Android OkHttp + Retrofit 下載文件與進度監聽
- 2019 年 10 月 19 日
- 筆記
下載文件是一個比較常見的需求。給定一個url，我們可以使用URLConnection下載文件。
使用OkHttp也可以通過流來下載文件。
給OkHttp中添加攔截器，即可實現下載進度的監聽功能。
使用流來實現下載文件
程式碼可以參考：https://github.com/RustFisher/android-Basic4/tree/master/appdowloadsample
獲取並使用位元組流，需要注意兩個要點，一個是服務介面方法的 @Streaming 註解，另一個是獲取到ResponseBody。
獲取流（Stream）。先定義一個服務ApiService。給方法添加上@Streaming的註解。
private interface ApiService { @Streaming @GET Observable<ResponseBody> download(@Url String url); }初始化OkHttp。記得填入你的baseUrl。
OkHttpClient okHttpClient = new OkHttpClient.Builder() .connectTimeout(8, TimeUnit.SECONDS) .build(); retrofit = new Retrofit.Builder() .client(okHttpClient) .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .baseUrl("https://yourbaseurl.com") .build();發起網路請求。獲取到ResponseBody。
String downUrl = "xxx.com/aaa.apk"; retrofit.create(ApiService.class) .download(downUrl) .subscribeOn(Schedulers.io()) .observeOn(Schedulers.io()) .doOnNext(new Consumer<ResponseBody>() { @Override public void accept(ResponseBody responseBody) throws Exception { // 處理 ResponseBody 中的流 } }) .doOnError(new Consumer<Throwable>() { @Override public void accept(Throwable throwable) throws Exception { Log.e(TAG, "accept on error: " + downUrl, throwable); } }) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Observer<ResponseBody>() { @Override public void onSubscribe(Disposable d) { } @Override public void onNext(ResponseBody responseBody) { } @Override public void onError(Throwable e) { Log.e(TAG, "Download center retrofit onError: ", e); } @Override public void onComplete() { } });通過ResponseBody拿到位元組流 body.byteStream()。這裡會先創建一個臨時文件tmpFile，把數據寫到臨時文件里。
下載完成後再重命名成目標文件targetFile。
public void saveFile(ResponseBody body) { state = DownloadTaskState.DOWNLOADING; byte[] buf = new byte[2048]; int len; FileOutputStream fos = null; try { Log.d(TAG, "saveFile: body content length: " + body.contentLength()); srcInputStream = body.byteStream(); File dir = tmpFile.getParentFile(); if (dir == null) { throw new FileNotFoundException("target file has no dir."); } if (!dir.exists()) { boolean m = dir.mkdirs(); onInfo("Create dir " + m + ", " + dir); } File file = tmpFile; if (!file.exists()) { boolean c = file.createNewFile(); onInfo("Create new file " + c); } fos = new FileOutputStream(file); long time = System.currentTimeMillis(); while ((len = srcInputStream.read(buf)) != -1 && !isCancel) { fos.write(buf, 0, len); int duration = (int) (System.currentTimeMillis() - time); int overBytes = len - downloadBytePerMs() * duration; if (overBytes > 0) { try { Thread.sleep(overBytes / downloadBytePerMs()); } catch (Exception e) { e.printStackTrace(); } } time = System.currentTimeMillis(); if (isCancel) { state = DownloadTaskState.CLOSING; srcInputStream.close(); break; } } if (!isCancel) { fos.flush(); boolean rename = tmpFile.renameTo(targetFile); if (rename) { setState(DownloadTaskState.DONE); onSuccess(url); } else { setState(DownloadTaskState.ERROR); onError(url, new Exception("Rename file fail. " + tmpFile)); } } } catch (FileNotFoundException e) { Log.e(TAG, "saveFile: FileNotFoundException ", e); setState(DownloadTaskState.ERROR); onError(url, e); } catch (Exception e) { Log.e(TAG, "saveFile: IOException ", e); setState(DownloadTaskState.ERROR); onError(url, e); } finally { try { if (srcInputStream != null) { srcInputStream.close(); } if (fos != null) { fos.close(); } } catch (IOException e) { Log.e(TAG, "saveFile", e); } if (isCancel) { onCancel(url); } } } 每次讀數據的循環，計算讀了多少數據和用了多少時間。超過限速後主動sleep一下，達到控制下載速度的效果。
要注意不能sleep太久，以免socket關閉。
這裡控制的是網路數據流與本地文件的讀寫速度。
下載進度監聽
OkHttp實現下載進度監聽，可以從位元組流的讀寫那裡入手。也可以使用攔截器，參考官方的例子。
這裡用攔截器的方式實現網路下載進度監聽功能。
定義回調與網路攔截器
先定義回調。
public interface ProgressListener { void update(String url, long bytesRead, long contentLength, boolean done); }自定義ProgressResponseBody。
public class ProgressResponseBody extends ResponseBody { private final ResponseBody responseBody; private final ProgressListener progressListener; private BufferedSource bufferedSource; private final String url; ProgressResponseBody(String url, ResponseBody responseBody, ProgressListener progressListener) { this.responseBody = responseBody; this.progressListener = progressListener; this.url = url; } @Override public MediaType contentType() { return responseBody.contentType(); } @Override public long contentLength() { return responseBody.contentLength(); } @Override public BufferedSource source() { if (bufferedSource == null) { bufferedSource = Okio.buffer(source(responseBody.source())); } return bufferedSource; } private Source source(final Source source) { return new ForwardingSource(source) { long totalBytesRead = 0L; @Override public long read(Buffer sink, long byteCount) throws IOException { long bytesRead = super.read(sink, byteCount); // read() returns the number of bytes read, or -1 if this source is exhausted. totalBytesRead += bytesRead != -1 ? bytesRead : 0; progressListener.update(url, totalBytesRead, responseBody.contentLength(), bytesRead == -1); return bytesRead; } }; } }定義攔截器。從Response中獲取資訊。
public class ProgressInterceptor implements Interceptor { private ProgressListener progressListener; public ProgressInterceptor(ProgressListener progressListener) { this.progressListener = progressListener; } @NotNull @Override public Response intercept(@NotNull Chain chain) throws IOException { Response originalResponse = chain.proceed(chain.request()); return originalResponse.newBuilder() .body(new ProgressResponseBody(chain.request().url().url().toString(), originalResponse.body(), progressListener)) .build(); } }添加攔截器
在創建OkHttpClient時添加ProgressInterceptor。
OkHttpClient okHttpClient = new OkHttpClient.Builder() .connectTimeout(8, TimeUnit.SECONDS) .addInterceptor(new ProgressInterceptor(new ProgressListener() { @Override public void update(String url, long bytesRead, long contentLength, boolean done) { // tellProgress(url, bytesRead, contentLength, done); } })) .build();值得注意的是這裡的進度更新非常頻繁。並不一定每次回調都要去更新UI。
