官方文档：http://square.github.io/retrofit/
1.在AndroidManifest.xml中请求了网络权限：
<uses-permission android:name="android.permission.INTERNET"/>
2.添加Gradle依赖项：
compile 'com.squareup.retrofit2:retrofit:2.0.0-beta3'
compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta3'
compile 'com.squareup.retrofit2:adapter-rxjava:2.0.0-beta3'
compile 'io.reactivex:rxandroid:1.0.1'
Retrofit 支持许多种解析方式来解析响应数据:
Gson com.squareup.retrofit:converter-gson:2.0.0-beta2
Jackson com.squareup.retrofit:converter-jackson:2.0.0-beta1
Moshi com.squareup.retrofit:converter-moshi:2.0.0-beta1
Protobuf com.squareup.retrofit:converter-protobuf:2.0.0-beta1
Wire com.squareup.retrofit:converter-wire:2.0.0-beta1
Simple XML com.squareup.retrofit:converter-simplexml:2.0.0-beta1
3.创建API接口：
public interface GitHub {@GET("/repos/{owner}/{repo}/contributors")Call<List<Contributor>> contributors(@Path("owner") String owner,@Path("repo") String repo);}4.创建retrofit实例，并添加gson转换器：
public static final String API_URL = "https://api.github.com";
// Create a very simple REST adapter which points the GitHub API.
Retrofit retrofit = new Retrofit.Builder().baseUrl(API_URL).addConverterFactory(GsonConverterFactory.create()).build();5.创建一个Java类Contributor，用来保存接收到的数据:
public static class Contributor {public final String login;public final int contributions;public Contributor(String login, int contributions) {this.login = login;this.contributions = contributions;}
}6.调用API接口：
// Create an instance of our GitHub API interface.
GitHub github = retrofit.create(GitHub.class);// Create a call instance for looking up Retrofit contributors.
//完整的请求地址：https://api.github.com/repos/square/retrofit/contributors
Call<List<Contributor>> call = github.contributors("square", "retrofit");// Fetch and print a list of the contributors to the library.
List<Contributor> contributors = call.execute().body();
for (Contributor contributor : contributors) {System.out.println(contributor.login + " (" + contributor.contributions + ")");
}7.取消请求
我们可以终止一个请求。终止操作是对底层的httpclient执行cancel操作。即使是正在执行的请求，也能够立即终止。
call.cancel();
Retrofit与RxJava结合
1.使用Observable创建一个API接口：
public interface GitHub2 {@GET("/repos/{owner}/{repo}/contributors")Observable<List<Contributor>> contributors(@Path("owner") String owner,@Path("repo") String repo);}2.创建retrofit对象实例时，通过addCallAdapterFactory来添加对RxJava的支持：
Retrofit retrofit = new Retrofit.Builder().baseUrl(API_URL).addConverterFactory(GsonConverterFactory.create()).addCallAdapterFactory(RxJavaCallAdapterFactory.create()).build();3.调用API接口：
// Create an instance of our GitHub API interface.
GitHub2 github = retrofit.create(GitHub2.class);
Observable<List<Contributor>> observable = github.contributors("square", "retrofit");observable.subscribe(new Subscriber<List<Contributor>>() {@Overridepublic void onCompleted() {}@Overridepublic void onError(Throwable e) {}@Overridepublic void onNext(List<Contributor> contributors) {for (Contributor contributor : contributors) {System.out.println("observable " + contributor.login + " (" + contributor.contributions + ")");}}
});Retrofit使用OkHttp
OkHttpClient okHttpClient = new OkHttpClient.Builder().addInterceptor(new Interceptor() {@Overridepublic okhttp3.Response intercept(Chain chain) throws IOException {okhttp3.Response response = chain.proceed(chain.request());response.header(IF_MODIFIED_SINCE, "");return response;}}).build();
Retrofit retrofit = new Retrofit.Builder().baseUrl(HOST).addCallAdapterFactory(RxJavaCallAdapterFactory.create()).addConverterFactory(GsonConverterFactory.create()).client(okHttpClient).build();
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