Build an efficient REST Client on Android - Droidcon IT 2016 - Matteo Gazzurelli

Build an eﬃcient REST Client on Android

© DuckMa 2016 - www.duckma.com
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Have you ever parsed a JSON string by hand?
Do you still use plain HttpUrlConnection to
connect to a server?
Do you have an app that consumes a REST endpoint?

A Good 
REST Client
THE MAIN INGREDIENTS OF A FAST WEB API
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CachingHttp 2

HTTP 2
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• Based on Google’s SPDY
• Supported by most browsers
• goals: reducing web page load latency
and improving web security
https://http2.github.io/faq

CACHING
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• Caching System (Good for Dynamic APIs)
• APC
• Varnish
• Memcache

CACHING
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• HTTP Headers (Good for Static APIs)
• Expires
• Cache-Control
• Entity Tags
• Last-Modiﬁed

WHAT IS REST?
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• Representational State Transfer (REST)
• REST is an architectural style consisting of a
coordinated set of architectural constraints
applied to components, connectors, and data
elements
• REST is platform and language independent.

REST KEY PRINCIPLE
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• Give every “thing” an ID
• Link things together
• Use standard methods
• Resources with multiple representations
• Communicate statelessly
http://www.infoq.com/articles/rest-introduction

REST (HTTP) CLIENTS IN ANDROID
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• DefaultHttpClient / HttpUrlConnection
• Volley
• Spring
• Retroﬁt
• …

WHAT IS RETROFIT
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Type-safe HTTP client for Android and Java by
Square, Inc.
Uses annotations to describe HTTP requests
and URL parameter replacement
Retroﬁt turns your REST API into a Java
interface.

RETROFIT CONVERTERS
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Converters can be added to support other types.
• Gson
• Jackson
• Moshi
• Protobuﬀer
• Wire
• Simple XML
• Scalars (primitives, boxed, and String)

RETROFIT 101
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•Create a POJO/JavaBean Model
•Create Retroﬁt Interface
•Create the Call object
•Execute the request
•Use the result

RETROFIT MODEL EXAMPLE
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public class Content {
String id;
String title;
String image;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}

RETROFIT INTERFACE EXAMPLE
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public interface AppAPI {
@GET("/")
@Headers({"Cache-Control: public, only-if-cached, max-
stale=2147483647"})
Call<ContentResponse> loadCachedContents();
}

RETROFIT CALL EXAMPLE
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mAppApi = retroﬁt.create(AppAPI.class);
Call<ContentResponse> call = mAppApi.loadContents();
call.enqueue(this);
@Override
public void onResponse(Call<ContentResponse> call,
Response<ContentResponse> response) {}
@Override
public void onFailure(Call<ContentResponse> call, Throwable
t) {}

RETROFIT (A)SYNC CALLS
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If you want to execute a synchronous call just replace
call.enqueue() with call.execute()
remember that you have to perform this outside the main
thread
To cancel a running request
call.cancel();
calls can only be used once but you can easily clone them
Call<ContentResponse> c = call.clone();
c.enqueue(this);

WHAT’S NEW IN RETROFIT 2
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• Package with New Version (avoid conﬂicts)
• New Service Declaration
• A way to cancel the ongoing transaction
• New Url resolving concept
• OkHttp is now required

WHAT IS OKHTTP
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OkHttp is an HTTP client that’s eﬃcient by default:
• HTTP/2 support allows all requests to the same host to share
a socket.
• Connection pooling reduces request latency (if HTTP/2 isn’t
available).
• Transparent GZIP shrinks download sizes.
• Response caching avoids the network completely for repeat
requests

OKHTTP - NOT ONLY FOR RETROFIT
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Can be used as http client for other libraries:
• Picasso
• Glide
• Fresco
Okio Dependent: Okio is a new library that
complements java.io and java.nio to make it much
easier to access, store, and process your data.

INTERCEPTORS
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Powerful mechanism that can monitor,
rewrite, and retry calls.
Interceptors can be chained and are
called in order.
https://github.com/square/okhttp/wiki/Interceptors

RETROFIT AND OKHTTP INTERCEPTOR
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OkHttpClient client = new OkHttpClient();
client.interceptors().add(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Response response = chain.proceed(chain.request());
return response;
}
});
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(“http://test-project-json.appspot.com”)
.addConverterFactory(GsonConverterFactory.create())
.client(client)
.build();

LOGGING
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Latest version of OkHttp ships with a logging interceptor
compile 'com.squareup.okhttp3:logging-interceptor:3.2.0'
HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient client = new OkHttpClient.Builder()
.addInterceptor(interceptor).build();

TWO LEVEL OF CACHING
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• Soft Caching (Network level)
• Persistent Caching (Database)

SOFT CACHING WITH OKHTTP
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•OkHttp as caching bucket
•Response caching uses HTTP headers for all
conﬁguration.
•There are cache headers to force a cached
response, force a network response, or force
the network response to be validated with a
conditional GET.

SOFT CACHING WITH OKHTTP
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OkHttpClient.Builder okBuilder = new
OkHttpClient.Builder();
Cache cache = new Cache(new File(getCacheDir(),
CACHE_DIR), CACHE_SIZE);
okBuilder.cache(cache);
Private cache directory

PERSISTENT CACHING
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Various Android Storage Options:
•Shared Preferences
•Internal/External Storage
•Sqlite
•Realm.io

REALM.IO
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Realm is a replacement for SQLite
• Uses little resources
• Easy to use
• Fast
• Cross-Platform (C++)
• Advanced
https://realm.io/docs/java/latest/#getting-started

REALM IS FAST
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Tests run on an Galaxy S3, using the latest available version of each library as of Sept 28, 2014.

REALM LIST / PROXY CLASSES
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The RealmProxy classes are our way of making
sure that the Realm object doesn’t contain any
data itself, but instead access the data directly in
the database.

REALM WITH RETROFIT
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https://realm.io/docs/java/latest/#retroﬁt
Retroﬁt does not automatically add objects
to Realm, instead you must manually add
them using the realm.copyToRealm() or
realm.copyToRealmOrUpdate() methods.

REALM WITH RETROFIT
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@Override
Response<ContentResponse> response) {
if (response.isSuccessful()) {
mRealm.beginTransaction();
mRealm.copyToRealm(mContentsArray);
mRealm.commitTransaction();
}
}

BACKEND? APPENGINE
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Easy and fast way to create http2 backend
https://console.developers.google.com.

APPENGINE - FLASK (PYTHON)
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@app.route('/')
def returnJson():
folder = 'json/app.json'
f = open(folder,'r')
resp = Response(response=f.read(),
status=200,
mimetype="application/json")
return resp
Create a static json ﬁle to be served

BACKEND?
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http://blog.duckma.com/2016/01/how-to-create-
simple-project-in-google.html
If you want to start using Google App Engine,
Start Here: https://console.cloud.google.com/start/appengine

DEMO
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https://github.com/duckma/Rest-Client-Demo
• Retroﬁt
• Gson
• Interceptor
• OkHTTP
• Caching
• realm.io

DEMO
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Download app: duk.ma/droidconit2016

DEMO SOFT CACHE
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• D/OkHttp: --> GET http://test-project-json.appspot.com/
• D/OkHttp: --> END GET
• D/OkHttp: <-- 200 OK http://test-project-json.appspot.com/ (322ms)
• D/OkHttp: <-- END HTTP
• D/OkHttp: --> GET http://test-project-json.appspot.com/
• D/OkHttp: Cache-Control: public, only-if-cached, max-stale=2147483647
• D/OkHttp: --> END GET
• D/OkHttp: <-- 200 OK http://test-project-json.appspot.com/ (6ms)
• D/OkHttp: Warning: 110 HttpURLConnection "Response is stale"
• D/OkHttp: <-- END HTTP

RETROFIT INTERFACE EXAMPLE
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public interface AppAPI {
String FORCE_CACHE_HEADERS =
"Cache-Control: public, only-if-cached, max-stale=" +
Integer.MAX_VALUE;
@GET("/")
Call<ContentResponse> loadContents();
@GET("/")
@Headers({FORCE_CACHE_HEADERS})
Call<ContentResponse> loadCachedContents();
}

DEMO PERSISTENT CACHE
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@Override
public void onFailure(Call<ContentResponse> call,
Throwable t) {
RealmResults<Content> results =
mRealm.where(Content.class).ﬁndAll();
mContentsArray.addAll(results);
mAdapter.notifyDataSetChanged();

SAVE DATA IN REALM
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@Override
Response<ContentResponse> response) {
mContentsArray.clear();
if (response.isSuccessful()) {
mContentsArray.addAll(response.body().getContents());
mRealm.beginTransaction();
mRealm.copyToRealm(mContentsArray);
mRealm.commitTransaction();

CONTENT MODEL
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public class Content extends RealmObject {
String id;
String title;
String image;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}

GSON CONVERTER
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Gson gson = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
@Override
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
}
@Override
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
})
.create();
https://code.google.com/p/google-gson/issues/detail?id=440

RETROFIT CLIENT WITH OKHTTP
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OkHttpClient.Builder okBuilder = new OkHttpClient.Builder();
Cache cache = new Cache(new File(getCacheDir(), CACHE_DIR),
CACHE_SIZE);
okBuilder.cache(cache);
HttpLoggingInterceptor logInterceptor = new HttpLoggingInterceptor();
logInterceptor.setLevel(HttpLoggingInterceptor.Level.HEADERS);
okBuilder.addInterceptor(logInterceptor);
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(Config.ENDPOINT)
.addConverterFactory(GsonConverterFactory.create(gson))
.client(okBuilder.build())
.build();

WHO AM I ?
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Matteo Gazzurelli
CEO
DuckMa
DuckMa is a mobile focused design and software boutique primarily working with startups and leading brands.
We are a group of passionate professionals who make handcrafted mobile native apps.
San FranciscoBrescia

THANK YOU
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We are hiring!
duk.ma/jobpositions

Build an efficient REST Client on Android - Droidcon IT 2016 - Matteo Gazzurelli

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