Play Framework会话注入对象及AWS查询已传输字节方法咨询

Hey there! Let's tackle your two questions step by step—they're both super relevant for tracking upload progress with AWS and Play Framework:

First off, a quick heads-up: Play's built-in Session is cookie-based and only supports storing string values (plus it has size limits), so you can't directly stuff the AWS Upload object into it. Instead, use a server-side storage layer to track the upload, then reference it via a unique ID in the session. Here's how to do it:

• Create a server-side state store: Use Play's built-in Cache (great for single instances) or a distributed cache like Redis (if you're running multiple Play instances). This is where you'll keep the AWS Upload object tied to a unique ID.
• Generate a unique upload identifier: When starting the upload, create a UUID (or similar unique string) to act as your uploadId. Associate this ID with the AWS Upload object and store it in your cache with a reasonable expiration time (longer than your expected maximum upload duration).
• Pass the ID to the session: Store the uploadId in Play's Session (since it's a string, this works perfectly). Alternatively, return it to the frontend and let them store it in localStorage—either way works.
• Build an AJAX status endpoint: Create a Play controller endpoint (e.g., GET /upload/status/:uploadId) that fetches the Upload object from the cache using the ID. Call upload.getProgress().getBytesTransferred() to get the current bytes transferred, then return that data (plus a isDone flag) as JSON to the frontend.
• Clean up after completion: Once the upload finishes (success or failure), remove the Upload object from the cache to avoid memory leaks.

Quick Code Example (Java) #

Initializing the upload and storing the ID:

public Result startUpload() {
    // Initialize your AWS TransferManager and Upload object
    Upload upload = transferManager.upload("my-bucket", "my-file-key", new File("/path/to/file"));
    
    // Generate unique ID and store upload in cache (1-hour expiration)
    String uploadId = UUID.randomUUID().toString();
    Cache.set(uploadId, upload, 3600);
    
    // Store ID in Play Session
    session("currentUploadId", uploadId);
    
    // Return ID to frontend (optional, if using localStorage instead)
    return ok(Json.toJson(uploadId));
}

Fetching upload status via AJAX endpoint:

public Result getUploadStatus(String uploadId) {
    Upload upload = Cache.getOrElse(uploadId, () -> null);
    
    if (upload == null) {
        return notFound(Json.toJson("Upload not found or expired"));
    }
    
    long bytesTransferred = upload.getProgress().getBytesTransferred();
    boolean isComplete = upload.isDone();
    
    return ok(Json.toJson(Map.of(
        "bytesTransferred", bytesTransferred,
        "isComplete", isComplete
    )));
}

Absolutely! If you're using S3 (the most common AWS service for file uploads), you can easily retrieve the final size of the uploaded object using its unique key (or object ID). Here's what you need to know:

• For standard uploads: Once the upload completes successfully, the object's Content-Length metadata (retrieved via the HeadObject API) will give you the total bytes transferred. This is the definitive size of the object stored in S3.
• For multipart uploads: If you used S3's multipart upload feature, you can use the ListParts API to sum up the sizes of all completed parts before finalizing the upload. After finalization, HeadObject will still give you the total size.
• Access requirements: You'll need AWS credentials with permissions to call HeadObject (or ListParts for multipart) on the target bucket and object.

Quick Code Example (AWS SDK 2.x - Java) #

public long getUploadedFileSize(String bucketName, String objectKey) {
    try (S3Client s3Client = S3Client.create()) {
        HeadObjectRequest request = HeadObjectRequest.builder()
            .bucket(bucketName)
            .key(objectKey)
            .build();
        
        HeadObjectResponse response = s3Client.headObject(request);
        return response.contentLength();
    } catch (S3Exception e) {
        // Handle errors (e.g., object not found, permissions issues)
        throw new RuntimeException("Failed to retrieve object size: " + e.getMessage());
    }
}

Keep in mind: This returns the final size of the object. If the upload failed partway, the object either won't exist (for standard uploads) or you'll need to use ListMultipartUploads to find incomplete uploads and check their parts.

内容的提问来源于stack exchange，提问作者Smart Developer