Android 文件下载三种基本方式

一、自己封装URLConnection 连接请求类

   public void downloadFile1() {    try{        //下载路径，如果路径无效了，可换成你的下载路径        String url = "http://c.qijingonline.com/test.mkv";        String path = Environment.getExternalStorageDirectory().getAbsolutePath();        final long startTime = System.currentTimeMillis();        Log.i("DOWNLOAD","startTime="+startTime);        //下载函数       String filename=url.substring(url.lastIndexOf("/") + 1);        //获取文件名        URL myURL = new URL(url);        URLConnection conn = myURL.openConnection();        conn.connect();        InputStream is = conn.getInputStream();        int fileSize = conn.getContentLength();//根据响应获取文件大小        if (fileSize <= 0) throw new RuntimeException("无法获知文件大小 ");        if (is == null) throw new RuntimeException("stream is null");        File file1 = new File(path);        if(!file1.exists()){            file1.mkdirs();        }        //把数据存入路径+文件名        FileOutputStream fos = new FileOutputStream(path+"/"+filename);        byte buf[] = new byte[1024];        int downLoadFileSize = 0;        do{            //循环读取            int numread = is.read(buf);            if (numread == -1)            {                break;            }            fos.write(buf, 0, numread);            downLoadFileSize += numread;            //更新进度条        } 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);    }}

这种方式在Android 刚兴起的时候，很少下载封装框架，就自己封装了。虽然一般的文件都能下载，但这种方式缺点很多，不稳定或者各种各样的问题会出现。

 

二、Android自定的下载管理（会在notification 显示下载的进度，同时可以暂停、重新连接等）

private void downloadFile2(){    //下载路径，如果路径无效了，可换成你的下载路径    String url = "http://c.qijingonline.com/test.mkv";    //创建下载任务,downloadUrl就是下载链接    DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));    //指定下载路径和下载文件名    request.setDestinationInExternalPublicDir("", url.substring(url.lastIndexOf("/") + 1));    //获取下载管理器    DownloadManager downloadManager= (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);    //将下载任务加入下载队列，否则不会进行下载    downloadManager.enqueue(request);}

 这种方式其实就是交给了Android系统的另一个app去下载管理。这样的好处不会消耗该APP的 CPU资源。缺点是：控制起来很不灵活。

 

三、使用第三方 okhttp 网络请求框架

private void downloadFile3(){    //下载路径，如果路径无效了，可换成你的下载路径    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) {            // 下载失败            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();                }            }        }    });}

okhttp是一个很有名气的开源框架，目前已经很多大公司都直接使用它作为网络请求库（七牛云SDK， 阿里云SDK）。 且里面集成了很多优势，包括 okio (一个I/O框架，优化内存与CPU)。

 

在接收数据的时候使用了 okio框架 来做一些I/O处理，okio框架是弥补Java.io 上的不足，节省CPU与内存资源，但这个例子，我没还没看到其效果，也可以自己来接收字符流，然后获取下载的进度

 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) {                // 下载失败                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;                // 储存下载文件的目录                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);                        // 下载中//                        listener.onDownloading(progress);                    }                    fos.flush();                    // 下载完成//                    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) {                    }                }            }        });    }

 

 

 

 

综合来看，第三种方案是最佳的，是目前最流行的下载方案。