记录一个基于okhttp3的一个下载工具类

 implementation 'com.squareup.okhttp3:okhttp:4.12.0'

下面是核心代码

public class DownloadUtil {

    public static final int DOWNLOAD_FAIL = 0;
    public static final int DOWNLOAD_PROGRESS = 1;
    public static final int DOWNLOAD_SUCCESS = 2;
    private static DownloadUtil downloadUtil;
    private final OkHttpClient okHttpClient;

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

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

    /**
     * 下载
     *
     * @param url      下载链接
     * @param saveDir  文件保存目录
     * @param listener 下载监听事件
     */
    public void download(String url, String saveDir, String child, OnDownloadListener listener) {
        this.listener = listener;
        Request request = new Request.Builder().url(url).build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(@NonNull Call call, @NonNull IOException e) {
                Message message = Message.obtain();
                message.what = DOWNLOAD_FAIL;
                mHandler.sendMessage(message);
            }

            @Override
            public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
                InputStream is = null;
                byte[] buf = new byte[2048];
                int len;
                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, child);
                    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
                        Message message = Message.obtain();
                        message.what = DOWNLOAD_PROGRESS;
                        message.obj = progress;
                        mHandler.sendMessage(message);

                    }
                    fos.flush();
                    //下载完成
                    Message message = Message.obtain();
                    message.what = DOWNLOAD_SUCCESS;
                    message.obj = file.getAbsolutePath();
                    mHandler.sendMessage(message);
                } catch (Exception e) {
                    Message message = Message.obtain();
                    message.what = DOWNLOAD_FAIL;
                    mHandler.sendMessage(message);
                } finally {
                    try {
                        if (is != null)
                            is.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    try {
                        if (fos != null) {
                            fos.close();
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
    }

    @NonNull
    private String getNameFromUrl(@NonNull String url) {
        return url.substring(url.lastIndexOf("/") + 1);
    }

    @NonNull
    private String isExistDir(String saveDir) throws IOException {
        final File dir = new File(saveDir);
        if (!dir.exists()) {
            if (!dir.mkdirs()) {
                throw new IOException("mkdir error:" + saveDir);
            }
        }
        return dir.getAbsolutePath();
    }


    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            switch (msg.what) {
                case DOWNLOAD_PROGRESS:
                    listener.onDownloading((Integer) msg.obj);
                    break;
                case DOWNLOAD_FAIL:
                    listener.onDownloadFailed();
                    break;
                case DOWNLOAD_SUCCESS:
                    listener.onDownloadSuccess((String) msg.obj);
                    break;
            }
        }
    };

    OnDownloadListener listener;

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

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

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

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