Android项目之文件下载

最新推荐文章于 2022-04-24 09:58:06 发布

原创最新推荐文章于 2022-04-24 09:58:06 发布 · 289 阅读

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本文介绍了一个图片下载任务的实现过程，包括使用同步锁确保线程安全、检查文件是否存在、处理URL有效性、设置HTTP请求参数、读取网络数据并写入本地文件等关键步骤。

public void run() {
        synchronized (cancelLock) {
            if(isCancel) {
                return;
            } else {
                isRunning = true;
            }
        }
        File file = new File(filePath);
        ImageDownloadListener.DownloadResult downloadResult;
        if(file.exists()) {
            downloadResult = ImageDownloadListener.DownloadResult.FILE_EXISTS;
        } else {
            if(url == null || url.trim().equals("")) {
                downloadResult = ImageDownloadListener.DownloadResult.URL_EMPTY;
            } else {
                OutputStream outputStream = null;
                HttpURLConnection httpURLConnection = null;
                try {
                    httpURLConnection = (HttpURLConnection) new URL(url).openConnection();
                    httpURLConnection.setConnectTimeout(5000);
                    httpURLConnection.setReadTimeout(5000);
                    httpURLConnection.setRequestMethod("GET");
                    int responseCode = httpURLConnection.getResponseCode();
                    if(responseCode == 200) {
                        InputStream inputStream = httpURLConnection.getInputStream();

                        synchronized (lock) {
                            file.getParentFile().mkdirs();
                            file.createNewFile();
                        }
                        outputStream = new FileOutputStream(file);

                        byte[] buffer = new byte[1024];
                        int length = -1;
                        int totalSize = httpURLConnection.getContentLength();
                        int currentSize = 0;
                        long lastNotify = System.currentTimeMillis();

                        while ((length = inputStream.read(buffer)) != -1) {
                            outputStream.write(buffer, 0, length);
                            currentSize += length;
                            if((System.currentTimeMillis() - lastNotify) > 200) {
                                new UiTaskProcess(totalSize, currentSize).execute();
                                lastNotify = System.currentTimeMillis();
                            }
                        }//此处有陷阱  如果文件流为空
                        outputStream.flush();
                        new UiTaskProcess(totalSize, currentSize).execute();
                        downloadResult = ImageDownloadListener.DownloadResult.SUCCESSFUL;
                    } else {
                        file.deleteOnExit();
                        downloadResult = ImageDownloadListener.DownloadResult.FAILED;
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                    if(outputStream != null)
                        try {
                            outputStream.flush();
                        } catch (IOException e1) {
                            e1.printStackTrace();
                        }
                    file.delete();
                    downloadResult = ImageDownloadListener.DownloadResult.FAILED;
                } finally {
                    closeQuietly(outputStream);
                    if(httpURLConnection != null)
                        httpURLConnection.disconnect();
                }
            }
            new UiTaskResult(downloadResult).execute();
        }
    }