Retrofit: Love Working with APIs on Android
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Retrofit: Love Working with APIs on Android

Take delight in building API clients on Android.

About the Book

Painless Networking with Retrofit

The content of this book is completely updated to Retrofit 2.5!

Every modern Android app needs to connect to at least one private or public API. Interacting with services can be difficult due to the extreme variety of request and response formats. Depending on the API, you’ll need to change your request payloads, authentication, data formats, and much more.

Retrofit: a type-safe HTTP client for Android and Java

Retrofit handles all of the complicated and repetitive parts of network implementations for you. It hides the entire network layer, from creating a connection to processing the handling on a separate thread, from you. Retrofit even does the mapping of the requests and responses to Java objects for you (e.g., creating a JSON payload from your passed List<User>). You only need to describe what and how you want to send or receive it.

This awesomeness comes at a cost: an initial learning curve. Retrofit might look a little more complicated at the beginning, but pays off multiple times in the long run.

If you’re thinking about using Retrofit, or haven’t developed a deep knowledge of it yet, you’ll benefit from this book. We’ve created this book with the vision of being the ultimate guide to understanding Retrofit. After working through this book, you’ll be able to connect to new APIs and services within minutes.

You can find a Retrofit tutorial series on our website and our free video tutorial series on YouTube, where we describe some elements of Retrofit. The book extends and connects these tutorials into one common thread that guides you through all important aspects of Retrofit. The chapters are structured in a way that rewards a linear reading. Retrofit rookies can and should read it cover to cover. Experienced Retrofit developers can jump to specific sections for guides on how to solve their specific problem.

What Topics Are Covered in This Book?

The list below provides a comprehensive overview of covered topics in the book.

  • Introduction to Retrofit
  • Quick Start Guide to jump right into Retrofit
  • Creating a sustainable Android REST client
  • Extensive manipulation and customization of requests (e.g., query and path parameters, form-urlencoding, synchronous vs. asynchronous)
  • Cancel, analyze and re-use requests
  • Comprehensive overview of response converters and data mapping with plenty practical examples of applied (custom) converters
  • Implementing and handling authentication (basic, token, OAuth, hawk) in a smart way
  • File uploads, including multiple and dynamic amounts of files (optionally with progress updates)
  • File download (optionally with progress updates)
  • Detailed chapter on implementing pagination
  • Introduction and example of possible ways to deal with errors in a clean way
  • Debug requests and responses using three logging tools (OkHttp, Stetho, Android Studio Profiler)
  • Fundamentals for mocking server responses
  • Entire chapter on practical examples of custom converters dealing with specific scenarios
  • Detailed introduction to call adapters, including custom implementations
  • Extensive chapter on implementing response caching with Retrofit
  • Example for an offline mode based on cached server responses
  • A chapter with practical tips & tricks (including crawling websites with Retrofit)
  • App release preparation including ProGuard configuration

Additionally to the regular content we provide an appendix with three sections:

  • Upgrade guide from Retrofit 1.9 to 2.0
  • Java basics for Retrofit
  • Network basics for developers, who just started interacting with APIs

Who Is This Book For?

In short: this book is for you. We believe that every developer reading this book will take away new ideas on how to optimize their Android apps in the sense of interacting with APIs or web services using Retrofit. You’ll recognize goodies that are applicable for the projects you’re working on.

This book is for Android developers, who want to receive a substantial overview and reference book on Retrofit. You’ll benefit from clearly recognizable code examples related to your daily work with Retrofit.


If you’re just starting out with Retrofit (or coming from another HTTP library like Android Asynchronous Http Client or Volley) this book will show you all important parts on how to create sustainable REST clients on Android. The provided code snippets let you jumpstart and create your first successful API client within minutes!


If you’ve already worked with Retrofit, you’ll profit from our extensive code snippets and apply the learnings to your existing code base. Additionally, the book illustrates various use cases for different functionalities and setups like authentication against different backends, request composition, file uploads and downloads, and much more!

One focus of this book is not only to implement the requirements, but also do so in a clean way. We’ve seen way to many complicated and messy usages of Retrofit. We focus on providing code samples which adhere to clean code standards. We avoid any unnecessary duplication at all costs. This has the side effect of some extra app performance gains by efficient Java object handling.

Source Code Samples

With the purchase of this book, you benefit from the sample project that awaits your download within the extras section on Leanpub. The sample project is an Android project based on gradle. You can directly touch and use classes that are only illustrated in excerpts within this book.

Check your Leanpub Library and select Retrofit: Love working with APIs on Android to download the sample code base.

Continuous Updates

We’ve published the first version of this Retrofit book in July 2015. Since this initial release we’ve extended and updated the book more than a dozen times. Once you buy the book, you get all future updates for free. Even if it’s a huge Retrofit update, for example from version 1.9 to 2.0. With every new release of Retrofit we’ll evaluate the entire book content and update it accordingly.

Of course, we’re listening to your feedback and add new sections and even chapters, if it can be useful to all readers. If you still have a question after reading this book, let us know and we might be able to help!

Still Unsure?

If you’re still on the fence if this book helps you, checkout the sample or, even better, use Leanpub’s (and our) happiness guarantee. Try this book out and if you don’t think this book provides enough value, you can refund your money within 45 days with no questions asked. You don’t have any risk in testing this book, which saves you hours of headaches and makes your Android app code so much cleaner.

Final Note: Retrofit Book for Version 1.9

The current version of this book is fully focused on Retrofit 2.x, no hint or code snippet that points to Retrofit 1. If you’re interested in the first version of the book that based on Retrofit 1, please visit this book’s extras page on Leanpub. As a reader of this book, the first version is also available for you!

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About the Author

Future Studio
Marcus Pöhls

Marcus is an enthusiastic Android & Java developer. He’s developed multiple production-ready client and server applications. While following the core principle of performance for client apps, he also builds REST+JSON APIs that focus on clear and consistent design.

Besides his day job, sharing knowledge and teaching others has become a characteristic he never wants to miss.

Marcus has a Master’s degree in computer science from the Otto von Guericke University Magdeburg.

Feel free to get in touch on Twitter @marcuspoehls.

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About the Contributors

Norman Peitek
Norman Peitek

Norman is passionate Android developer since 2011. He's developed multiple apps, which have been used by millions of users overall. Building high-quality products is always Norman's #1 focus. While working as an Android freelancer and consultant is his day job, he loves teaching and passing on knowledge on the side.

Since 2014, Norman started working on the API side as well. Developing node.js apps is a good alternative and provides some good insight into becoming a better programmer overall.

Norman has a Master's degree from the Otto von Guericke University Magdeburg.

Feel free to get in touch on twitter @peitek or LinkedIn.

Table of Contents

  • Introduction
    • What Topics Are Waiting for You?
    • Who Is This Book For?
    • The Source Code
    • Retrofit Book for Version 1.9
  • Chapter 1 — Quick Start & Create a Sustainable REST Client
    • Retrofit Overview
    • Why Use Retrofit?
    • Retrofit vs. OkHttp
    • Quick Start: Add Retrofit to Your Project
    • Sustainable Android REST Client
    • The ServiceGenerator
    • Retrofit in Use
  • Chapter 2 — Requests
    • Retrofit API Declaration
    • Url Handling, Resolution and Parsing
    • Query Parameter
    • Path Parameter
    • Synchronous and Asynchronous Requests
    • Send Objects in Request Body
    • Constant, Default and Logic Values for POST and PUT Requests
    • Send Data Form-Urlencoded
    • Add Request Header
    • Reuse, Analyze & Cancel Requests
    • Customize Network Timeouts
    • Ignore Response Payload with Call<Void>
  • Chapter 3 — Data Mapping with Retrofit Converters
    • Integrate a JSON Converter
    • Integrate an XML Converter
    • Integrate Other Standard Formats
    • Deal with Multiple Converters
    • Integrate Your Own Custom Converter
    • Access Mapped Objects and Raw Response Payload
    • Further Custom Converter Examples
  • Chapter 4 — Authentication
    • Authentication Interceptor
    • Basic Authentication
    • Token Authentication
    • OAuth 2
    • OAuth — Refresh Your Access Token
    • Hawk Authentication
    • Dynamic Endpoint-Dependent Interceptor Actions
  • Chapter 5 — File Upload & Download
    • File Upload
    • Upload of Multiple Files
    • Upload of Dynamic Amount of Files
    • Uploading Files with Progress Updates
    • Passing Multiple Parts Along a File with @PartMap
    • File Download
    • File Download with Progress Updates
  • Chapter 6 — Pagination on Android
    • Pagination Response Status
    • Pagination Using Query Parameter
    • Pagination Using Link Header and Dynamic Urls (Like GitHub)
    • Pagination Using Range Header Fields (Like Heroku)
  • Chapter 7 — Error Handling
    • Error Handling Preparations
    • Simple Error Handler
    • Error Handling for Synchronous Requests
    • How to Detect Network and Conversion Errors in onFailure
    • Catch Server Errors Globally with Response Interceptor
  • Chapter 8 — Logging
    • Log Requests and Responses with Retrofit
    • Enable Logging for Debug Builds Only
    • Log Network Traffic with Stetho and Chrome Developer Tools
    • Analyze Network Traffic with Android Studio Profiler
  • Chapter 9 — Multiple Server Environments
    • Product-Flavor-Dependent Base URLs
    • Change API Base URL at Runtime
  • Chapter 10 — Caching
    • Activate Response Caching (Etag, Last-Modified)
    • Check Response Origin (Network, Cache, or Both)
    • Analyze Cache Files
    • Force Server Cache Support with Response Interceptor
    • Support App Offline Mode by Accessing Response Caches
  • Chapter 11 — Client-Side Mocking of Server Responses
    • Why Mocking Responses Make Sense
    • Create Your Own MockRetrofit Implementation
    • Customizing Network Behavior of Mocked Server Responses
  • Chapter 12 — Practical Converters
    • Handling of Empty Server Responses
    • Supporting JSON and XML Responses Concurrently
    • Send JSON Requests and Receive XML Responses (or vice versa)
    • Unwrapping Envelope Responses
    • Wrapping Requests in Envelope
  • Chapter 13 — Call Adapters
    • Call Adapter Basics — What Are They?
    • Integration of Retrofit Callbacks into Your RxJava 1 Flow
    • Integration of Retrofit Callbacks into Your RxJava 2 Flow
    • Integration of Retrofit Callbacks into Your Guava Flow
    • Separating onResponse Callback with Custom Call Adapter
    • Separating onFailure Callback with Custom Call Adapter
  • Chapter 14 — Practical Usages
    • Share OkHttp Client and Converters between Retrofit Instances
    • How to Trust Unsafe SSL certificates (Self-signed, Expired)
    • Receive Plain-String Responses
    • Crawl HTML Responses with jspoon (Wikipedia Example)
  • Chapter 15 — App Release Preparation
    • Enable ProGuard
    • Configure ProGuard Rules for Retrofit
    • Obfuscated Stack Traces
  • Appendix A — Retrofit 2 Upgrade Guide from 1.x
    • Introduction
    • Maven & Gradle Dependencies
    • RestAdapter —> Retrofit
    • setEndpoint —> baseUrl
    • Base Url Handling
    • Dynamic Urls
    • OkHttp Required
    • Interceptors Powered by OkHttp
    • Synchronous & Asynchronous Requests
    • Cancel Requests
    • No Default Converter
    • RxJava Integration
    • No Logging
    • Future Update: WebSockets in Retrofit 2.2
    • Conclusion
  • Appendix B — Java Basics for Retrofit
    • Java Annotations
    • Java Callbacks
    • Fluent Interface with Builders
  • Appendix C — Network Basics for Retrofit
    • HTTP Basics
    • Client Requests
    • Request Methods
    • Server Responses
    • Status Codes
    • Future Protocols
  • Outro
  • Future Studio Books
    • Gson
    • Glide
    • Picasso
    • Future Studio Bundle

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