RxJava和retrofit实现多线程下载

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一直感慨RxJava在线程切换时很强大，最近项目中使用到了下载的功能，就想结合Retrofit来做一下这方面的尝试。

场景很简单，服务器提供3个文件的下载地址。客户端点击按钮去异步下载这些文件。这就涉及到多线程下载。

Retrofit部分：

BaseApi：

/** * songwenju on 16-8-5 : 16 : 09. * 邮箱：songwenju@outlook.com */public class BaseApi {    //统一的超时时间管理    public static OkHttpClient mOkHttpClient = new OkHttpClient.Builder()            .readTimeout(AppConstant.READ_TIMEOUT, TimeUnit.SECONDS)//设置读取超时时间            .writeTimeout(AppConstant.WRITE_TIMEOUT,TimeUnit.SECONDS)//设置写的超时时间            .connectTimeout(AppConstant.CONNECT_TIMEOUT,TimeUnit.SECONDS)//设置连接超时时间            .build();}

DownloadApi：这里是一个单例的，结合了懒汉式和饿汉式的特性，它是线程安全且只有一个实例

/** * songwenju on 16-8-23 : 16 : 32. * 邮箱：songwenju@outlook.com */public class DownloadApi extends BaseApi{    //单例的DownloadApi    private static DownloadApi mDownloadApi = new DownloadApi();    private DownloadService mDownloadService;    public static DownloadApi getInstance(){        return mDownloadApi;    }    private DownloadApi(){        Retrofit retrofit = new  Retrofit.Builder()                .client(mOkHttpClient)                .baseUrl(AppConstant.BASE_URL)                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())                .build();        mDownloadService = retrofit.create(DownloadService.class);    }    public DownloadService getDownloadService() {        return mDownloadService;    }}

DownloadService：这里使用了Streaming注解，该注解的作用是在下载大文件中使用。添加了该注解后，下载文件不会将所有的下载内容加载到内存。

/** * songwenju on 16-8-23 : 16 : 32. * 邮箱：songwenju@outlook.com */public interface DownloadService {   @Streaming   @GET   Observable<ResponseBody> downloadFile(@Url String fileUrl);}

WriteFileManager:将获得ResponseBody的内容写入到文件中。

/** * 写入文件管理类 */public class WriteFileManager {    private static final String TAG = "DownLoadManager";    public static boolean writeResponseBodyToDisk(ResponseBody body,String downloadName) {        String path = FileUtil.getVideoPath() + downloadName;        LogUtil.i(TAG, "WriteFileManager.startToWrite.path:" + path);        File futureFile = new File(path);        InputStream inputStream = null;        OutputStream outputStream = null;        long fileSize = body.contentLength();        LogUtil.d(TAG,"WriteFileManager.writeResponseBodyToDisk.fileSize:"+fileSize);        try {            try {                byte[] fileReader = new byte[1024 * 1024];                long fileSizeDownloaded = 0;                inputStream = body.byteStream();                outputStream = new FileOutputStream(futureFile);                while (true) {                    int read = inputStream.read(fileReader);                    if (read == -1) {                        break;                    }                    outputStream.write(fileReader, 0, read);                    fileSizeDownloaded += read;//                    LogUtil.i(TAG, "file download: " + fileSizeDownloaded + " of " + fileSize);                }                LogUtil.d(TAG, "file download: " + fileSizeDownloaded + " of " + fileSize);                outputStream.flush();                return true;            } catch (IOException e) {                e.printStackTrace();                return false;            } finally {                if (inputStream != null) {                    inputStream.close();                }                if (outputStream != null) {                    outputStream.close();                }            }        } catch (IOException e) {            return false;        }    }}

在activity中：这里使用merge去将observable合并。

public class MainActivity extends AppCompatActivity {    private DownloadService mDownloadService;    private List<String> mDownloadList;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        DownloadApi downloadApi = DownloadApi.getInstance();        mDownloadService = downloadApi.getDownloadService();        final String downloadUrl1 = AppConstant.DOWNLOAD_URL1;        final String downloadUrl2 = AppConstant.DOWNLOAD_URL2;        final String downloadUrl3 = AppConstant.DOWNLOAD_URL3;        mDownloadList = new ArrayList<>();        mDownloadList.add(downloadUrl1);        mDownloadList.add(downloadUrl2);        mDownloadList.add(downloadUrl3);    }    /**     * 多线程下载     * @param view view     */    public void download(View view) {        LogUtil.i(this, "MainActivity.download.");        List<Observable<Boolean>> observables = new ArrayList<Observable<Boolean>>();        //将所有的Observable放到List中        for (int i = 0; i < mDownloadList.size(); i++) {            final String downloadUrl = mDownloadList.get(i);            observables.add(mDownloadService.downloadFile(downloadUrl)                    .subscribeOn(Schedulers.io())                    .map(new Func1<ResponseBody, Boolean>() {                        @Override                        public Boolean call(ResponseBody responseBody) {                            return WriteFileManager.writeResponseBodyToDisk(responseBody, downloadUrl);                        }                    }).subscribeOn(Schedulers.io()));        }        //Observable的merge将所有的Observable合成一个Observable,所有的observable同时发射数据。        Observable.merge(observables).observeOn(AndroidSchedulers.mainThread())                .subscribe(new Subscriber<Boolean>() {                    @Override                    public void onCompleted() {                    }                    @Override                    public void onError(Throwable e) {                        e.printStackTrace();                    }                    @Override                    public void onNext(Boolean b) {                        if (b) {                            Toast.makeText(MainActivity.this, "Download is sucess", Toast.LENGTH_LONG).show();                        }                    }                });    }}

打出的log：

01-09 05:24:04.474 28625-28625/? I/swj_htv_MainActivity: MainActivity.download.01-09 05:24:04.574 28625-28786/? I/swj_htv_DownLoadManager: DownloadManager.startToWrite.path:/storage/emulated/0/Movies/mvp.wmv01-09 05:24:04.575 28625-28786/? D/swj_htv_DownLoadManager: DownloadManager.writeResponseBodyToDisk.fileSize:40093722301-09 05:24:04.575 28625-28785/? I/swj_htv_DownLoadManager: DownloadManager.startToWrite.path:/storage/emulated/0/Movies/chess.mp401-09 05:24:04.575 28625-28785/? D/swj_htv_DownLoadManager: DownloadManager.writeResponseBodyToDisk.fileSize:636663301-09 05:24:04.575 28625-28784/? I/swj_htv_DownLoadManager: DownloadManager.startToWrite.path:/storage/emulated/0/Movies/protein.mp401-09 05:24:04.575 28625-28784/? D/swj_htv_DownLoadManager: DownloadManager.writeResponseBodyToDisk.fileSize:37408153301-09 05:24:06.039 28625-28785/? D/swj_htv_DownLoadManager: file download: 6366633 of 636663301-09 05:25:12.286 28625-28784/? D/swj_htv_DownLoadManager: file download: 374081533 of 37408153301-09 05:25:14.302 28625-28786/? D/swj_htv_DownLoadManager: file download: 400937223 of 400937223

项目对应的demo已经上传到github上：

RxJavaRetrofitDownload

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