OkHttp 文件下载工具类&文件下载的使用

DownloadUtil

单例模式：主要作用是保证在Java应用程序中，一个类Class只有一个实例存在。 使用Singleton的好处还在于可以节省内存，因为它限制了实例的个数，有利于Java垃圾回收（garbage collection）。

/**
 * Created by wanglingsheng on 2018/5/29.
 * 文件下载工具类（单例模式）
 */

public class DownloadUtil {

    private static DownloadUtil downloadUtil;
    private final OkHttpClient okHttpClient;

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

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


    /**
     * @param url          下载连接
     * @param destFileDir  下载的文件储存目录
     * @param destFileName 下载文件名称
     * @param listener     下载监听
     */

    public void download(final String url, final String destFileDir, final String destFileName, final OnDownloadListener listener) {

        Request request = new Request.Builder()
                .url(url)
                .build();

        OkHttpClient client = new OkHttpClient();

        try {
            Response response = client.newCall(request).execute();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //异步请求
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                // 下载失败监听回调
                listener.onDownloadFailed(e);
            }

            @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
                File dir = new File(destFileDir);
                if (!dir.exists()) {
                    dir.mkdirs();
                }
                File file = new File(dir, destFileName);

                try {

                    is = response.body().byteStream();
                    long total = response.body().contentLength();
                    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);
                        //下载中更新进度条
                        listener.onDownloading(progress);
                    }
                    fos.flush();
                    //下载完成
                    listener.onDownloadSuccess(file);
                } catch (Exception e) {
                    listener.onDownloadFailed(e);
                }finally {

                    try {
                        if (is != null) {
                            is.close();
                        }
                        if (fos != null) {
                            fos.close();
                        }
                    } catch (IOException e) {

                    }

                }


            }
        });
    }


    public interface OnDownloadListener{

        /**
         * 下载成功之后的文件
         */
        void onDownloadSuccess(File file);

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

        /**
         * 下载异常信息
         */

        void onDownloadFailed(Exception e);
    }
}

使用：

/**
     * 文件下载
     */
    private void downFile(String url) {
        DownloadUtil.get().download(url, Environment.getExternalStorageDirectory().getAbsolutePath(), "dtwb2.apk",
                new DownloadUtil.OnDownloadListener() {
                    @Override
                    public void onDownloadSuccess(File file) {
                        if (progressDialog != null && progressDialog.isShowing()) {
                            progressDialog.dismiss();
                        }
                        //下载完成进行相关逻辑操作
                        Message msg = mHandler.obtainMessage();
                        msg.what = 0;
                        mHandler.sendMessage(msg);

                    }

                    @Override
                    public void onDownloading(int progress) {
//                        progressDialog.setProgress(progress);

                        Message msg = mHandler.obtainMessage();
                        msg.what = 11;
                        msg.obj = progress;
                        mHandler.sendMessage(msg);
                    }

                    @Override
                    public void onDownloadFailed(Exception e) {
                        //下载异常进行相关提示操作
                        Message msg = mHandler.obtainMessage();
                        msg.what = 1;
                        msg.obj = e;
                        mHandler.sendMessage(msg);
                    }
                });


    }

progressDialog的配置：

progressDialog = new ProgressDialog(DownloadActivity.this);
                progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                progressDialog.setCancelable(false);
                progressDialog.setCanceledOnTouchOutside(false);
                progressDialog.setTitle("正在下载");
                progressDialog.setMessage("请稍后...");
                progressDialog.setMax(100);
                progressDialog.show();

setProgress的更新用过handler处理message，切换到主线程中更新UI