帮我实现一个android 多文件的多线程下载，并且可以断点续传的详细过程

实现多文件的多线程下载需要以下步骤：

1. 创建一个下载任务队列，存放所有需要下载的文件信息，包括文件名、文件大小、下载链接等。

2. 为每个下载任务创建一个下载线程，并将下载任务分配给下载线程。

3. 下载线程使用多线程的方式下载文件，可以根据文件大小划分多个线程，每个线程负责下载文件的一部分数据。

4. 在下载过程中，需要记录已经下载的字节数和下载进度，以便于断点续传。

5. 如果下载过程中出现网络异常或者用户暂停了下载，需要保存已下载的数据，以便于下次继续下载。

6. 如果用户需要暂停或取消下载，需要停止所有下载线程，并删除已下载的数据。

以下是一个简单的多文件多线程下载的示例代码：

1. 创建一个下载任务类，用于存储文件信息和下载状态

public class DownloadTask {
    public String fileName;
    public String url;
    public long fileSize;

    public int status;
    public long progress;
    
    // ...其他属性和方法
}

2. 创建一个下载线程类，用于下载指定的文件

public class DownloadThread extends Thread {
    private String url;
    private long start;
    private long end;
    private RandomAccessFile raf;
    private DownloadListener listener;

    public DownloadThread(String url, long start, long end, RandomAccessFile raf, DownloadListener listener) {
        this.url = url;
        this.start = start;
        this.end = end;
        this.raf = raf;
        this.listener = listener;
    }

    @Override
    public void run() {
        HttpURLConnection conn = null;
        InputStream is = null;
        byte[] buffer = new byte[1024];
        int len;
        try {
            URL url = new URL(this.url);
            conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
            is = conn.getInputStream();
            while ((len = is.read(buffer)) != -1) {
                raf.write(buffer, 0, len);
                listener.onProgress(len);
            }
            listener.onComplete();
        } catch (Exception e) {
            listener.onError(e);
        } finally {
            try {
                if (is != null) {
                    is.close();
                }
                if (conn != null) {
                    conn.disconnect();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

3. 创建一个下载管理类，用于管理所有下载任务和下载线程

public class DownloadManager {
    private static final int MAX_THREAD_COUNT = 3; // 最大下载线程数
    private static final String DOWNLOAD_DIR = "/sdcard/download/"; // 下载文件保存目录

    private List<DownloadTask> taskList;
    private List<DownloadThread> threadList;
    private DownloadListener listener;

    public DownloadManager() {
        taskList = new ArrayList<>();
        threadList = new ArrayList<>();
    }

    // 添加下载任务
    public void addTask(String url, String fileName, long fileSize) {
        DownloadTask task = new DownloadTask();
        task.url = url;
        task.fileName = fileName;
        task.fileSize = fileSize;
        task.status = DownloadTask.STATUS_PENDING;
        taskList.add(task);
        if (listener != null) {
            listener.onTaskAdded(task);
        }
    }

    // 开始下载任务
    public void startTask(DownloadTask task) {
        if (task.status == DownloadTask.STATUS_DOWNLOADING) {
            return;
        }
        task.status = DownloadTask.STATUS_DOWNLOADING;
        File file = new File(DOWNLOAD_DIR + task.fileName);
        long downloadedSize = file.exists() ? file.length() : 0;
        task.progress = downloadedSize;
        long blockSize = (task.fileSize + MAX_THREAD_COUNT - 1) / MAX_THREAD_COUNT;
        for (int i = 0; i < MAX_THREAD_COUNT; i++) {
            long start = i * blockSize + downloadedSize;
            long end = (i == MAX_THREAD_COUNT - 1) ? task.fileSize - 1 : (i + 1) * blockSize - 1;
            try {
                RandomAccessFile raf = new RandomAccessFile(file, "rw");
                raf.seek(start);
                DownloadThread thread = new DownloadThread(task.url, start, end, raf, new DownloadListener() {
                    @Override
                    public void onProgress(int len) {
                        synchronized (task) {
                            task.progress += len;
                            if (listener != null) {
                                listener.onProgress(task);
                            }
                        }
                    }

                    @Override
                    public void onComplete() {
                        synchronized (task) {
                            boolean allThreadsComplete = true;
                            for (DownloadThread thread : threadList) {
                                if (thread.getState() != State.TERMINATED) {
                                    allThreadsComplete = false;
                                    break;
                                }
                            }
                            if (allThreadsComplete) {
                                task.status = DownloadTask.STATUS_COMPLETE;
                                if (listener != null) {
                                    listener.onComplete(task);
                                }
                            }
                        }
                    }

                    @Override
                    public void onError(Exception e) {
                        synchronized (task) {
                            task.status = DownloadTask.STATUS_ERROR;
                            if (listener != null) {
                                listener.onError(task, e);
                            }
                        }
                    }
                });
                threadList.add(thread);
                thread.start();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 暂停下载任务
    public void pauseTask(DownloadTask task) {
        task.status = DownloadTask.STATUS_PAUSED;
        for (DownloadThread thread : threadList) {
            thread.interrupt();
        }
        threadList.clear();
        if (listener != null) {
            listener.onPause(task);
        }
    }

    // 取消下载任务
    public void cancelTask(DownloadTask task) {
        task.status = DownloadTask.STATUS_CANCELED;
        File file = new File(DOWNLOAD_DIR + task.fileName);
        if (file.exists()) {
            file.delete();
        }
        for (DownloadThread thread : threadList) {
            thread.interrupt();
        }
        threadList.clear();
        if (listener != null) {
            listener.onCancel(task);
        }
    }

    // 设置下载监听器
    public void setDownloadListener(DownloadListener listener) {
        this.listener = listener;
    }

    public interface DownloadListener {
        void onTaskAdded(DownloadTask task);

        void onProgress(DownloadTask task);

        void onComplete(DownloadTask task);

        void onPause(DownloadTask task);

        void onCancel(DownloadTask task);

        void onError(DownloadTask task, Exception e);
    }
}

4. 在Activity中调用下载管理类，实现文件下载功能

public class DownloadActivity extends AppCompatActivity implements DownloadManager.DownloadListener {
    private DownloadManager downloadManager;
    private ListView listView;
    private DownloadListAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download);

        downloadManager = new DownloadManager();
        downloadManager.setDownloadListener(this);

        listView = (ListView) findViewById(R.id.list_view);
        adapter = new DownloadListAdapter(this, downloadManager.getTaskList());
        listView.setAdapter(adapter);
    }

    // 添加新的下载任务
    public void addTask(String url, String fileName, long fileSize) {
        downloadManager.addTask(url, fileName, fileSize);
    }

    // 开始下载任务
    public void startTask(DownloadTask task) {
        downloadManager.startTask(task);
    }

    // 暂停下载任务
    public void pauseTask(DownloadTask task) {
        downloadManager.pauseTask(task);
    }

    // 取消下载任务
    public void cancelTask(DownloadTask task) {
        downloadManager.cancelTask(task);
    }

    @Override
    public void onTaskAdded(DownloadTask task) {
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onProgress(DownloadTask task) {
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onComplete(DownloadTask task) {
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onPause(DownloadTask task) {
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onCancel(DownloadTask task) {
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onError(DownloadTask task, Exception e) {
        adapter.notifyDataSetChanged();
    }
}

以上代码仅作为示例，实际项目中还需要考虑一些异常情况，例如网络异常、存储空间不足等。同时应该注意线程同步和异常处理，以确保下载任务的正确性和稳定性。