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 MyClient extends AsyncTask<EditText, Integer, String> {

private EditText text;

protected String doInBackground(EditText... strings) {

    RuntimeDelegate
            .setInstance(new com.sun.ws.rs.ext.RuntimeDelegateImpl());
    WebResource wbr;
    Client client = Client.create();
    wbr = client
            .resource("http://my.ip:8080/MazeService/rest/service/hello");
    String result = wbr.queryParam("number", "10")
            .accept(MediaType.APPLICATION_JSON).get(String.class);
    text = strings[0];
    return result;
}

protected void onProgressUpdate(Integer... progress) {
    // setProgressPercent(progress[0]);
}

protected void onPostExecute(String result) {
    if (result != null)
        this.text.setText(result);
    else
        Log.d("MyApp", "No Result");
}

}

and the Service:

@Path("/service")
public class AndroidService {

@GET
@Produces(MediaType.APPLICATION_JSON )
@Path("/hello")
public String getJSON(@QueryParam("number") String nr)
{

    String s = "Hi there! The number is: "+nr;
    return s;
}
}

I get this stacktrace in LogCat:

02-18 16:26:06.446: E/AndroidRuntime(1381): FATAL EXCEPTION: AsyncTask #1
02-18 16:26:06.446: E/AndroidRuntime(1381): java.lang.RuntimeException: An error occured while executing doInBackground()
02-18 16:26:06.446: E/AndroidRuntime(1381):     at android.os.AsyncTask$3.done(AsyncTask.java:278)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.lang.Thread.run(Thread.java:856)
02-18 16:26:06.446: E/AndroidRuntime(1381): Caused by: java.lang.NullPointerException
02-18 16:26:06.446: E/AndroidRuntime(1381):     at javax.ws.rs.core.MediaType.valueOf(MediaType.java:119)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.ClientResponse.getType(ClientResponse.java:615)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.ClientResponse.getEntity(ClientResponse.java:532)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.ClientResponse.getEntity(ClientResponse.java:506)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.WebResource.handle(WebResource.java:674)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.sun.jersey.api.client.WebResource$Builder.get(WebResource.java:503)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.maze.client.MyClient.doInBackground(MyClient.java:25)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at com.maze.client.MyClient.doInBackground(MyClient.java:1)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at android.os.AsyncTask$2.call(AsyncTask.java:264)
02-18 16:26:06.446: E/AndroidRuntime(1381):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
02-18 16:26:06.446: E/AndroidRuntime(1381):     ... 5 more

I do not understand what the problem is, since a similar client works on PC. There is no problem with the IP address, since I can access the server from the Android VirtualDevice.

The Android version is 4.0.3 API version 15. For the client I used Jersey 1.11.

EDIT

I have also tried to remove the whole thing with the EditText, since someone told me it isn't used as it should be. Still, I got the same error. I simply can not understand what am I doing wrong. If I should display any other additional information, please let me know. Also, ANY idea is good. I am new to Android and I might have made some stupid mistakes.

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<T> extends ServiceIteratorProvider<T> {

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

    private static final HashMap<String, String[]> SERVICES = new HashMap<String, String[]>();

    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<Class<T>> createClassIterator(Class<T> service,
            String serviceName, ClassLoader loader,
            boolean ignoreOnClassNotFound) {

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

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

        String[] classesNames = SERVICES.get(serviceName);
        int length = classesNames.length;
        ArrayList<T> classes = new ArrayList<T>(length);
            for (int i = 0; i &lt; 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.

[email protected] wrote:

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

Answer 2

Following the code:

com/sun/jersey/api/client/ClientResponse.getType()

613    public MediaType getType() {
614        String ct = getHeaders().getFirst("Content-Type");
615        return (ct != null) ? MediaType.valueOf(ct) : null;
616    }

I'd check that the delegate used by MediaType is not null.

javax/ws/rs/core/MediaType.valueOf(java.lang.String)

118    public static MediaType valueOf(String type) throws IllegalArgumentException {
119        return delegate.fromString(type);
120    }

It looks like maybe delegate is null for one client (Android) and not null for your other client.

Take a look at this to get an idea for how the delegate is initialised. It may help your investigations.

javax/ws/rs/ext/RuntimeDelegate.java