Android 文件下載三種基本方式

一、自己封裝URLConnection 連接請求類

   public void downloadFile1() {
    try{
        //下載路徑，如果路徑無效了，可換成你的下載路徑
        String url = "http://c.qijingonline.com/test.mkv";
        String path = Environment.getExternalStorageDirectory().getAbsolutePath();

        final long startTime = System.currentTimeMillis();
        Log.i("DOWNLOAD","startTime="+startTime);
        //下載函數
       String filename=url.substring(url.lastIndexOf("/") + 1);
        //獲取文件名
        URL myURL = new URL(url);
        URLConnection conn = myURL.openConnection();
        conn.connect();
        InputStream is = conn.getInputStream();
        int fileSize = conn.getContentLength();//根據響應獲取文件大小
        if (fileSize <= 0) throw new RuntimeException("無法獲知文件大小 ");
        if (is == null) throw new RuntimeException("stream is null");
        File file1 = new File(path);
        if(!file1.exists()){
            file1.mkdirs();
        }
        //把數據存入路徑+文件名
        FileOutputStream fos = new FileOutputStream(path+"/"+filename);
        byte buf[] = new byte[1024];
        int downLoadFileSize = 0;
        do{
            //迴圈讀取
            int numread = is.read(buf);
            if (numread == -1)
            {
                break;
            }
            fos.write(buf, 0, numread);
            downLoadFileSize += numread;
            //更新進度條
        } while (true);

        Log.i("DOWNLOAD","download success");
        Log.i("DOWNLOAD","totalTime="+ (System.currentTimeMillis() - startTime));

        is.close();
    } catch (Exception ex) {
        Log.e("DOWNLOAD", "error: " + ex.getMessage(), ex);
    }
}

二、Android自定的下載管理（會在notification 顯示下載的進度，同時可以暫停、重新連接等）

private void downloadFile2(){
    //下載路徑，如果路徑無效了，可換成你的下載路徑
    String url = "http://c.qijingonline.com/test.mkv";
    //創建下載任務,downloadUrl就是下載鏈接
    DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
    //指定下載路徑和下載文件名
    request.setDestinationInExternalPublicDir("", url.substring(url.lastIndexOf("/") + 1));
    //獲取下載管理器
    DownloadManager downloadManager= (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
    //將下載任務加入下載隊列，否則不會進行下載
    downloadManager.enqueue(request);
}

 這種方式其實就是交給了Android系統的另一個app去下載管理。這樣的好處不會消耗該APP的 CPU資源。缺點是：控制起來很不靈活。

三、使用第三方 okhttp 網路請求框架

private void downloadFile3(){
    //下載路徑，如果路徑無效了，可換成你的下載路徑
    final String url = "http://c.qijingonline.com/test.mkv";
    final long startTime = System.currentTimeMillis();
    Log.i("DOWNLOAD","startTime="+startTime);

    Request request = new Request.Builder().url(url).build();
    new OkHttpClient().newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            // 下載失敗
            e.printStackTrace();
            Log.i("DOWNLOAD","download failed");
        }
        @Override
        public void onResponse(Call call, Response response) throws IOException {
            Sink sink = null;
            BufferedSink bufferedSink = null;
            try {
                String mSDCardPath= Environment.getExternalStorageDirectory().getAbsolutePath();
                File dest = new File(mSDCardPath,   url.substring(url.lastIndexOf("/") + 1));
                sink = Okio.sink(dest);
                bufferedSink = Okio.buffer(sink);
                bufferedSink.writeAll(response.body().source());

                bufferedSink.close();
                Log.i("DOWNLOAD","download success");
                Log.i("DOWNLOAD","totalTime="+ (System.currentTimeMillis() - startTime));
            } catch (Exception e) {
                e.printStackTrace();
                Log.i("DOWNLOAD","download failed");
            } finally {
                if(bufferedSink != null){
                    bufferedSink.close();
                }

            }
        }
    });
}

 public void downloadFile(){
        final String url = "http://c.qijingonline.com/test.mkv";
        final long startTime = System.currentTimeMillis();
        Log.i("DOWNLOAD","startTime="+startTime);
        OkHttpClient okHttpClient = new OkHttpClient();

        Request request = new Request.Builder().url(url).build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                // 下載失敗
                e.printStackTrace();
                Log.i("DOWNLOAD","download failed");
            }
            @Override
            public void onResponse(Call call, Response response) throws IOException {
                InputStream is = null;
                byte[] buf = new byte[2048];
                int len = 0;
                FileOutputStream fos = null;
                // 儲存下載文件的目錄
                String savePath = Environment.getExternalStorageDirectory().getAbsolutePath();
                try {
                    is = response.body().byteStream();
                    long total = response.body().contentLength();
                    File file = new File(savePath, url.substring(url.lastIndexOf("/") + 1));
                    fos = new FileOutputStream(file);
                    long sum = 0;
                    while ((len = is.read(buf)) != -1) {
                        fos.write(buf, 0, len);
                        sum += len;
                        int progress = (int) (sum * 1.0f / total * 100);
                        // 下載中
//                        listener.onDownloading(progress);
                    }
                    fos.flush();
                    // 下載完成
//                    listener.onDownloadSuccess();
                    Log.i("DOWNLOAD","download success");
                    Log.i("DOWNLOAD","totalTime="+ (System.currentTimeMillis() - startTime));
                } catch (Exception e) {
                    e.printStackTrace();
//                    listener.onDownloadFailed();
                    Log.i("DOWNLOAD","download failed");
                } finally {
                    try {
                        if (is != null)
                            is.close();
                    } catch (IOException e) {
                    }
                    try {
                        if (fos != null)
                            fos.close();
                    } catch (IOException e) {
                    }
                }
            }
        });
    }