Google App Engine and Android playing nice.

I'm a big fan of cloud services, especially when they give you a free or basic quota such as Google App Engine which you can use for development or testing. I’ve done quite a bit of work with Google App Engine before but not in a while. It became a real heavy beast involving importing add ons to Eclipse and configuring a multitude of environment settings.

However recently I've moved to Android Studio and apparently Google Cloud support is built in. Learning this I was then inspired by a recent post on the Android Developers Blog:
http://android-developers.blogspot.co.uk/2014/12/build-mobile-app-services-with-google.html

I felt this wasn't a great tutorial, there were large sections left out and it basically didn't work nearly as easily as I’d hoped it would. Sorry Android Developers, but not your best work. Still the steps to get started were simple enough:

1. Create a super simple Android app. Basic Hello world stuff.
2. Give your app Internet permissions
3. Create a new Google Cloud Module
   • File -> New Module
   • Click “Google Cloud Module”
   • Select App Engine Java Endpoints Module

Android studio will now create a GAE backend module for you and automatically tie it into your Android app. Now you need a bean and an endpoint.

MyBean.java

package com.example.myapplication.backend;

public class MyBean {

    private String myData;

    public String getData() {
        return myData;
    }

    public void setData(String data) {
        myData = data;
    }
}

MyEndpoint.java

package com.example.myapplication.backend;

import com.google.api.server.spi.config.Api;
import com.google.api.server.spi.config.ApiMethod;
import com.google.api.server.spi.config.ApiNamespace;

import javax.inject.Named;

/**
 * An endpoint class we are exposing
 */
@Api(name = "myApi", version = "v1", namespace = @ApiNamespace(ownerDomain = "backend.myapplication.example.com", ownerName = "backend.myapplication.example.com", packagePath = ""))
public class MyEndpoint {

    /**
     * A simple endpoint method that takes a name and says Hi back
     */
    @ApiMethod(name = "sayHi")
    public MyBean sayHi(@Named("name") String name) {
        MyBean response = new MyBean();
        response.setData("Hi, " + name);

        return response;
    }

}

and here’s the Gradle file:

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.google.appengine:gradle-appengine-plugin:1.9.14'
    }
}

repositories {
    mavenCentral();
}

apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'appengine'

sourceCompatibility = JavaVersion.VERSION_1_7
targetCompatibility = JavaVersion.VERSION_1_7

dependencies {
    appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.14'
    compile 'com.google.appengine:appengine-endpoints:1.9.14'
    compile 'com.google.appengine:appengine-endpoints-deps:1.9.14'
    compile 'javax.servlet:servlet-api:2.5'
}

appengine {
    downloadSdk = true
    appcfg {
        oauth2 = true
    }
    endpoints {
        getClientLibsOnBuild = true
        getDiscoveryDocsOnBuild = true
    }
}

Frustratingly you’ll get red errors all over the place. Cannot resolve symbol api. This really winds me up and I’ve not yet figured out how to fix it. However it does build and run with these problems, so not really an error!

If you change the run drop down to “backend” and hit run hopefully this will all compile and you’ll get an Android Studio message with a localhost url. This is Android Studio setting up a local version of Google App Engine and using Jetty to host it. You should see a url output which you can copy to your browser, something like:
http://localhost:8080/

Hitting this url you should get an index file saying Hello Endpoints or something with a nice pretty bootstrap wrapper. You can enter something into the text field and your GAE application will say Hi to you.

Now we need to plug this into our Android app. First we need a new AsyncTask

package tester.example.com.myapplication;

import android.content.Context;
import android.os.AsyncTask;
import android.support.v4.util.Pair;
import android.widget.Toast;

import com.example.myapplication.backend.myApi.MyApi;

import com.google.api.client.extensions.android.http.AndroidHttp;
import com.google.api.client.extensions.android.json.AndroidJsonFactory;
import com.google.api.client.googleapis.services.AbstractGoogleClientRequest;
import com.google.api.client.googleapis.services.GoogleClientRequestInitializer;


import java.io.IOException;

class EndpointsAsyncTask extends AsyncTask<Pair<Context, String>, Void, String> {
    private static MyApi myApiService = null;
    private Context context;

    @Override
    protected String doInBackground(Pair<Context, String>... params) {
        if(myApiService == null) {  // Only do this once
            MyApi.Builder builder = new MyApi.Builder(AndroidHttp.newCompatibleTransport(),
                    new AndroidJsonFactory(), null)
                    // options for running against local devappserver
                    // - 10.0.2.2 is localhost's IP address in Android emulator
                    // - turn off compression when running against local devappserver
                    .setRootUrl("http://10.0.2.2:8080/_ah/api/")
                    .setGoogleClientRequestInitializer(new GoogleClientRequestInitializer() {
                        @Override
                        public void initialize(AbstractGoogleClientRequest<?> abstractGoogleClientRequest) throws IOException {
                            abstractGoogleClientRequest.setDisableGZipContent(true);
                        }
                    });
            // end options for devappserver

            myApiService = builder.build();
        }

        context = params[0].first;
        String name = params[0].second;

        try {
            return myApiService.sayHi(name).execute().getData();
        } catch (IOException e) {
            return e.getMessage();
        }
    }

    @Override
    protected void onPostExecute(String result) {
        Toast.makeText(context, result, Toast.LENGTH_LONG).show();
    }
}

Now in your app activityMain or somewhere, fire a call to the AsyncTask:

new EndpointsAsyncTask().execute(new Pair(this, "Manfred"));

The dependencies in your Android app should look like this:

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:21.0.3'
    compile 'com.google.android.gms:play-services:6.1.71'
    compile project(path: ':backend', configuration: 'android-endpoints')
}

Now if you run your Android app in a Android Virtual Device, you should see your local server respond with a Hi Message.

This is a pretty basic example, but you get the idea and its a great first step on the path toward Android and Google Cloud playing well together.