在只知道大华平台地址、用户名、密码、ClientId、ClientSecret情况下下载大华视频监控示例

在只知道大华平台地址、用户名、密码、ClientId、ClientSecret的情况下，可以通过调用大华平台提供的接口获取视频地址，再通过上面提供的Java代码将视频下载到本地。

以下是一个示例代码，可以作为参考：

import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Base64;

public class DownloadVideo {
    public static void main(String[] args) {
        String apiUrl = "http://xxx.xxx.xxx.xxx";
        String username = "your_username";
        String password = "your_password";
        String clientId = "your_client_id";
        String clientSecret = "your_client_secret";
        String cameraIndexCode = "your_camera_index_code"; // 摄像头编号
        String savePath = "D:/video.mp4"; // 保存路径

        try {
            // 获取AccessToken
            String accessToken = getAccessToken(apiUrl, clientId, clientSecret, username, password);

            // 获取视频地址
            String videoUrl = getVideoUrl(apiUrl, accessToken, cameraIndexCode);

            // 下载视频
            URL url = new URL(videoUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5 * 1000);
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Charset", "UTF-8");
            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.setRequestProperty("Authorization", "Bearer " + accessToken);

            InputStream inputStream = conn.getInputStream();
            byte[] getData = readInputStream(inputStream);

            FileOutputStream fos = new FileOutputStream(savePath);
            fos.write(getData);

            if (fos != null) {
                fos.close();
            }
            if (inputStream != null) {
                inputStream.close();
            }

            System.out.println("视频下载完成");

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

    public static String getAccessToken(String apiUrl, String clientId, String clientSecret, String username, String password) throws Exception {
        String authUrl = apiUrl + "/artemis/api/auth/token?appKey=" + clientId + "&appSecret=" + clientSecret;
        URL url = new URL(authUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(5 * 1000);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Charset", "UTF-8");
        conn.setRequestProperty("Content-Type", "application/json");
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setDoOutput(true);
        conn.setDoInput(true);

        String authString = username + ":" + password;
        String authStringEnc = Base64.getEncoder().encodeToString(authString.getBytes("utf-8"));
        conn.setRequestProperty("Authorization", "Basic " + authStringEnc);

        String params = "{\"grantType\":\"password\",\"username\":\"" + username + "\",\"password\":\"" + password + "\"}";
        byte[] postData = params.getBytes("utf-8");
        conn.getOutputStream().write(postData);

        InputStream inputStream = conn.getInputStream();
        byte[] getData = readInputStream(inputStream);
        String result = new String(getData, "utf-8");

        String accessToken = "";
        if (result.contains("accessToken")) {
            String[] arr = result.split(",");
            for (String str : arr) {
                if (str.contains("accessToken")) {
                    accessToken = str.split(":")[1].replaceAll("\"", "");
                    break;
                }
            }
        }

        return accessToken;
    }

    public static String getVideoUrl(String apiUrl, String accessToken, String cameraIndexCode) throws Exception {
        String url = apiUrl + "/artemis/api/video/v1/cameras/" + URLEncoder.encode(cameraIndexCode, "utf-8") + "/previewURLs";
        HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
        conn.setConnectTimeout(5 * 1000);
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Charset", "UTF-8");
        conn.setRequestProperty("Content-Type", "application/json");
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("Authorization", "Bearer " + accessToken);

        InputStream inputStream = conn.getInputStream();
        byte[] getData = readInputStream(inputStream);
        String result = new String(getData, "utf-8");

        String videoUrl = "";
        if (result.contains("url")) {
            String[] arr = result.split(",");
            for (String str : arr) {
                if (str.contains("url")) {
                    videoUrl = str.split(":")[1].replaceAll("\"", "");
                    break;
                }
            }
        }

        return videoUrl;
    }

    public static byte[] readInputStream(InputStream inputStream) throws Exception {
        byte[] buffer = new byte[1024];
        int len;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        while ((len = inputStream.read(buffer)) != -1) {
            bos.write(buffer, 0, len);
        }
        bos.close();
        return bos.toByteArray();
    }
}

上面的代码中，我们首先调用`getAccessToken()`方法获取AccessToken，然后调用`getVideoUrl()`方法获取视频地址，最后通过调用`downloadVideo()`方法将视频下载到本地。需要注意的是，视频地址返回的是一个JSON字符串，需要对字符串进行解析获取实际可用的视频地址。另外，需要将摄像头编号替换成实际可用的编号。