Problems with Java Scripting API

Question

Hello Everyone!
Guys, I need help with Java scripting API. A problem is that I cannot understand how can I operate Java Object's fields and methods from the script language. I have chosen embedded javascript to work with. And I can get the fields and methods of in-box java classes (such as ArrayList for example), but I cannot work with methods and fields from my own classes!
Here is an example:
public class ScriptingExample {  
    class MyClass {  
        int myfield = 5;  
        int getInt() {return 7;}  
    public void runExample() {  
        ScriptEngineManager mgr = new ScriptEngineManager();  
        List<ScriptEngineFactory> factories = mgr.getEngineFactories();  
        ScriptEngineManager factory = new ScriptEngineManager();  
        ScriptEngine engine = factory.getEngineByName("JavaScript");  
        MyClass mc = new MyClass();  
        try{  
            engine.put("mc", mc);  
            engine.eval("print(mc.myfield); print(mc.getInt())"); // or engine.eval("print(mc.myfield)");
        } catch (Exception e) {e.printStackTrace();}  
}  If I run the code with the commented part it prints "undefined" instead of "5".
If I run the code as it is it prints error instead of "7":
undefinedjavax.script.ScriptException: sun.org.mozilla.javascript.internal.EcmaError: TypeError: Cannot find function getInt. (<Unknown source>#1) in <Unknown source> at line number 1
at com.sun.script.javascript.RhinoScriptEngine.eval(Unknown Source)
at com.sun.script.javascript.RhinoScriptEngine.eval(Unknown Source)
at javax.script.AbstractScriptEngine.eval(Unknown Source)
at solutiondatabase.ScriptingExample.runExample(ScriptingExample.java:26)
at solutiondatabase.Main.main(Main.java:49)
How can I fix it?

Answer 1

Guys,
please let me raise this topic because several new questions emerged.
(1) How can I get all the variables created inside my engine?
There are two kinds of variables: first kind is Java obejcts put inside the engine and second kind is the variables created in my script, such as 'var a = 4;'. How can I list all the variables of that two kinds?
(2) Is there is a way to make 'import static' to the engine? I dont want to write MyClass.MyEnum.MyEnumItem every time. Also, I cannot put the whole enum into the engine with engine.put("MyEnum", MyEnum); I can put only enum items separately: engine.put("MyEnum", MyEnum.EnumItemA);. Thats why I ask about static import.
(3) How can I cast engine variables back to java variables inside my java code?
Here is my example:
package mypackage;
import java.util.ArrayList;
import java.util.List;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;
public class Main
     public static void main(String[] args) throws Exception 
          ScriptEngineManager mgr = new ScriptEngineManager();
          List<ScriptEngineFactory> factories = mgr.getEngineFactories();
          ScriptEngineManager factory = new ScriptEngineManager();
          ScriptEngine engine = factory.getEngineByName("JavaScript");
          ArrayList<Double> myList = new ArrayList<Double>();
          myList.add(5.0);                    
          engine.put("MyList", myList);     
          engine.eval("MyVar = MyList.get(0);");
          System.out.println((Double)engine.get("MyVar"));
}The result is:
Exception in thread "main" java.lang.ClassCastException: sun.org.mozilla.javascript.internal.NativeJavaObject cannot be cast to java.lang.Double
+     at mypackage.Main.main(Main.java:28)+
Is it possible to retrieve my Double java object from the engine?
Edited by: Dmitry_MSK on Aug 6, 2010 1:56 AM