项目中需要在开屏页下载东西，在github上发现一个好用的框架
大家可以去https://github.com/lingochamp/FileDownloader/blob/master/README-zh.md查看
关于retrofit的用法就不多说了，这个框架依赖于okhttp 3.4.1

  1. 首先在项目中引用
    compile 'com.liulishuo.filedownloader:library:0.3.4'
  2. 然后在Application的onCreate()中初始化
    FileDownloader.init(applicationContext);
  3. 在工具类中丢进这2个方法
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    /**
         * 单任务下载
         */
        public static void downloadFile(String path, String url) {
            FileDownloader.getImpl().create(url)
                    .setPath(path)
                    .setListener(new FileDownloadListener() {
                        @Override
                        protected void pending(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                        }

                        @Override
                        protected void connected(BaseDownloadTask task, String etag, boolean isContinue, int soFarBytes, int totalBytes) {
                        }

                        @Override
                        protected void progress(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                        }

                        @Override
                        protected void blockComplete(BaseDownloadTask task) {
                        }

                        @Override
                        protected void retry(final BaseDownloadTask task, final Throwable ex, final int retryingTimes, final int soFarBytes) {
                        }

                        @Override
                        protected void completed(BaseDownloadTask task) {
                        }

                        @Override
                        protected void paused(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                        }

                        @Override
                        protected void error(BaseDownloadTask task, Throwable e) {
                        }

                        @Override
                        protected void warn(BaseDownloadTask task) {
                        }
                    }).start();
        }

        /**
         * 多任务下载
         * 参数1：url的集合   参数2：下载的路径
         */

        public static void downloadFiles(List<RingListJson.RingBean> urls,File dir) {
            final FileDownloadListener downloadListener = new FileDownloadListener() {
                @Override
                protected void pending(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                }

                @Override
                protected void connected(BaseDownloadTask task, String etag, boolean isContinue, int soFarBytes, int totalBytes) {
                
                }

                @Override
                protected void progress(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                }

                @Override
                protected void blockComplete(BaseDownloadTask task) {
                }

                @Override
                protected void retry(final BaseDownloadTask task, final Throwable ex, final int retryingTimes, final int soFarBytes) {
                }

                @Override
                protected void completed(BaseDownloadTask task) {
                
                }

                @Override
                protected void paused(BaseDownloadTask task, int soFarBytes, int totalBytes) {
                }

                @Override
                protected void error(BaseDownloadTask task, Throwable e) {
                 }

                @Override
                protected void warn(BaseDownloadTask task) {
                }
            };

            final FileDownloadQueueSet queueSet = new FileDownloadQueueSet(downloadListener);

            final List<BaseDownloadTask> tasks = new ArrayList<>();
            for (int i = 0; i < urls.size(); i++) {
                if (FileDownloader.getImpl().create((urls.get(i).url)).isReusedOldFile()) {
                    continue;
                }

                tasks.add(FileDownloader.getImpl()
                        .create(urls.get(i).url)
                        .setTag(i + 1)
                        .setPath(dir.getAbsolutePath()+ File.separator+urls.get(i).name.concat(".aac")));

            }
        /*由于是队列任务, 这里是我们假设了现在不需要每个任务都回调`FileDownloadListener#progress`, 
          我们只关系每个任务是否完成, 
          所以这里这样设置可以很有效的减少ipc.*/
            queueSet.disableCallbackProgressTimes(); 

            // 所有任务在下载失败的时候都自动重试一次
            queueSet.setAutoRetryTimes(1);

            queueSet.downloadTogether(tasks);
            queueSet.start();

        }
  4. 在需要下载的地方调用者2个方法即可
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    Retrofit retrofit = new Retrofit.Builder().baseUrl("http:/xxx.xxx.com").addConverterFactory(GsonConverterFactory.create()).build();
            RingListResult ringListResult = retrofit.create(RingListResult.class);
            Call<RingListJson> call = ringListResult.getRings();
            
                final File dir = D8Application.applicationContext.getFilesDir();
                final File rings = new File(dir + "/rings");
                if (!rings.exists()) {
                    rings.mkdirs();
                }
            call.enqueue(new Callback<RingListJson>() {
                @Override
                public void onResponse(Call<RingListJson> call, Response<RingListJson> response) {
                    RingListJson ringListJson = response.body();
                    List<RingListJson.RingBean> ringList = ringListJson.ring; //在服务器拿到url的集合
                    Api.downloadFiles(ringList,rings);    //传进方法里  Api是自己的工具类
                }

                @Override
                public void onFailure(Call<RingListJson> call, Throwable t) {

                }
            });