Android实现多线程下载安装

Android 实现多线程下载安装主要需要以下步骤：

1. 获取下载链接和文件名：在下载之前，需要先获取下载链接和文件名。

2. 创建多个线程：每个线程负责下载文件的一部分。这里可以使用 Java 的线程池技术，通过线程池管理多个线程。

3. 下载文件：每个线程下载文件的一部分，并将下载的数据写入本地文件。

4. 合并文件：所有线程下载完成后，将下载的文件片段合并为完整的文件。

5. 安装应用：下载完成后，通过系统的 Intent 启动安装程序，将下载的应用安装到设备上。

下面是一个简单的示例代码：

public class DownloadTask {
    private static final int THREAD_COUNT = 3; // 线程数量
    private String downloadUrl; // 下载链接
    private String fileName; // 文件名
    private String savePath; // 保存路径
    private long fileSize; // 文件大小
    private Context context;

    public DownloadTask(Context context, String downloadUrl, String fileName, String savePath) {
        this.context = context;
        this.downloadUrl = downloadUrl;
        this.fileName = fileName;
        this.savePath = savePath;
    }

    public void startDownload() {
        try {
            URL url = new URL(downloadUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(5000);
            fileSize = connection.getContentLength();
            connection.disconnect();

            RandomAccessFile file = new RandomAccessFile(savePath + fileName, "rw");
            file.setLength(fileSize);
            file.close();

            ExecutorService executor = Executors.newFixedThreadPool(THREAD_COUNT);
            long blockSize = fileSize / THREAD_COUNT;
            for (int i = 0; i < THREAD_COUNT; i++) {
                long start = i * blockSize;
                long end = (i + 1) * blockSize - 1;
                if (i == THREAD_COUNT - 1) {
                    end = fileSize - 1;
                }
                DownloadThread thread = new DownloadThread(context, downloadUrl, savePath, fileName, start, end);
                executor.execute(thread);
            }
            executor.shutdown();
            while (!executor.isTerminated()) {
                Thread.sleep(100);
            }
            mergeFile();

            installApk();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 合并文件
    private void mergeFile() throws IOException {
        File file = new File(savePath + fileName);
        FileOutputStream fos = new FileOutputStream(file);
        for (int i = 0; i < THREAD_COUNT; i++) {
            FileInputStream fis = new FileInputStream(savePath + fileName + ".part" + i);
            byte[] buffer = new byte[1024];
            int len;
            while ((len = fis.read(buffer)) != -1) {
                fos.write(buffer, 0, len);
            }
            fis.close();
            new File(savePath + fileName + ".part" + i).delete();
        }
        fos.close();
    }

    // 安装应用
    private void installApk() {
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(Uri.fromFile(new File(savePath + fileName)), "application/vnd.android.package-archive");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(intent);
    }
}

class DownloadThread extends Thread {
    private static final int BUFFER_SIZE = 1024;
    private Context context;
    private String downloadUrl;
    private String savePath;
    private String fileName;
    private long start;
    private long end;

    public DownloadThread(Context context, String downloadUrl, String savePath, String fileName, long start, long end) {
        this.context = context;
        this.downloadUrl = downloadUrl;
        this.savePath = savePath;
        this.fileName = fileName;
        this.start = start;
        this.end = end;
    }

    @Override
    public void run() {
        try {
            URL url = new URL(downloadUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(5000);
            connection.setRequestProperty("Range", "bytes=" + start + "-" + end);

            File file = new File(savePath + fileName + ".part" + getId());
            FileOutputStream fos = new FileOutputStream(file);
            InputStream is = connection.getInputStream();
            byte[] buffer = new byte[BUFFER_SIZE];
            int len;
            while ((len = is.read(buffer)) != -1) {
                fos.write(buffer, 0, len);
            }
            fos.close();
            is.close();
            connection.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

在这个示例中，我们创建了一个 `DownloadTask` 类来管理下载任务。`startDownload()` 方法启动下载任务，首先获取文件大小，并创建一个与文件大小相同的空文件。然后使用线程池创建多个线程来下载文件的不同部分。每个线程下载完成后，将文件片段写入以该线程 ID 命名的临时文件中。所有线程结束后，将临时文件合并为完整的文件，并启动安装程序来安装应用。