Dropbox Java SDK

2. Reuse client instances

• Singleton DbxClientV2: Instantiate DbxClientV2 once per logical application component (or per user session) and reuse it. Creating many clients wastes resources and increases connection overhead.
• Share HTTP connection pools: Use an HTTP client (OkHttp) with pooled connections to reduce TCP/TLS handshake costs.

3. Prefer chunked (resumable) uploads for large files

• Use upload sessions: For files > 150 MB (or when network reliability is uncertain), use upload session start/append/finish to upload in parts. This enables resuming after failures and parallelism if desired.
• Choose optimal chunk size: Balance between memory and overhead. Common sizes are 4–10 MB; larger chunks reduce API calls but increase memory and re-upload on failure.

Example snippet:

java
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// Start session, append chunks, finish
UploadSessionStartUploader uploader = client.files().uploadSessionStart();
uploader.uploadAndFinish(inputStream, chunkSize);

4. Stream downloads; avoid loading entire files in memory

• Use download builders with streams: Read directly into streams or write to files to avoid OOM for large files.
• Support ranged downloads if applicable: If you need partial data, request ranges to reduce transfer time and memory.

Example:

java
Copy CodeCopied
try (OutputStream out = new FileOutputStream(localFile)) {
    client.files().downloadBuilder(path).download(out);
}

5. Parallelize safely

• Parallelize independent file operations: Use thread pools to process independent uploads/downloads concurrently, but limit concurrency to avoid throttling and resource exhaustion (start with 4–8 threads).
• Avoid concurrent requests for the same file: Coordinate access to prevent race conditions or unnecessary retries.

6. Handle rate limits and retries gracefully

• Respect 429 and 503 responses: Implement exponential backoff with jitter when encountering rate-limiting or transient errors.
• Use Idempotency where possible: For retries, ensure operations are safe to repeat or use upload sessions to avoid duplicate files.

Simple retry pattern:

• On ⁄₅₀₃ or transient network errors: wait random(0..2^n * baseDelay) then retry, up to a limit.

7. Minimize metadata calls

• Batch operations when possible: Use endpoints that allow batch moves/copies if available, and avoid frequent calls to get metadata for many files.
• Cache metadata locally: Cache file lists, cursors, and metadata where appropriate and validate with delta/listFolderLongpoll or listFolderContinue rather than refetching everything.

8. Use cursors for incremental sync

• Use listFolder/listFolderContinue with cursors: For syncing folders, maintain a cursor to receive only changes instead of re-listing entire folders.
• Leverage longpoll: Use listFolderLongpoll to be notified of changes and then fetch updates with listFolderContinue.

9. Secure and efficient authentication

• Reuse access tokens: Persist and reuse OAuth