1. 自己封裝URLConnection 連接請求類

這種方式在Android 剛興起的時候，很少下載封裝框架，就自己封裝了。雖然一般的文件都能下載，但這種方式缺點很多，不穩定或者各種各樣的問題會出現。

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{//循環讀取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);} }

2. 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.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。

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); }

3. 使用第三方 okhttp 網絡請求框架(推薦)

okhttp是一個很有名氣的開源框架，目前已經很多大公司都直接使用它作為網絡請求庫（七牛云SDK， 阿里云SDK）。 且里面集成了很多優勢，包括 okio (一個I/O框架，優化內存與CPU)。

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() {@Overridepublic void onFailure(Call call, IOException e) {// 下載失敗e.printStackTrace();Log.i("DOWNLOAD","download failed");}@Overridepublic 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();}}}}); }

在接收數據的時候使用了 okio框架 來做一些I/O處理，okio框架是彌補Java.io 上的不足，節省CPU與內存資源.
demo:

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() {@Overridepublic void onFailure(Call call, IOException e) {// 下載失敗e.printStackTrace();Log.i("DOWNLOAD","download failed");}@Overridepublic 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) {}}}});}

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