This document introduces Retrofit, an Android library for making REST API calls. It discusses how to define API interfaces, generate implementations, and make requests. Key features covered include defining endpoints as methods, using interfaces as API specifications, asynchronous requests with callbacks, support for different data format converters, and setting static and dynamic header values. The conclusion states that Retrofit provides a way to avoid issues with incorrect or outdated API documentation.

1. Introduction to Retrofit
or how to say goodbye to
almost correct API doc
第十一回 #渋谷java
Kazuhiro Serizawa

2. About me
• Name: Kazuhiro Serizawa
• Job: Web engineer
• Like: RoR, AngularJS
• Github: serihiro
• Twitter: seri_k
• Blog: http://serihiro.hatenablog.com/

3. What is Retrofit?
• A type-safe REST client for Android and Java
• Created by Square, Inc.
• 5493 Starred (at 2015.5.25)
• Latest version is 1.9.0 (at 2015.5.25)
• Gtihub: https://github.com/square/retrofit
• Docs: http://square.github.io/retrofit/

4. How to use?
In the case you access to Todo API
GET /todo … response todo list with json
GET /todo/:id … response todo with json
POST /todo … create new todo resource
code sample
https://github.com/serihiro/retrofit-implement-samle

5. 1. Define API Interface
public interface TodoService {
@GET("/todos")
List<Todo> list();
@GET("/todos/{id}")
Todo show(@Path("id") Integer id);
@POST("/todos")
void create(@Body Todo todo);
}

6. 2. Implement model class
for API response
public class Todo {
public Integer id = null;
public String todo = "";
public boolean done = false;
public Todo(String todo, boolean done) {
this.todo = todo;
this.done = done;
}
}

7. 3. Generate implementation
for API interface
RestAdapter restAdapter = new
RestAdapter.Builder()
.setEndpoint( http://localhost:3000")
.build();
TodoService todoService =
restAdapter.create(TodoService.class);

8. 4.call api
List<Todo> todos = todoService.list();
Todo todo = todoService.show(1);
todoService.create(new Todo( drink beer , false));

9. Typesafe
• Define endpoints as method
• So rest client with Retrofit knows what
endpoints API has

10. Interface as API
Specification
• Client user can know what endpoint exists
• User get 404 with wrong endpoint name spell !!!
• No more almost correct API documents : )
public interface TodoService {
@GET("/todos")
List<Todo> list();
@GET("/todos/{id}")
Todo show(@Path("id") int id);
@POST("/todos")
void create(@Body Todo todo, Callback<Result> cb);
}

11. feature: ASYNC request
with callback
• Synchronous
• void create(@Body Todo todo)
• Asynchronous
• void create(@Body Todo todo,
Callback<Result> cb);

12. converters
Retrofit uses Gson to parse response body as a
default.
There are following converter class instead of Gson;
• Simple XML Parser(Uses simple framework)
• Jackson
• Google Protocol Buffer
• Wire
source: https://github.com/square/retrofit/tree/master/retrofit-converters

13. feature: static/dynamic
header value
Static Header
@Headers({
"Accept: application/vnd.github.v3.full+json ,
"User-Agent: Retrofit-Sample-App"
})
@GET("/todos")
List<Todo> list();

14. feature: static/dynamic
header value
Dynamic Header
@GET("/todos")
List<Todo> list(@Header("Authorization")
String authorization);

15. Conclusion
Retrofit provides
no more
almost correct
api-document life :)