Implementing Retrofit in Your Android Application

Transcript

1. Implementing Retrofit In Your Android Application By Pascal How Mobile Software Engineer at MyDrive Solutions
2. What is Retrofit • Type-Safe REST client using annotations to describe HTTP requests • Framework to interact with APIs and sending network requests • Automatically parses downloaded data into a Plain Old Java Object
3. Old Way: Async Tasks • No screen orientation support • No ability to cancel network calls • No easy way to make API calls in parallel
4. AsyncTasks public class HttpGetRequest extends AsyncTask < String, Void, String > { public static final String REQUEST_METHOD = "GET"; public static final int READ_TIMEOUT = 15000; public static final int CONNECTION_TIMEOUT = 15000; @Override protected String doInBackground(String...params) { String stringUrl = params[0]; String result; String inputLine; try { //Create a URL object holding our url URL myUrl = new URL(stringUrl); //Create a connection HttpURLConnection connection = (HttpURLConnection) myUrl.openConnection(); //Set methods and timeouts connection.setRequestMethod(REQUEST_METHOD); connection.setReadTimeout(READ_TIMEOUT); connection.setConnectTimeout(CONNECTION_TIMEOUT); //Connect to our url connection.connect() //Create a new InputStreamReader InputStreamReader streamReader = new InputStreamReader(connection.getInputStream()); //Create a new buffered reader and String Builder BufferedReader reader = new BufferedReader(streamReader); StringBuilder stringBuilder = new StringBuilder(); //Check if the line we are reading is not null while ((inputLine = reader.readLine()) != null) { stringBuilder.append(inputLine); } //Close our InputStream and Buffered reader reader.close(); streamReader.close(); //Set our result equal to our stringBuilder result = stringBuilder.toString(); } catch (IOException e) { e.printStackTrace(); result = null; } return result; } protected void onPostExecute(String result) { super.onPostExecute(result); } } Now imagine making many network calls at the same time!
5. Why Use Retrofit? • Super easy to use! ◦ Only define URLs to hit ◦ JSON Parsing is all done for you • Supports async requests with minimal code ◦ NO MORE ASYNCTASKS + Manual Json parsing • Great Documentation and Community
6. Why Use Retrofit?
7. Retrofit For Dummies! • Add dependencies • Describe API endpoints • JSON Mapping • Prepare Request With OkHttp and Retrofit
8. Setting Up Retrofit Set Retrofit as a dependency in gradle dependencies { compile 'com.squareup.retrofit2:retrofit:2.2.0' compile 'com.squareup.retrofit2:converter-gson:2.2.0' } Android Network Permission <uses-permission android:name="android.permission.INTERNET" /> JSON Converter
9. Leveraging OkHttp OkHttpClient • This is what makes the actual HTTP request within Retrofit • More efficient than standard Java I/O library for reading and writing data • Works best with a single instance across application ◦ Each new instance gets its own private connection pool ◦ Creating many will prevent connection reuse ◦ Each connection pool holds its own set of connections alive ◦ Too many connection pools will exhaust memory
10. Describing API Endpoints public interface GitHubService { @GET("/users/pascalhow/repos") Call <List<Repo>> listRepos(); @POST("/user/info") Call <List<UserInfo>> updateUserInfo(@Body UserInfo userInfo); @DELETE("/user") Call <Void> deleteUser(); }
11. JSON Mapping • Requests to a server and responses from the server not Java objects • Usually JSON format TIPS • Automatically create Java class using jsonschema2pojo
12. JSON Mapping public class UserInfo { @SerializedName("id") private int userId; @SerializedName("name") private String userName; @SerializedName("activities") private Activities activities; // Getters and setters }
13. Making the Request Retrofit REST Client Retrofit retrofit = new Retrofit.Builder() .baseUrl("https://api.github.com/") .addConverterFactory(GsonConverterFactory.create()) .build(); GitHubService service = retrofit.create(GitHubService.class); Specify the base URL Add the JSON converter Implement the service
14. Making the Request // Asynchronous HTTP request to the remote webserver Call <List<Repo>> repos = service.listRepos(); call.enqueue(new Callback <List<Contributor>> () { @Override void onResponse(Response <List<Contributor>> contributors) { // Display some data } @Override void onFailure(Throwable t) { // Handle error } });
15. Path Parameters Dynamic URLs @GET("/users/{user}/repos") Call <List<GitHubRepo>> getReposUsingDynamicUrl(@Path("user") String user); // Fetch a list of GitHub repos Call <List<GitHubRepo>> call = service.getReposUsingDynamicUrl("pascalhow"); Very useful when interacting with app!
16. Query Parameters • Request data not part of URL • Not added to annotation URL like path parameters https://api.github.com/repos/jamescoggan/android-tech-talks-april/commits?author=pascalhow @GET("/repos/{user}/{repos}/commits") Call <List<Commit>> getCommits( @Path("user") String user, @Path("repos") String repos, @Query("author") String author);
17. Posting Data @POST("/commits") Call <Commit> createCommit(@Body Commit commit); public class Commit { private String author; private String message; // Getter and setter } Commit commit = new Commit("pascalhow", "Initial commit"); Call <Commit> call = GitHubService.createCommit(commit); call.enqueue(new Callback <Commit> () {}); { "author": "pascalhow", "message": "Initial commit" }
18. Authentication • What if an API call needs authorisation? • HTTP headers passes additional information with request or response • Use OkHttp to generate credentials
19. Authentication @GET("/user") Call<UserDetails> getUserDetails(@Header("Authorization") String credentials) • Generate the Auth Token with: Credentials.basic("username","password");
20. Authentication • What if we need to make several calls that all need authentication? Use Interceptors! • Interceptors are powerful mechanisms that can monitor, rewrite and retry calls
21. Authentication OkHttpClient httpClient = new OkHttpClient().Builder() .addInterceptor(new Interceptor() { @Override public Response intercept(Chain chain) throws IOException { Request originalRequest = chain.request(); Request.Builder builder = originalRequest.newBuilder() .header("Authorization", Credentials.basic("username", "password")); Request newRequest = builder.build(); return chain.proceed(newRequest); } }).build(); Add an interceptor to OkHttp Add credentials to the Authorisation header
22. Authentication Retrofit retrofit = new Retrofit.Builder() .baseUrl("https://api.example.com") .addConverterFactory(GsonConverterFactory.create()) .client(okHttpClient) .build(); Add our OkHttpClient to Retrofit!
23. Retrofit and RxJava • Retrofit supports RxJava! • Simplifies code further with lambdas • Good when making several network calls before updating UI
24. Retrofit and RxJava Add dependency to gradle compile 'com.squareup.retrofit2:adapter-rxjava:2.2.0' public interface GitHubService { @GET("/users/{user}/repos") Observable <List<GitHubRepo>> getReposUsingRxJava(@Path("user") String user); }
25. Retrofit and RxJava Retrofit retrofit = new Retrofit.Builder() .baseUrl("https://api.example.com") .addConverterFactory(GsonConverterFactory.create()) .addCallAdapterFactory(RxJavaCallAdapterFactory.create()) .client(okHttpClient) .build(); GitHubService service = retrofit.create(GitHubService.class); Add RxJava adapter to Retrofit!
26. Retrofit and RxJava service.getReposUsingRxJava(accountName) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Subscriber <List<GitHubRepo>> () { @Override public void onCompleted() { // Request completed } @Override public void onError(Throwable e) { // Handle error } @Override public void onNext(List < GitHubRepo > gitHubRepos) { displayData(gitHubRepos); } });
27. Conclusion • What Retrofit is • Implementing Retrofit in your Android app • Explored HTTP requests • Adding Authentication • Using Retrofit with RxJava
28. Any Questions?
29. Thank You! https://github.com/pascalhow https://www.linkedin.com/in/pascal-how-35b3133b/