find default value for object. </code></pre> <p>Debugging the code, the specific interaction is that Rhino makes four calls to the <code>get()</code> method of <code>Scriptable</code>:</p> <pre><code>get(name = "FindNodeByID") get(name = "__noSuckMethod__") get(name = "toString") get(name = "valueOf") </code></pre> <hr> <p>To fix this, we can create specific <code>FunctionObject</code> objects to let Rhino know FindNodeByID is a function to some piece of Java code. (While I've tried doing it manually, just using <code>Scriptable.defineFunctionProperties</code> does this automatically in a lot less code.) This works well until we reach the overloaded GetChild functions, when we get this exception:</p> <pre><code>org.mozilla.javascript.EvaluatorException: Method "GetChild" occurs multiple times in class "TreeNode". </code></pre> <p>Alternatively, <code>ScriptableObject.defineClass(scope, TreeNode.class)</code> will map <code>jsFunction_*</code> functions into JaavScript. However, this generates the same sort of error:</p> <pre><code>org.mozilla.javascript.EvaluatorException: Invalid method "jsFunction_GetChild": name "GetChild" is already in use. </code></pre> <p>Finally, I looked at adding logic inside the <code>get()</code> to try and pick which <code>FunctionObject</code> we want and return in to Rhino. However, you're not provided any parametrization of the function or any way to look forward except in a very hacky, cumbersome way. </p> <hr> <p>Am I missing something? Is there any way to both index into a mapped Java object in Rhino and have overloaded Java functions? Rhino clearly supports them both, and surely supports them together, but it doesn't seem obvious how to do it.</p> <p>Thanks for any ideas!</p>
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