为大家分享了实现断点续传下载的具体代码，供大家参考，具体内容如下

1、基于Ok+Rxjava实现断点续传下载

2、基于Ok+Rxjava+Retrofit实现断点续传下载

上一篇博客中介绍了基于Ok+Rxjava实现断点续传下载，这一篇给大家介绍下基于Ok+Rxjava+Retrofit实现断点续传下载，demo下载地址，效果图跟上一篇图片一样，哈哈

说下我的大致思路吧（跟上一篇略有不同）:根据文件下载url按照自己定义的规则生成文件名，判断本地同路径下是否存在此文件，如果存在，文件大小与服务器上获取的文件大小一致的情况下，则覆盖本地文件重新下载；如果文件比服务器获取的文件大小小，则执行断点下载，从本地文件长度处开始下载。如果文件不存在，则从0字节开始下载。

还有的不同是，这里需要重新ResponseBody的source()方法，在这里监听文件下载的进度，然后通过我么自定义的Downloadinterceptor把我们重新的DownloadResponseBody给设置进去，从而完成我们的进度监听工作。

下面还是上主要代码：

首先重写ResponseBody

public class DownloadResponseBody extends ResponseBody { private ResponseBody responseBody;  //进度回调接口 private DownFileCallback downFileCallback;  private BufferedSource bufferedSource; private String downUrl;   public DownloadResponseBody(ResponseBody responseBody, DownFileCallback downFileCallback, String downUrl) { this.responseBody = responseBody; this.downFileCallback = downFileCallback; this.downUrl = downUrl; }  @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; File file = new File(DownloadManager.getInstance().getTemporaryName(downUrl));  @Override public long read(Buffer sink, long byteCount) throws IOException { long bytesRead = super.read(sink, byteCount); totalBytesRead += bytesRead != -1 ? bytesRead : 0; if (null != downFileCallback) { if (bytesRead != -1) { long loacalSize = file.length();//本地已下载的长度 long trueTotal = loacalSize + responseBody.contentLength() - totalBytesRead;//文件真实长度 downFileCallback.onProgress(trueTotal,loacalSize); } else {  }  } return bytesRead; } };  }}

重写Interceptor

public class Downloadinterceptor implements Interceptor {  private DownFileCallback downFileCallback;  private String downUrl;  public Downloadinterceptor(DownFileCallback listener,String downUrl) { this.downFileCallback = listener; this.downUrl = downUrl; }  @Override public Response intercept(Chain chain) throws IOException { Response response = chain.proceed(chain.request());  return response.newBuilder() .body(new DownloadResponseBody(response.body(), downFileCallback,downUrl)) .build(); }}

然后我们的service

public interface HttpService {  /*大文件需要加入Streaming这个判断，防止下载过程中写入到内存中,造成oom*/ @Streaming @GET Observable download(@Header("range") String start, @Url String url);}

接下来我们的DownloadManager中download方法

/** * 开始下载 * @param url 下载地址 * @param downFileCallback 进度回调接口 */ public void download(final String url, final DownFileCallback downFileCallback) { /*正在下载不处理*/ if (url == null || submap.get(url) != null) { return; }  Downloadinterceptor interceptor = new Downloadinterceptor(downFileCallback, url); okHttpClient = new OkHttpClient.Builder() .addInterceptor(interceptor) .build(); Retrofit retrofit = new Retrofit.Builder() .client(okHttpClient) .baseUrl("http://imtt.dd.qq.com") .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build(); final HttpService httpservice = retrofit.create(HttpService.class);  ProgressDownSubscriber subscriber = Observable.just(url) .flatMap(new Function>() { @Override public ObservableSource apply(String s) throws Exception { return Observable.just(createDownInfo(s)); } }) .map(new Function() { @Override public DownloadInfo apply(DownloadInfo s) throws Exception { return getRealFileName(s); } }) .flatMap(new Function>() { @Override public Observable apply(DownloadInfo downInfo) throws Exception { return httpservice.download("bytes=" + downInfo.getProgress() + "-", downInfo.getUrl()); } })//下载 .map(new Function() { @Override public DownloadInfo apply(ResponseBody responsebody) { try { return writecache(responsebody, url); } catch (IOException e) { //*失败抛出异常*// e.printStackTrace(); } return null; } }) .observeOn(AndroidSchedulers.mainThread())//在主线程回调 .subscribeOn(Schedulers.io())//在子线程执行 .subscribeWith(new ProgressDownSubscriber() { @Override public void onNext(DownloadInfo downInfo) { downFileCallback.onSuccess(downInfo); submap.remove(downInfo.getUrl()); }  @Override public void onError(Throwable t) { downFileCallback.onFail(t.getMessage()); submap.remove(url); } });   submap.put(url, subscriber); }

然后暂停操作：

/** * 暂停下载 */ public void stop(String url) { if (url == null) return; if (submap.containsKey(url)) { ProgressDownSubscriber subscriber = submap.get(url); subscriber.dispose(); submap.remove(url); } }

从服务器获取文件长度

/** * 从服务器获取文件长度 * * @param downloadUrl * @return */ private long getContentLength(String downloadUrl) { Request request = new Request.Builder() .url(downloadUrl) .build(); try { Response response = mClient.newCall(request).execute(); if (response != null && response.isSuccessful()) { long contentLength = response.body().contentLength(); response.close(); return contentLength == 0 ? DownloadInfo.TOTAL_ERROR : contentLength; } } catch (IOException e) { e.printStackTrace(); } return DownloadInfo.TOTAL_ERROR; }

从服务器获取文件长度的时候注意一下，Android P之后，也就是api 28以上禁止明文网络传输。需要在你的AndroidManifest中的application标签中声明"android:usesCleartextTraffic="true",允许应用进行明文传输。

使用方法：首先要获取sd卡权限

DownloadManager.getInstance().downloadPath(本地存放地址).download(url1, new DownFileCallback() { @Override public void onSuccess(DownloadInfo info) {  Toast.makeText(MainActivity.this, url1 + "下载完成", Toast.LENGTH_SHORT).show(); }  @Override public void onFail(String msg) { Toast.makeText(MainActivity.this, url1 + "下载失败", Toast.LENGTH_SHORT).show(); }  @Override public void onProgress(final long totalSize, final long downSize) { // 需要注意的是，如果文件总大小为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 // 好消息是，我已经在内部做过处理，放心使用吧，但是这个问题大家还是要知道的  runOnUiThread(new Runnable() { @Override public void run() { int progress = (int) (downSize * 100 / totalSize); progress1.setProgress(progress); } }); } });

好了今天就到这里，希望能帮到大家，这对我来说也是一种加深印象的笔记。

看完上述内容，你们掌握如何进行基于Ok+Rxjava+retrofit实现断点续传下载的方法了吗？如果还想学到更多技能或想了解更多相关内容，欢迎关注行业资讯频道，感谢各位的阅读！