关于android:Android入门教程-OkHttp-Retrofit-下载文件与进度监听

下载文件是一个比拟常见的需要。给定一个 url，咱们能够应用 URLConnection 下载文件。应用 OkHttp 也能够通过流来下载文件。给 OkHttp 中增加拦截器，即可实现下载进度的监听性能。

应用流来实现下载文件

获取并应用字节流，须要留神两个要点，一个是服务接口办法的 @Streaming 注解，另一个是获取到 ResponseBody。

获取流（Stream）。先定义一个服务 ApiService。给办法增加上 @Streaming 的注解。

private interface ApiService {
        @Streaming
        @GET
        Observable<ResponseBody> download(@Url String url);
    }

初始化 OkHttp。记得填入你的 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();

发动网络申请。获取到 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 {// 解决 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() {}
            });

通过 ResponseBody 拿到字节流 body.byteStream()。这里会先创立一个临时文件 tmpFile，把数据写到临时文件里。下载实现后再重命名成指标文件 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);
            }
        }
    }

每次读数据的循环，计算读了多少数据和用了多少工夫。超过限速后被动 sleep 一下，达到管制下载速度的成果。要留神不能 sleep 太久，免得 socket 敞开。这里管制的是网络数据流与本地文件的读写速度。

下载进度监听

OkHttp 实现下载进度监听，能够从字节流的读写那里动手。也能够应用拦截器，参考官网的例子。这里用拦截器的形式实现网络下载进度监听性能。

定义回调与网络拦截器

先定义回调。

public interface ProgressListener {void update(String url, long bytesRead, long contentLength, boolean done);
}

自定义 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;
            }
        };
    }
}

定义拦截器。从 Response 中获取信息。

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();}
}

增加拦截器

在创立 OkHttpClient 时增加 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();

值得注意的是这里的进度更新十分频繁。并不一定每次回调都要去更新 UI。

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