Jersey Client on Android - NullPointerException

Question

I am trying to create a simple Android client for a web service I have built, but something goes wrong at runtime.

Here is the Client:

public class M         


        

Answer 1

Paul's suggestion is correct. I got a little bit deeper in that subject and found a reason.

Android apk packaging tool (APKBuilder class from sdklib.jar) ignores different folders while it creates the package (source). One of those folders is META-INF - no matter if its in the attached library or in the project's source folder.

Workaround for version 1.8 (and probably other also, but I didn't test it) of Jersey is to provide custom (default one looks up META-INF/services/ which is not present in android apk) implementation for ServiceFinder$ServiceIteratorProvider which has hard coded provider class names. I based my implementation on this implementation proposed by Lucas:

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;

import android.util.Log;

import com.sun.jersey.spi.service.ServiceFinder.ServiceIteratorProvider;

public class AndroidServiceIteratorProvider extends ServiceIteratorProvider {

    private static final String TAG = AndroidServiceIteratorProvider.class.getSimpleName();
    private static final String MESSAGE = "Unable to load provider";

    private static final HashMap SERVICES = new HashMap();

    private static final String[] com_sun_jersey_spi_HeaderDelegateProvider = {
            "com.sun.jersey.core.impl.provider.header.MediaTypeProvider",
            "com.sun.jersey.core.impl.provider.header.StringProvider"
    };

    private static final String[] com_sun_jersey_spi_inject_InjectableProvider = { 
    };

    private static final String[] javax_ws_rs_ext_MessageBodyReader = {
            "com.sun.jersey.core.impl.provider.entity.StringProvider",
            "com.sun.jersey.core.impl.provider.entity.ReaderProvider"
    };

    private static final String[] javax_ws_rs_ext_MessageBodyWriter = {
            "com.sun.jersey.core.impl.provider.entity.StringProvider",
            "com.sun.jersey.core.impl.provider.entity.ReaderProvider"
    };

    static {
        SERVICES.put("com.sun.jersey.spi.HeaderDelegateProvider",
                com_sun_jersey_spi_HeaderDelegateProvider);
        SERVICES.put("com.sun.jersey.spi.inject.InjectableProvider",
                com_sun_jersey_spi_inject_InjectableProvider);
        SERVICES.put("javax.ws.rs.ext.MessageBodyReader",
                javax_ws_rs_ext_MessageBodyReader);
        SERVICES.put("javax.ws.rs.ext.MessageBodyWriter",
                javax_ws_rs_ext_MessageBodyWriter);
        SERVICES.put("jersey-client-components", new String[]{});
        SERVICES.put("com.sun.jersey.client.proxy.ViewProxyProvider", new String[]{});
    }

    @SuppressWarnings("unchecked")
    @Override
    public Iterator> createClassIterator(Class service,
            String serviceName, ClassLoader loader,
            boolean ignoreOnClassNotFound) {

        String[] classesNames = SERVICES.get(serviceName);
        int length = classesNames.length;
        ArrayList> classes = new ArrayList>(length);
        for (int i = 0; i < length; i++) {
            try {
                classes.add((Class) Class.forName(classesNames[i]));
            } catch (ClassNotFoundException e) {
                Log.v(TAG, MESSAGE,e);
            }
        }
        return classes.iterator();
    }

    @Override
    public Iterator createIterator(Class service, String serviceName,
            ClassLoader loader, boolean ignoreOnClassNotFound) {

        String[] classesNames = SERVICES.get(serviceName);
        int length = classesNames.length;
        ArrayList classes = new ArrayList(length);
            for (int i = 0; i < length; i++) {
            try {
                classes.add(service.cast(Class.forName(classesNames[i])
                        .newInstance()));
            } catch (IllegalAccessException e) {
                Log.v(TAG, MESSAGE,e);
            } catch (InstantiationException e) {
                Log.v(TAG, MESSAGE,e);
            } catch (ClassNotFoundException e) {
                Log.v(TAG, MESSAGE,e);
            }
        }

        return classes.iterator();
    }
}

I removed most of the classes since I didn't use them and also they were causing verification errors on dalvik vm...

NOTE: It means that with this implementation you can use only subset of headers/types supported by Jersey (I needed only String). To support other types you have to add providers located in META-INF/services folder of jersey-client.jar (or from Lucas' implementation) and check if they don't cause verification errors on Android.

The above code should be used as follows:

ServiceFinder.setIteratorProvider(new AndroidServiceIteratorProvider());
Client client = Client.create();

EDIT:

It seems that the problem have been fixed in android-maven-plugin.

mosa...@gmail.com wrote:

The pull request with the fix was merged into master and will be released with 3.2.1: