How can I access Java String methods from a String variable passed to JavaScript ?

Question

I'm using the Java Scripting Engine (in Java 1.6) to dynamically evaluate some expressions in my Java program. I can pass my Java objects from Java to JavaScript, and call their methods, but this stops working correctly when I pass String objects.

For example, in my Java I can define a class, JavaClass, with a doSomething method. I can then call the doSomething method when I pass a JavaClass object to JavaSCript.

However, if I make a String object in Java, and pass it to JavaScript, I get an error when I try to call the endsWith method on it, in JavaScript.

My code is as follows :-

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");
String myString = "apple hello";
JavaClass javaClass = new JavaClass();
engine.put("myString", myString);
engine.put("thing", javaClass);
engine.eval("thing.doSomething()");
engine.eval("myString.endsWith(\"hello\")");

The doSomething method is called correctly, but it can't find endsWith :-

__EXCEPTION__:javax.script.ScriptException:   sun.org.mozilla.javascript.internal.EcmaError: TypeError: Cannot find function endsWith. 

It's as if my Java String object gets converted to a JavaScript string object - I can use the length property of a JavaScript String, for instance.

I can add my own endsWith function to my JavaClass class, which simply calls the String endsWith, and this works correctly - but is not nice... :(

If it is being converted, can I stop this happening ? If it's something else, am I doing something wrong ? Is there a way to fix it ?

Thanks ! :)

Answer 1

Change the last line to this. By default Strings are converted between Java and JS types automatically. Hence, you must forcefully convert myString into a Java string within your JS code..

    engine.eval("new java.lang.String(myString).endsWith(\"hello\")");