Android代码实现文件下载

Android代码对于文件的下载网上有很多的版本，但是有一些版本是不对的，总是报错。于是在这里，给大家整理了一个文件下载的工具类，代码如下:
下面展示一些 内联代码片。

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();
    }
 
    /**
     * url 下载连接
     * saveDir 储存下载文件的SDCard目录
     * listener 下载监听
     */
    public void download( 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) {
                    }
                }
            }
        });
    }
 
    /**
     *  saveDir
     * 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;
    }
 
    /**
     *  url
     * 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();
    }
}

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