Android 利用OkHttp进行文件下载操作

上回我的博客中讲了如何使用OkHttp封装一套自己的网路请求框架，这次说说文件下载。其实我们APP中还是很多地方会用到文件下载的。比如版本更新的时候，比如图片本地缓存的时候，都会用到文件下载，那么我们如何使用这个功能呢?

首先我们要引入框架

implementation 'com.squareup.okhttp3:okhttp:3.6.0'

接着创建类DownloadUtil.java，内容如下

public class DownloadUtil {
    private static DownloadUtil downloadUtil;
    private final OkHttpClient okHttpClient;

    public static DownloadUtil get() {
        if (downloadUtil == null) {
            downloadUtil = new DownloadUtil();
        }
        return downloadUtil;
    }

    private DownloadUtil() {
        okHttpClient = new OkHttpClient();
    }

    /**
     * @param url 下载连接
     * @param saveDir 储存下载文件的SDCard目录
     * @param listener 下载监听
     */
    public void download(final String url, final String saveDir, final OnDownloadListener listener) {
        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
                listener.onDownloadFailed();
            }
            @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 = isExistDir(saveDir);
                try {
                    is = response.body().byteStream();
                    long total = response.body().contentLength();
                    File file = new File(savePath, getNameFromUrl(url));
                    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();
                } catch (Exception e) {
                    listener.onDownloadFailed();
                } finally {
                    try {
                        if (is != null)
                            is.close();
                    } catch (IOException e) {
                    }
                    try {
                        if (fos != null)
                            fos.close();
                    } catch (IOException e) {
                    }
                }
            }
        });
    }

    /**
     * @param saveDir
     * @return
     * @throws IOException
     * 判断下载目录是否存在
     */
    private String isExistDir(String saveDir) throws IOException {
        // 下载位置
        File downloadFile = new File(Environment.getExternalStorageDirectory(), saveDir);
        if (!downloadFile.mkdirs()) {
            downloadFile.createNewFile();
        }
        String savePath = downloadFile.getAbsolutePath();
        return savePath;
    }

    /**
     * @param url
     * @return
     * 从下载连接中解析出文件名
     */
    @NonNull
    public static String getNameFromUrl(String url) {
        return url.substring(url.lastIndexOf("/") + 1);
    }

    public interface OnDownloadListener {
        /**
         * 下载成功
         */
        void onDownloadSuccess();

        /**
         * @param progress
         * 下载进度
         */
        void onDownloading(int progress);

        /**
         * 下载失败
         */
        void onDownloadFailed();
    }
}

调用

DownloadUtil.get().download(downloadUrl, "hzh", new DownloadUtil.OnDownloadListener() {
    @Override
    public void onDownloadSuccess() {
        //成功
        Log.i("注意","下载成功");
    }

    @Override
    public void onDownloading(int progress) {
        //进度
        Log.i("注意",progress+"%");
    }

    @Override
    public void onDownloadFailed() {
        //失败
        Log.i("注意","下载失败");
    }
});