Android 网络通信API的选择和实现实例

　　Android开发网络通信一开始的时候使用的是AsyncTask封装HttpClient，没有使用原生的HttpURLConnection就跳到了Volley，随着OkHttp的流行又开始迁移到OkHttp上面，随着Rxjava的流行又了解了Retrofit，随着Retrofit的发展又从1.x到了2.x......。好吧，暂时到这里。

　　那么的多的使用工具有时候有点眼花缭乱，今天来总结一下现在比较流行的基于OkHttp 和 Retrofit 的网络通信API设计方法。有些同学可能要想，既然都有那么好用的Volley和Okhttp了，在需要用到的地方创建一个Request然后交给RequestQueue（Volley的方式）或者 Call（Okhttp的方式）就行了吗，为什么还那么麻烦？ 但是我认为这种野生的网络库的用法还是是有很多弊端（弊端就不说了，毕竟是总结新东西），在好的Android架构中都不会出现这样的代码。

　　网络通信都是异步完成，设计网络API我觉得首先需要考虑异步结果的返回机制。基于Okhttp或Retrofit，我们考虑如何返回异步的返回结果，有几种方式：

　　1. 直接返回：

　　OkHttp 的返回方式：

OkHttpClient : OkHttpClient client = new OkHttpClient();

Request :  Request request = new Request.Builder()
.url("https://api.github.com/repos/square/okhttp/issues")
.header("User-Agent", "OkHttp Headers.java")
.addHeader("Accept", "application/json; q=0.5")
.addHeader("Accept", "application/vnd.github.v3+json")
.build();

//第一种
Response response = client.newCall(request).execute();
// 第二种
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Request request, Throwable throwable) {

}
@Override public void onResponse(Response response) throws IOException {

}
}

　　Retrofit 的方式：

interface GitHubService {
@GET("/repos/{owner}/{repo}/contributors")
Call<List<Contributor>> repoContributors(
@Path("owner") String owner,
@Path("repo") String repo);
}
Call<List<Contributor>> call =
gitHubService.repoContributors("square", "retrofit");

response = call.execute();

　　上面的方式适用于野生的返回网络请求的内容。

　　2. 使用事件总线（Otto，EventBus，RxBus（自己使用PublishSubject封装））

　　代码来源：https://github.com/saulmm/Material-Movies

public interface MovieDatabaseAPI { /************Retrofit 1.x ，使用异步的方式返回 ****************/

@GET("/movie/popular")
void getPopularMovies(
@Query("api_key") String apiKey,
Callback<MoviesWrapper> callback);

@GET("/movie/{id}")
void getMovieDetail (
@Query("api_key") String apiKey,
@Path("id") String id,
Callback<MovieDetail> callback
);

@GET("/movie/popular")
void getPopularMoviesByPage(
@Query("api_key") String apiKey,
@Query("page") String page,
Callback<MoviesWrapper> callback
);

@GET("/configuration")
void getConfiguration (
@Query("api_key") String apiKey,
Callback<ConfigurationResponse> response
);

@GET("/movie/{id}/reviews")
void getReviews (
@Query("api_key") String apiKey,
@Path("id") String id,
Callback<ReviewsWrapper> response
);

@GET("/movie/{id}/images")
void getImages (
@Query("api_key") String apiKey,
@Path("id") String movieId,
Callback<ImagesWrapper> response
);
}

　　

public class RestMovieSource implements RestDataSource {

private final MovieDatabaseAPI moviesDBApi;
private final Bus bus; /***********使用了Otto**************/

public RestMovieSource(Bus bus) {

RestAdapter movieAPIRest = new RestAdapter.Builder() /*** Retrofit 1.x ***/
.setEndpoint(Constants.MOVIE_DB_HOST)
.setLogLevel(RestAdapter.LogLevel.HEADERS_AND_ARGS)
.build();

moviesDBApi = movieAPIRest.create(MovieDatabaseAPI.class);
this.bus = bus;
}

@Override
public void getMovies() {

moviesDBApi.getPopularMovies(Constants.API_KEY, retrofitCallback);
}

@Override
public void getDetailMovie(String id) {

moviesDBApi.getMovieDetail(Constants.API_KEY, id,
retrofitCallback);
}

@Override
public void getReviews(String id) {

moviesDBApi.getReviews(Constants.API_KEY, id,
retrofitCallback);
}

@Override
public void getConfiguration() {

moviesDBApi.getConfiguration(Constants.API_KEY, retrofitCallback);
}

@Override
public void getImages(String movieId) {

moviesDBApi.getImages(Constants.API_KEY, movieId,
retrofitCallback);
}

public Callback retrofitCallback = new Callback() { /******************这里统一的Callback，根据不同的返回值使用事件总线进行返回**************************/
@Override
public void success(Object o, Response response) {

if (o instanceof MovieDetail) {

MovieDetail detailResponse = (MovieDetail) o;
bus.post(detailResponse);

} else if (o instanceof MoviesWrapper) {

MoviesWrapper moviesApiResponse = (MoviesWrapper) o;
bus.post(moviesApiResponse);

} else if (o instanceof ConfigurationResponse) {

ConfigurationResponse configurationResponse = (ConfigurationResponse) o;
bus.post(configurationResponse);

} else if (o instanceof ReviewsWrapper) {

ReviewsWrapper reviewsWrapper = (ReviewsWrapper) o;
bus.post(reviewsWrapper);

} else if (o instanceof ImagesWrapper) {

ImagesWrapper imagesWrapper = (ImagesWrapper) o;
bus.post(imagesWrapper);
}
}

@Override
public void failure(RetrofitError error) {

System.out.printf("[DEBUG] RestMovieSource failure - " + error.getMessage());
}
};

@Override
public void getMoviesByPage(int page) {

moviesDBApi.getPopularMoviesByPage(
Constants.API_KEY,
page + "",
retrofitCallback
);
}
}

　　

　　3. 返回Observable（这里也可以考虑直接返回Observable 和间接返回Observable）

　　直接的返回 Observable，在创建 apiService 的时候使用 Retrofit.create(MovieDatabaseAPI)就行了（见下面代码）

public interface MovieDatabaseAPI {

@GET("/movie/popular")
Observable<MovieWrapper> getPopularMovies(
@Query("api_key") String apiKey,
);

@GET("/movie/{id}")
Observable<MovideDetail> getMovieDetail (
@Query("api_key") String apiKey,
@Path("id") String id,
);
}　　

　　间接返回Observable，这里参考了AndroidCleanArchitecture：

public interface RestApi {   /************定义API接口*****************/
String API_BASE_URL = "http://www.android10.org/myapi/";

/** Api url for getting all users */
String API_URL_GET_USER_LIST = API_BASE_URL + "users.json";
/** Api url for getting a user profile: Remember to concatenate id + 'json' */
String API_URL_GET_USER_DETAILS = API_BASE_URL + "user_";

/**
* Retrieves an {@link rx.Observable} which will emit a List of {@link UserEntity}.
*/
Observable<List<UserEntity>> userEntityList();

/**
* Retrieves an {@link rx.Observable} which will emit a {@link UserEntity}.
*
* @param userId The user id used to get user data.
*/
Observable<UserEntity> userEntityById(final int userId);
}

　　

/**** 使用Rx Observable 实现 RestApi 接口，实际调用的是 ApiConnection 里面的方法  ****/
public class RestApiImpl implements RestApi { /***注意这里没有使用Retrofit，而是对上面接口的实现***/

private final Context context;
private final UserEntityJsonMapper userEntityJsonMapper;

/**
* Constructor of the class
*
* @param context {@link android.content.Context}.
* @param userEntityJsonMapper {@link UserEntityJsonMapper}.
*/
public RestApiImpl(Context context, UserEntityJsonMapper userEntityJsonMapper) {
if (context == null || userEntityJsonMapper == null) {
throw new IllegalArgumentException("The constructor parameters cannot be null!!!");
}
this.context = context.getApplicationContext();
this.userEntityJsonMapper = userEntityJsonMapper;
}

@RxLogObservable(SCHEDULERS)
@Override
public Observable<List<UserEntity>> userEntityList() {
return Observable.create(subscriber -> {
if (isThereInternetConnection()) {
try {
String responseUserEntities = getUserEntitiesFromApi();
if (responseUserEntities != null) {
subscriber.onNext(userEntityJsonMapper.transformUserEntityCollection(
responseUserEntities));
subscriber.onCompleted();
} else {
subscriber.onError(new NetworkConnectionException());
}
} catch (Exception e) {
subscriber.onError(new NetworkConnectionException(e.getCause()));
}
} else {
subscriber.onError(new NetworkConnectionException());
}
});
}

@RxLogObservable(SCHEDULERS)
@Override
public Observable<UserEntity> userEntityById(final int userId) {
return Observable.create(subscriber -> {
if (isThereInternetConnection()) {
try {
String responseUserDetails = getUserDetailsFromApi(userId);
if (responseUserDetails != null) {
subscriber.onNext(userEntityJsonMapper.transformUserEntity(responseUserDetails));
subscriber.onCompleted();
} else {
subscriber.onError(new NetworkConnectionException());
}
} catch (Exception e) {
subscriber.onError(new NetworkConnectionException(e.getCause()));
}
} else {
subscriber.onError(new NetworkConnectionException());
}
});
}

private String getUserEntitiesFromApi() throws MalformedURLException {
return ApiConnection.createGET(RestApi.API_URL_GET_USER_LIST).requestSyncCall();
}

private String getUserDetailsFromApi(int userId) throws MalformedURLException {
String apiUrl = RestApi.API_URL_GET_USER_DETAILS + userId + ".json";
return ApiConnection.createGET(apiUrl).requestSyncCall();
}

/**
* Checks if the device has any active internet connection.
*
* @return true device with internet connection, otherwise false.
*/
private boolean isThereInternetConnection() {
boolean isConnected;

ConnectivityManager connectivityManager =
(ConnectivityManager) this.context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
isConnected = (networkInfo != null && networkInfo.isConnectedOrConnecting());

return isConnected;
}
}

　　

public class ApiConnection implements Callable<String> {  /***********************网络接口的实际实现********************************/

private static final String CONTENT_TYPE_LABEL = "Content-Type";
private static final String CONTENT_TYPE_VALUE_JSON = "application/json; charset=utf-8";

private URL url;
private String response;

private ApiConnection(String url) throws MalformedURLException {
this.url = new URL(url);
}

public static ApiConnection createGET(String url) throws MalformedURLException {
return new ApiConnection(url);
}

/**
* Do a request to an api synchronously.
* It should not be executed in the main thread of the application.
*
* @return A string response
*/
@Nullable
public String requestSyncCall() {
connectToApi();
return response;
}

private void connectToApi() {
OkHttpClient okHttpClient = this.createClient(); /*******************使用OKhttp的实现*******************/
final Request request = new Request.Builder()
.url(this.url)
.addHeader(CONTENT_TYPE_LABEL, CONTENT_TYPE_VALUE_JSON)
.get()
.build();

try {
this.response = okHttpClient.newCall(request).execute().body().string();
} catch (IOException e) {
e.printStackTrace();
}
}

private OkHttpClient createClient() {
final OkHttpClient okHttpClient = new OkHttpClient();
okHttpClient.setReadTimeout(10000, TimeUnit.MILLISECONDS);
okHttpClient.setConnectTimeout(15000, TimeUnit.MILLISECONDS);

return okHttpClient;
}

@Override
public String call() throws Exception {
return requestSyncCall();
}
}

　　这里简单总结了一下OkHttp和Retrofit该如何封装，这样的封装放在整个大的代码框架中具有很好的模块化效果。对于使用MVP架构或者类似架构的APP，良好的网络接口模块封装是非常重要的。