How to Use the GWT-RequestFactory in Android SyncAdapter (always getting ValidationTool-Error)

Question

I got a question about the usage of GWT-RequestFactory in Android. As a starting point I used the code from the “Create a AppEngine connected Android-Project”-Wizard (infos: http://code.google.com/intl/de-DE/eclipse/docs/appengine_connected_android.html) and it worked great.

But now in my case I want do extend this application to use a local ContentProvider with SQLite and a SyncService with SyncAdapter do synchronize the data from the ContentProvider to the AppEngine using the RequestFactory. Now my problem is the following: I can call

MyRequestFactory requestFactory = Util.getRequestFactory(mContext, MyRequestFactory.class);

in any Activity I want and will receive an instance of MyRequestFactory. (Note: Util is a class created by the Wizard.) But if I try to make the same call from my SyncAdapter, I will get a java.lang.RuntimeException: The RequestFactory ValidationTool must be run for the com.hotool.client.MyRequestFactory RequestFactory type”.

Maybe for your information: The Util.getRequestFacory method looks like this:

/**
* Creates and returns an initialized {@link RequestFactory} of the given
* type.
 */
public static <T extends RequestFactory> T getRequestFactory(
        Context context, Class<T> factoryClass) {

    T requestFactory = RequestFactorySource.create(factoryClass);

    SharedPreferences prefs = getSharedPreferences(context);
    String authCookie = prefs.getString(Util.AUTH_COOKIE, null);

    String uriString = Util.getBaseUrl(context) + RF_METHOD;
    URI uri;
    try {
        uri = new URI(uriString);
    } catch (URISyntaxException e) {
        Log.w(TAG, "Bad URI: " + uriString, e);
        return null;
    }
    requestFactory.initialize(new SimpleEventBus(),
            new AndroidRequestTransport(uri, authCookie));

    return requestFactory;
}

The error occurs in RequestFactorySource which lies in the requestfactory-client.jar I think, that this may be a Class-Loader problem, but tried to figure it out with no success.

I tried to use the ValidationTool but first of all it didn't help and secondly I discovered, that the classes the ValidationTool will generate are already in place (probably thanks to annotation-processing as mentioned here: http://code.google.com/p/google-web-toolkit/wiki/RequestFactoryInterfaceValidation)

Does anybody have an idea what could cause this?

Thanks a lot and best regards.

Markus Neuenschwander

Answer 1

You are right Mark, this is an class-loader issue.

It happens in the requestfactory-client.jar, here the relevant source:

class InProcessRequestFactory extends AbstractRequestFactory {

    //...

    public InProcessRequestFactory(Class<? extends RequestFactory> requestFactoryInterface) {
        this.requestFactoryInterface = requestFactoryInterface;
        deobfuscator =
            Deobfuscator.Builder.load(requestFactoryInterface,
                Thread.currentThread().getContextClassLoader()).build();
    }

    //...

}

and

public class Deobfuscator {

    //...

    public static class Builder {
        public static Builder load(Class<?> clazz, ClassLoader resolveClassesWith) {
            Throwable ex;
            try {
                Class<?> found;
                try {
                    // Used by the server
                    found = Class.forName(clazz.getName() + GENERATED_SUFFIX, false, resolveClassesWith);
                } catch (ClassNotFoundException ignored) {
                    // Used by JRE-only clients
                    found = Class.forName(clazz.getName() + GENERATED_SUFFIX_LITE, false, resolveClassesWith);
                }
                Class<? extends Builder> builderClass = found.asSubclass(Builder.class);
                Builder builder = builderClass.newInstance();
                return builder;
            } catch (ClassNotFoundException e) {
                throw new RuntimeException("The RequestFactory ValidationTool must be run for the "
                    + clazz.getCanonicalName() + " RequestFactory type");
            } catch (InstantiationException e) {
            ex = e;
        } catch (IllegalAccessException e) {
            ex = e;
        }
        throw new RuntimeException(ex);
    }

    //...

}

The problem is that Thread.currentThread().getContextClassLoader() seems to return a null value when called from the sync adapter on Android, because the Sync Adapter thread is created by the System, not by your application.

I solved this by calling manually calling setContextClassLoader in the onPerformSync method before creating a requestfactory instance:

@Override
public void onPerformSync(final Account account, Bundle extras,
        String authority, final ContentProviderClient provider,
        final SyncResult syncResult) {

    Thread.currentThread().setContextClassLoader(mContext.getClassLoader());

    // ...

    MyRequestFactory requestFactory = Util.getRequestFactory(mContext,
            MyRequestFactory.class, acsidToken);

    // ...
}

I hope this makes sense. Andreas