File Upload and Download in Spring Boot provides mechanisms to receive, store, manage, and transmit binary data (such as documents, images, videos, and PDFs) over HTTP. Built on top of Spring MVC’s multipart resolver support, it enables applications to seamlessly process inbound file data from web or mobile clients and stream files back for download or preview.
1. Single File Upload
Single file upload handles receiving a single binary file transmitted via an HTTP
POST request using multipart/form-data encoding.-
MultipartFileInterface: Spring encapsulates the uploaded file inside aMultipartFileobject injected into a controller method via@RequestParam("file") MultipartFile file. -
Operations: Provides convenient methods to inspect file metadata (
getOriginalFilename(),getContentType(),getSize()) and transfer bytes to persistent targets (file.transferTo(destinationPath)or reading theInputStream). -
Validation & Limits: Developers often validate the file’s extension, MIME type, and size to enforce security constraints before saving it to a local filesystem, cloud storage (such as AWS S3 or Google Cloud Storage), or a database blob.
2. Multiple File Upload
Multiple file upload allows users to upload a batch of files in a single HTTP request.
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Collection Handling: Captured in controller methods by accepting an array or collection of multipart files, such as
@RequestParam("files") MultipartFile[] filesorList<MultipartFile> files. -
Iterative Processing: The application loops through the collection to validate and save each file individually, handling partial successes, aggregate file size restrictions, and bulk database record creation.
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Configuration: File size thresholds for both individual files and the total request payload are configured in
application.properties(e.g.,spring.servlet.multipart.max-file-sizeandspring.servlet.multipart.max-request-size).
3. File Download
File download retrieves a stored file from disk, storage, or memory and streams its byte stream back to the client.
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Resource Wrappers: Uses Spring’s
Resourceabstractions—such asUrlResource,FileSystemResource, orByteArrayResource—to stream the file contents efficiently without loading large files entirely into RAM. -
HTTP Headers: Returns a
ResponseEntity<Resource>configured with:
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HttpHeaders.CONTENT_DISPOSITION: Defines whether the file should be downloaded as an attachment (e.g.,attachment; filename="data.csv") or displayed inline in the browser (e.g.,inline). -
HttpHeaders.CONTENT_TYPE: Specifies the media type (e.g.,MediaType.APPLICATION_PDF,MediaType.IMAGE_JPEG, orMediaType.APPLICATION_OCTET_STREAM). -
HttpHeaders.CONTENT_LENGTH: Indicates the file size so clients can display transfer progress.
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