Re: [Jython-users] Fwd: Re: Eclipse + Jython = Call Python from Java does not work

[Philipp Z. <ze...@gm...>]

On 11/09/2011 04:18 PM, er...@fr... wrote:
>
> Philipp, I feel your pain.  The Jython object factories are a PITA 
> when used from Eclipse.  I could not get them to work no matter what I 
> tried.  The debugger kept showing me what appeared to be a bug in the 
> jython guts, but I couldn't fix it.  So try this.  This works for me.
>
> The first snippet is just to show you how to invoke it from 
> java/eclipse.  The two functions at the bottom are just support 
> functions we use to find scripts in our plugins and set up the engine 
> to use them.  The use of ScriptEngine is because we use the Java 
> embedded scripting support to find the Jython engine.
>
> Good luck!
>
>
> -Eric
>
>     org.osi.framework.Bundle bundle = MyPlugin.getDefault().getBundle();
>     File scriptPath = JythonExecutor.getJythonScript(bundle, "/", 
> "MyPyScript.py"); //search bundle from the top
>     javax.script.ScriptEngine engine = 
> createJythonEngine(scriptPath.getParent());
>     assert engine != null;
>
>     try {
>         engine.eval("import MyPyScript");
>         engine.eval("myBuilding = MyPyScript.myFunction()");
>         IBuilding myBuilding = (IBuilding) engine.get("myBuilding");
>         myBuilding.doSomething();
>     }
>     catch(Throwable t) {...}
>
>     ...
>
>
>
>     /**
>      * Gets an instance of a jython engine.
>      * @param pathEntries [optional] absolute pathnames (to 
> directories only)
>      *        to put into the engine's sys.path (where are your scripts?)
>      * @return an initialized intance of a jython engine, or 
> <em>null</em> if it can't be constructed
>      */
>     @Nullable
>     public static javax.script.ScriptEngine 
> createJythonEngine(String... pathEntries) {
>         setupJythonHomePointer();
>         PySystemState state = new PySystemState();
>         for (String pathEntry : pathEntries) {
>             state.path.append(Py.newString(pathEntry));
>         }
>         Py.setSystemState(state);
>         ClassLoader loader = EftPlugin.class.getClassLoader();
>         ScriptEngineManager engineManager = new 
> ScriptEngineManager(loader);
>         return engineManager.getEngineByName("python");
>     }
>
>     /**
>      * Gets the pathname to a bundled script
>      * @param bundle     your eclipse plugin's Bundle
>      * @param startingLocation
>      * @param scriptName the file you're hunting for
>      * @return a File instance pointing to the script you ask for, or 
> <em>null</em> if it can't be found
>      */
>     @SuppressWarnings({"unchecked"})
>     @Nullable
>     public static File getJythonScript(Bundle bundle, String 
> startingLocation, String scriptName) {
>         File file = null;
>         String location = bundle.getLocation();
>         String needsPrefix = location.split("@", 2)[1];
>         String installPath = System.getProperty(
>                 "osgi.install.area") //eg. file:/c:/eftinstall
>                 .split("file:/")[1];
>
>         Enumeration<URL> entries = 
> bundle.findEntries(startingLocation, scriptName, true);
>         if (entries != null) {
>             URL url = entries.nextElement();
>             String s = String.format("%s/%s/%s)",
>                     installPath,    // c:/eftinstall
>                     needsPrefix,    // path to plugin
>                     url.getPath()); // path to script
>
>             try {
>                 file = new File(s).getCanonicalFile();
>             }
>             catch (IOException e) {
>                 logger.debug(e);
>                 e.printStackTrace();
>             }
>         }
>         return file;
>     }
>
Hi Eric,

thanks for this solution! actually it is far more than i requested and 
also expected, but it's totally what i need, as my next goal was to use 
python from inside eclipse plugins, so again, thanks a lot for your 
answer. The only questions that remain at first sight are

- what does setupJythonHomePointer(); and
- what needs to be done that the class cast works (to IBuilding) as I 
currently get ClassCastException related errors (i.e.: pytzhon objects 
cannot be casted into java ones, although they implement the interface)?

thanks a lot for your help!

cheers,

philipp