Why Java File Uploads Crash Servers and How to Stream Them Safely

A technical deep-dive published on DEV Community warns that standard Java tutorials for handling file uploads rely on full in-memory or disk buffering, which can crash production servers when large files arrive. Spring's MultipartFile buffers the entire request body before a controller method is even called, meaning a 2GB upload consumes 2GB of heap or temp disk per concurrent request. The WebFlux alternative using @RequestPart is flagged as equally problematic, as it shifts the buffering rather than eliminating it. The article identifies a specific WebFlux API that enables genuine streaming and outlines the correct approach to use it. This is the first part of a series, with subsequent parts covering S3 storage, file-type detection, and antivirus scanning without loading entire files into memory.