Efficient large-file upload handling in a Spring Boot REST API relies on streaming data instead of buffering it fully in memory, and offloading storage to durable, scalable backends so the application server stays responsive under load.
Key Points: • Stream multipart file content directly to its destination rather than loading the entire file into a byte array. • Process uploads asynchronously, using @Async or a message queue, so the request thread isn't blocked for the full transfer. • Store files outside the application server, such as in Amazon S3 or Azure Blob Storage, rather than on local disk. • Set sensible limits via spring.servlet.multipart.max-file-size and max-request-size to prevent abuse. • Use chunked or multipart upload APIs provided by the cloud storage SDK for very large files.
Example: Instead of reading an uploaded video into memory and then writing it out, the controller streams the InputStream from the MultipartFile directly into an S3 upload call, keeping memory usage flat regardless of file size.
Interview Tip: A concise interview answer is:
"I stream uploaded files directly to durable storage like S3 instead of buffering them in memory, process the upload asynchronously so the request thread isn't tied up, and enforce size limits at the servlet level. That keeps the API responsive and lets storage scale independently of the application servers."