【Android架构】基于MVP模式的Retrofit2+RXjava封装之断点下载（五）

前言：最近有个断点下载的需求，捣鼓了下，而后分享下

• 【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）
• 【Android架构】基于MVP模式的Retrofit2+RXjava封装之多Url（七）

关于文件下载，在第2篇中已经详细说过，这里就不在详细说了，先对以前的下载作个封装 首先是ApiServer

@Streaming
   @GET
   /** * 大文件官方建议用 @Streaming 来进行注解，否则会出现IO异常，小文件能够忽略不注入 */
   Observable<ResponseBody> downloadFile(@Url String fileUrl);
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定义下载回调

public interface DownFileCallback {

    void onSuccess(String path);

    void onFail(String msg);

    void onProgress(long totalSize, long downSize);
}
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DownLoadManager

public class DownLoadManager {

    private static DownLoadManager loadManager;

    private HashMap<String, FileObserver> hashMap;
    private OkHttpClient client;
    private Retrofit retrofit;
    private ApiServer apiServer;
    private DownFileCallback fileCallback;
   


    public DownLoadManager() {
        hashMap = new HashMap<>();
        client = new OkHttpClient.Builder()
                .addNetworkInterceptor(new Interceptor() {
                    @Override
                    public Response intercept(Chain chain) throws IOException {

                        Request request = chain.request();
 
                       Response response = chain.proceed(request);
                        return response.newBuilder().body(new ProgressResponseBody(response.body(),
                                new ProgressResponseBody.ProgressListener() {
                                    @Override
                                    public void onProgress(long totalSize, long downSize) {
                                        if (fileCallback != null) {
                                            fileCallback.onProgress(totalSize, downSize);
                                        }
                                    }
                                })).build();
                    }
                }).build();
        retrofit = new Retrofit.Builder().client(client)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .baseUrl("https://wawa-api.vchangyi.com/").build();
        apiServer = retrofit.create(ApiServer.class);
    }

    public static DownLoadManager getInstance() {
        synchronized (Object.class) {
            if (loadManager == null) {
                loadManager = new DownLoadManager();
            }
        }
        return loadManager;
    }

 /** * 下载单个文件 * * @param url * @param fileCallback */
    public void downFile(final String url, final DownFileCallback fileCallback) {
        //若是正在下载，则暂停
        if (isDownLoad(url)) {
            pause(url);
            return;
        }
        this.fileCallback = fileCallback;
        //存储的文件路径
        final String path = getTemporaryName(url);

        FileObserver observer = 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<String>() {
                    @Override
                    public void onSuccess(String path) {

                        fileCallback.onSuccess(path);
                        hashMap.remove(url);
                    }

                    @Override
                    public void onError(String msg) {
                        fileCallback.onFail(msg);
                        hashMap.remove(url);
                    }
                });
        //保存
        hashMap.put(url, observer);
    }
 /** * 暂停/取消任务 * * @param url 完整url */
    public void pause(String url) {
        if (hashMap.containsKey(url)) {
            FileObserver observer = hashMap.get(url);
            if (observer != null) {
                observer.dispose();
                hashMap.remove(url);
            }
        }
    }

    /** * 获取临时文件名 * * @param url * @return */
    public static String getTemporaryName(String url) {
        String type = "";
        if (url.contains(".")) {
            type = url.substring(url.lastIndexOf("."));
        }
        String dirName = Environment.getExternalStorageDirectory() + "/mvp/";

        File f = new File(dirName);
        //不存在建立
        if (!f.exists()) {
            f.mkdirs();
        }
        return dirName + System.currentTimeMillis() + type;
    }


    /** * 是否在下载 * * @param url * @return */
    public boolean isDownLoad(String url) {
        return hashMap.containsKey(url);
    }


    public abstract class FileObserver<T> extends DisposableObserver<T> {

        @Override
        public void onNext(T t) {
            onSuccess(t);
        }

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

        @Override
        public void onComplete() {

        }


        public abstract void onSuccess(T o);

        public abstract void onError(String msg);
    }
}
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断点下载的话，有2点要注意

• 1.要添加RANGE请求头

if (downSize != 0 && totalSize != 0) {
                            request = request.newBuilder()
                                    .addHeader("RANGE", "bytes=" + downSize + "-" + totalSize).build();
                        }
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downSize和totalSize，前者是下载的开始长度，后者是整个文件的长度，这些都须要咱们暂停时，本身作保存。

• 2.写文件问题，断点下载时，就不能从头开始写入文件，须要从上次结束的地方开始，这里就用到了RandomAccessFile

/** * @param filePath * @param start 起始位置 * @param body */
    public static File saveFile(String filePath, long start, ResponseBody body) {
        InputStream inputStream = null;
        RandomAccessFile raf = null;
        File file = null;
        try {
            file = new File(filePath);

            raf = new RandomAccessFile(filePath, "rw");
            inputStream = body.byteStream();
            byte[] fileReader = new byte[4096];
            //移动到该位置
            raf.seek(start);

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


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

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

        return file;

    }
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建个实体类，来保存文件相关属性，get和set就不贴了

public class DownModel {

    private String url;
    private String path;
    private String title;
    private String cover;
    private long totalSize;
    private long currentTotalSize;
    private long downSize;
    private boolean isExists;
    private boolean isFinish;
    private boolean isPause;
}
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/** * 下载单个文件 * * @param downModel * @param */
    public void downFile(final DownModel downModel, final DownFileCallback fileCallback) {
        if (downModel == null) {
            return;
        }
        //若是正在下载，则暂停
        final String url = downModel.getUrl();
        if (isDownLoad(url)) {
            pause(url);
            Log.e("cheng", "pause url=" + url);
            return;
        }
        //当前连接
        currentUrl = url;
        //是不是断点下载
        if (downModel.getDownSize() != 0 && downModel.getTotalSize() != 0) {
            totalSize = downModel.getTotalSize();
            downSize = downModel.getDownSize();
            currentPath = downModel.getPath();
        } else {
            totalSize = 0;
            downSize = 0;
            currentPath = getTemporaryName(url);
            downModel.setPath(currentPath);
        }

        this.fileCallback = fileCallback;

        Log.e("cheng", "currentUrl=" + currentUrl);

        Log.e("cheng", "downSize=" + downSize + ",totalSize=" + totalSize + ",currentPath=" + currentPath);

        FileObserver observer = apiServer.downloadFile(url).map(new Function<ResponseBody, String>() {
            @Override
            public String apply(ResponseBody body) throws Exception {

                if (downModel.getDownSize() != 0 && downModel.getTotalSize() != 0) {
                    return FileUtil.saveFile(currentPath, downModel.getDownSize(), body).getPath();
                }
                File file = FileUtil.saveFile(currentPath, body);
                return file.getPath();
            }
        }).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(new FileObserver<String>() {
                    @Override
                    public void onSuccess(String path) {
                        downModel.setFinish(true);
                        downModel.setPath(path);
                        downModel.setExists(true);


                        if (fileCallback != null) {
                            fileCallback.onSuccess(path);
                        }
                        hashMap.remove(url);

                        currentUrl = null;
                    }

                    @Override
                    public void onError(String msg) {
                        if (fileCallback != null) {
                            fileCallback.onFail(msg);
                        }
                        hashMap.remove(url);
                        currentUrl = null;
                    }
                });
        //保存
        hashMap.put(url, observer);
    }
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须要注意的是，若是文件总大小为50M，已下载的大小为10M，再次下载时onProgress返回的totalSize是文件总长度 减去 已下载大小 10M， 即40M，downSize为本次下载的已下载量

private void down2() {
       String url = "http://download.sdk.mob.com/apkbus.apk";
       if (downModel == null) {
           downModel = new DownModel();
           downModel.setUrl(url);
       }
       DownLoadManager.getInstance().downFile(downModel, new DownFileCallback() {
           @Override
           public void onSuccess(String path) {
               showtoast("下载成功，path=" + path);
           }

           @Override
           public void onFail(String msg) {

           }

           @Override
           public void onProgress(long totalSize, long downSize) {
               Log.e("cheng", "totalSize =" + totalSize + ",downSize=" + downSize);
               if (downModel.getTotalSize() == 0) {
                   downModel.setTotalSize(totalSize);
               }
               downModel.setCurrentTotalSize(totalSize);

               downModel.setDownSize(downSize + downModel.getTotalSize() - downModel.getCurrentTotalSize());

               runOnUiThread(new Runnable() {
                   @Override
                   public void run() {
                       int progress = (int) (downModel.getDownSize() * 100 / downModel.getTotalSize());
                       tvDown.setText(progress + "%");
                       sbDown.setProgress(progress);
                   }
               });


           }
       });
   }
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最后，献上源码 Github

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