使用前先依賴 Okhttp：

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

直接復(fù)制代碼：

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 下載連接
     * @param saveDir 儲存下載文件的SDCard目錄
     * @param listener 下載監(jiān)聽
     */
    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) {
                // 下載失敗
                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;
                // 儲存下載文件的目錄
                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);
                        // 下載中
                        listener.onDownloading(progress);
                    }
                    fos.flush();
                    // 下載完成
                    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
     * 判斷下載目錄是否存在
     */
    private String isExistDir(String saveDir) throws IOException {
        // 下載位置
        File downloadFile = new File(Environment.getExternalStorageDirectory(), saveDir);
        if (!downloadFile.mkdirs()) {
            downloadFile.createNewFile();
        }
        String savePath = downloadFile.getAbsolutePath();
        return savePath;
    }

    /**
     * @param url
     * @return
     * 從下載連接中解析出文件名
     */
    @NonNull
    private String getNameFromUrl(String url) {
        return url.substring(url.lastIndexOf("/") + 1);
    }

    public interface OnDownloadListener {
        /**
         * 下載成功
         */
        void onDownloadSuccess();

        /**
         * @param progress
         * 下載進(jìn)度
         */
        void onDownloading(int progress);

        /**
         * 下載失敗
         */
        void onDownloadFailed();
    }
}

使用：

DownloadUtil.get().download(url, "download", new DownloadUtil.OnDownloadListener() {
    @Override
    public void onDownloadSuccess() {
        Utils.showToast(MainActivity.this, "下載完成");
    }
    @Override
    public void onDownloading(int progress) {
        progressBar.setProgress(progress);
    }
    @Override
    public void onDownloadFailed() {
        Utils.showToast(MainActivity.this, "下載失敗");
    }
});