【Android架构】基于MVP模式的Retrofit2+RXjava封装之文件下载（二）

上篇中我们介绍了基于MVP的Retrofit2+RXjava封装，这一篇我们来说说文件下载的实现。

• 【Android架构】基于MVP模式的Retrofit2+RXjava封装（一）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之文件下载（二）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之文件上传（三）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之常见问题（四）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之断点下载（五）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之数据预处理（六）

我们先在ApiServer定义好调用的接口

@GET
    Observable<ResponseBody> downloadFile(@Url String fileUrl);
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接着定义一个接口，下载成功后用来回调

public interface FileView extends BaseView {

    void onSuccess(File file);
}
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接着是Observer，建议与处理普通接口的Observer区分处理

public abstract class FileObsever extends BaseObserver<ResponseBody> {
    private String path;

    public FileObsever(BaseView view, String path) {
        super(view);
        this.path = path;
    }

    @Override
    protected void onStart() {
    }

    @Override
    public void onComplete() {
    }

    @Override
    public void onSuccess(ResponseBody o) {

    }

    @Override
    public void onError(String msg) {

    }

    @Override
    public void onNext(ResponseBody o) {
        File file = FileUtil.saveFile(path, o);
        if (file != null && file.exists()) {
            onSuccess(file);
        } else {
            onErrorMsg("file is null or file not exists");
        }
    }

    @Override
    public void onError(Throwable e) {
        onErrorMsg(e.toString());
    }


    public abstract void onSuccess(File file);

    public abstract void onErrorMsg(String msg);
}

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FileUtil 注：如果需要写入文件的进度，可以在将这段方法放在onNext中，在FileObsever这个类写个方法，然后回调。

public static File saveFile(String filePath, ResponseBody body) {
        InputStream inputStream = null;
        OutputStream outputStream = null;
        File file = null;
        try {
            if (filePath == null) {
                return null;
            }
            file = new File(filePath);
            if (file == null || !file.exists()) {
                file.createNewFile();
            }


            long fileSize = body.contentLength();
            long fileSizeDownloaded = 0;
            byte[] fileReader = new byte[4096];

            inputStream = body.byteStream();
            outputStream = new FileOutputStream(file);

            while (true) {
                int read = inputStream.read(fileReader);
                if (read == -1) {
                    break;
                }
                outputStream.write(fileReader, 0, read);
                fileSizeDownloaded += read;

            }

            outputStream.flush();


        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return file;
    }
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下来是FilePresenter

public class FilePresenter extends BasePresenter<FileView> {
    public FilePresenter(FileView baseView) {
        super(baseView);
    }

    public void downFile(String url, final String path) {

        addDisposable(apiServer.downloadFile(url), new FileObsever(baseView, path) {


            @Override
            public void onSuccess(File file) {
                if (file != null && file.exists()) {
                    baseView.onSuccess(file);
                } else {
                    baseView.showError("file is null");
                }
            }

            @Override
            public void onErrorMsg(String msg) {
                baseView.showError(msg);

            }
        });

    }
    }
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最后在Activity中调用

private void downFile() {
        String url = "http://download.sdk.mob.com/apkbus.apk";

        String state = Environment.getExternalStorageState();
        if (state.equals(Environment.MEDIA_MOUNTED)) {// 检查是否有存储卡
            dir = Environment.getExternalStorageDirectory() + "/ceshi/";
            File dirFile = new File(dir);
            if (!dirFile.exists()) {
                dirFile.mkdirs();
            }
        }
        presenter.downFile(url, dir + "app-debug.apk");
    }
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就在我以为万事大吉的时候，APP崩溃了，错误信息如下： [图片上传失败...(image-39e2a7-1532052138950)]

原来是加入日志监听器，会导致每次都把整个文件加载到内存，那我们就去掉这个

修改FilePresenter#downFile如下：

public void downFile(String url, final String path) {

        OkHttpClient client = new OkHttpClient.Builder().build();
        Retrofit retrofit = new Retrofit.Builder().client(client)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .baseUrl("https://wawa-api.vchangyi.com/").build();

        apiServer = retrofit.create(ApiServer.class);

        addDisposable(apiServer.downloadFile(url), new FileObsever(baseView, path) {
            @Override
            public void onSuccess(File file) {
                if (file != null && file.exists()) {
                    baseView.onSuccess(file);
                } else {
                    baseView.showError("file is null");
                }
            }

            @Override
            public void onErrorMsg(String msg) {
                baseView.showError(msg);

            }
        });
    }
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这次倒是下载成功了，不过官方建议10M以上的文件用Streaming标签，我们加上Streaming标签试试 修改ApiServer

@Streaming
    @GET
    /**
     * 大文件官方建议用 @Streaming 来进行注解，不然会出现IO异常，小文件可以忽略不注入
     */
    Observable<ResponseBody> downloadFile(@Url String fileUrl);
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这次又崩溃了，错误信息如下： [图片上传失败...(image-fc8c28-1532052138951)]

这是怎么回事，我们网络请求是在子线程啊。无奈之下只得翻翻官方文档，原来使用该注解表示响应用字节流的形式返回.如果没使用该注解,默认会把数据全部载入到内存中。我们可以在主线程中处理写入文件（不建议），但不能在主线程中处理字节流。所以，我们需要将处理字节流、写入文件都放在子线程中。

于是，修改FilePresenter#downFile如下：

OkHttpClient client = new OkHttpClient.Builder().build();
        Retrofit retrofit = new Retrofit.Builder().client(client)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .baseUrl("https://wawa-api.vchangyi.com/").build();

        apiServer = retrofit.create(ApiServer.class);
          apiServer
                .downloadFile(url)
                .map(new Function<ResponseBody, String>() {
                    @Override
                    public String apply(ResponseBody body) throws Exception {
                        File file = FileUtil.saveFile(path, body);
                        return file.getPath();
                    }
                }).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(new FileObserver(baseView) {
                    @Override
                    public void onSuccess(File file) {
                        baseView.onSuccess(file);
                    }

                    @Override
                    public void onError(String msg) {
                        baseView.showError(msg);
                    }
                });
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这样，下载文件算是完成了，好像还缺点什么？对，缺个下载进度，还记得拦截器吗，我们可以从这里入手：

public class ProgressResponseBody extends ResponseBody {
    private ResponseBody responseBody;
    private BufferedSource bufferedSource;
    private ProgressListener progressListener;

    public ProgressResponseBody(ResponseBody responseBody, ProgressListener progressListener) {
        this.responseBody = responseBody;
        this.progressListener = progressListener;
    }


    @Nullable
    @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(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);
                totalBytesRead += bytesRead;
                progressListener.onProgress(responseBody.contentLength(), totalBytesRead);
                return bytesRead;
            }
        };
    }

    public interface ProgressListener {
        void onProgress(long totalSize, long downSize);
    }
}

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在BaseView 中定义接口，个人建议放在BaseView 中，在BaseActivity中实现BaseView，方便复用

/**
     * 下载进度
     *
     * @param totalSize
     * @param downSize
     */

    void onProgress(long totalSize, long downSize);
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再次修改FilePresenter#downFile如下：

public void downFile(final String url, final String path) {


        OkHttpClient client = new OkHttpClient.Builder()
                .addNetworkInterceptor(new Interceptor() {
                    @Override
                    public Response intercept(Chain chain) throws IOException {
                        Response response = chain.proceed(chain.request());
                        return response.newBuilder().body(new ProgressResponseBody(response.body(),
                                new ProgressResponseBody.ProgressListener() {
                                    @Override
                                    public void onProgress(long totalSize, long downSize) {
                                        baseView.onProgress(totalSize, downSize);
                                    }
                                })).build();
                    }
                }).build();

        Retrofit retrofit = new Retrofit.Builder().client(client)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .baseUrl("https://wawa-api.vchangyi.com/").build();

        apiServer = retrofit.create(ApiServer.class);

        apiServer
                .downloadFile(url)
                .map(new Function<ResponseBody, String>() {
                    @Override
                    public String apply(ResponseBody body) throws Exception {
                        File file = FileUtil.saveFile(path, body);
                        return file.getPath();
                    }
                }).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(new FileObserver(baseView) {
                    @Override
                    public void onSuccess(File file) {
                        baseView.onSuccess(file);
                    }

                    @Override
                    public void onError(String msg) {
                        baseView.showError(msg);
                    }
                });


    }
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至此，使用Retrofit下载文件暂时告一段落。