Presented at CASE27 Conference in Zagreb, Croatia. Abstract: Most of today’s mobile applications use one or more communication technologies to send and retrieve data stored online. In majority of these cases applications actually communicate with back-end web service which sends and receives the data. Today’s most popular architecture that deals with this functionality, is called REST (Representation State Transfer) architecture, but, implementing REST client in native Android applications usually takes a lot of time, and if it is not implemented by using some architectural pattern, time needed to modify the implementation grows proportionally with application complexity. Industry recognized one helpful framework, Retrofit, which aims to speed up the process and leaves developers more time to focus on the other important activities in the system development process. To reduce even more boilerplate code, Retrofit uses Java annotations which speed up the development process even more. Thus, in this paper we present Retrofit framework and we compare it with native implementation of Android REST client.

1. Using Retrofit framework in implementation of
Android REST client
David Ante Macan*, Zlatko Stapić, Milan Pavlović*
University of Zagreb
Faculty of Organization and Informatics
Pavlinska 2, 42000 Varaždin, Croatia
http://www.foi.unizg.hr/
CASE27 – Developers conference - 02.06.2015. – Zagreb, Croatia
* Students at University of Zagreb, FOI Varazdin

2. Agenda
• Introduction
• REST Architecture
• Android client implementation
• Implementation using Retrofit
• Conclusion
• References
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20152

3. Introduction
• Today’s mobile applications are Internet dependent
• 2017 -> 90% [1], [3]
• Web services are used for supporting mobile application
functionalities
 Internet dependent monetization models
 App usage statistics, data synchronization, social components, score
tables…
• Backend servers for push notifications
• Web service – self contained and self describing application
component that can be used by other applications and can be
communicated by using open protocols [6]
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20153

4. Introduction
• After SOA became widely used for mobile and other applications,
the dominant way of exchanging the data with web services was
by using SOAP [7]
• XML used for creating requests and responses was too complex
and requests had to be build manually -> problematic due to
protocols intolerance on any errors
• REST (Representational State Transfer) provides lightweight
alternative and relies on simple URL approach
• REST can output the data in any format (for example in CSV, JSON
or RSS).
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20154

5. REST Architecture
 Architectural style for distributed hypermedia systems, as Roy
Fielding originally described it in his doctoral dissertation in 2000
[8]
 Contains 6 main characteristics:
1. Uniform interface
 Resource based
 Manipulation of resources through representations
 Usage of self-descriptive messages
 Hypermedia as the engine of application state
2. Statelessness
3. Caching
4. Client-server separation
5. Layering
6. Code on demand
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20155

6. REST Architecture
 HTTP request semantics
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20156
Request Method Description
GET
Used for retrieving (or read) a representation of a
resource. If everything works, HTTP GET response
contains a representation in XML or JSON with
response code of 200 (OK).
POST
Most often used for creation of new resources. It is
actually used to create subordinate or child resource of
some other (parent) resource. When server receives
POST request, it creates new resource and assigns it a
new ID.
PUT
Used for update operations. Request body should
contain newly-updated representation of the original
resource which is identified by a known resource URI.
DELETE Used to delete URI-identified resource.

7. Android client implementation
• Example system
 Address Manager - enables users to get geographical location (latitude
and longitude) of any user defined address
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20157

8. Android client implementation
• Web service specification
 http://tinyurl.com/case27-locations
 x-www-form-urlencoded request
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20158
URL Method Params Response example
base GET - [{"id":1,"location":"Ivanec","lat":
"46.2228422","lon":"16.1246793"},
…]
base POST location {"id":1,"location":"Ivanec","lat":
"46.2228422","lon":"16.1246793"}
base/id PUT location {"id":1,"location":"Ivanec 2", "lat":
"47.2228422","lon":"15.1246793"}

9. Android client implementation
• Native Android web-service consumption
 web service communication layer
 response parsing layer
 manual threading
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 20159

10. Android client implementation
• Native Android web-service consumption
 Repository – consists of set of methods that are leaning on web
services
 Service – represents web-service communication layer. This class
should be flexible to be able to execute any web service request.
 Callback – interface to be implemented by any callback object
containing logic for receiving web-service response.
 Parser – static class containing knowledge on parsing the responses.
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201510

11. Android client implementation
• Native
Repository
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201511

12. Android client implementation
• Retrofit implementation
 type-safe REST client for Android and Java
 turns your REST API into a Java interface
 upon downloading the data
is parsed into POJO which
must be defined for each
"resource" in the response
 flexible in message format
 uses compile-time annotation
processor
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201512

13. Android client implementation
• Retrofit implementation
 Define API interface
 Define RetrofitHelper that will instantiate adapter and interface
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201513

14. Android client implementation
• Retrofit implementation
 Call methods
 Handle response
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201514

15. Conclusion
• We presented
 REST application architectural style
 Two implementations of web-service communication layer
• Main contribution
 Architectural design for the two approaches
• Native vs Retrofit approach
 Native approach is robust and hard to adapt
 Retrofit is straightforward and flexible
• Source code
 http://tinyurl.com/case27-code
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201515

16. References
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http://www.smartinsights.com/mobile-marketing/mobile-marketing-analytics/mobile-marketingstatistics/ [Accessed: May-2015]
[2] ComScore Inc., “The U.S. Mobile App Report” 2014. Available at:
http://www.comscore.com/Insights/Presentations-and-Whitepapers/2014/The-US-Mobile-App-Report
[3] Statista, “Statistics and facts on Mobile Internet Usage,” Statista.com, 2015. [Online]. Available at:
http://www.statista.com/topics/779/mobile-internet/ [Accessed: May-2015].
[4] Android Developers, “Google Cloud Messaging for Android | Android Developers” Google Services,
2015. [Online]. Available at: https://developer.android.com/google/gcm/index.html [Accessed: May-2015].
[5] Apple inc., “Local and Push Notifications for Developers - Apple Developer” Developer Apple.com,
2015. [Online]. Available at: https://developer.apple.com/notifications/ [Accessed: May-2015].
[6] W3Schools.com, “Introduction to Web Services” Introduction to Web Services, 2015. [Online]. Available
at: http://www.w3schools.com/webservices/ws_intro.asp [Accessed: May-2015].
[7] W3Schools.com, “SOAP Introduction”, 2015. [Online]. Available at: http://www.w3schools.com/
webservices/ws_soap_intro.asp [Accessed: May-2015].
[8] R. T. Fielding, “Architectural Styles and the Design of Network-based Software Architectures”
UNIVERSITY OF CALIFORNIA, Irvine, 2000.
[9] A. Nene, “Web Services Architecture – When to Use SOAP vs REST” Javalobby, 2014. [Online]. Available
at: http://java.dzone.com/articles/web-services-architecture [Accessed: May-2015].
[10] J. Mueller, “Understanding SOAP and REST Basics” Software Quality Matters Blog, 2013. [Online].
Available at: http://blog.smartbear.com/apis/understanding-soap-and-rest-basics/ [Accessed: May-2015].
[11] F. Todd, “RESTful Service Best Practices, Recommendations for Creating Web Services”
RestAPITutorial.com, 2013.
[12] CodePath.com, “Consuming APIs with Retrofit” CodePath Android Cliffnotes, 2015. [Online]. Available
at: https://guides.codepath.com/android/Consuming-APIs-with-Retrofit#setup [Accessed: May-2015].
[13] StudyTrials, “Java Google Json (Gson) Introduction” StudyTrials.com. [Online]. Available at:
http://www.studytrails.com/java/json/java-google-json-introduction.jsp [Accessed: May-2015].
[14] “Google Gson” Google Gson Home, 2011. [Online]. Available at: https://sites.google.com/
site/gson/Home [Accessed: May-2015]
Macan, Stapić, Pavlović: Using Retrofit framework in implementation of Android REST client - CASE27, 2nd June 201516