Providing users with the ability to download files—whether they are generated PDFs, exported Excel sheets, or simple text files—is a core requirement for most web applications. In the Java ecosystem, achieving this involves more than just reading bytes; it requires a proper understanding of HTTP headers and the underlying web framework.
: If your filenames contain special characters or non-ASCII symbols, you must encode them (e.g., filename*=UTF-8''filename.ext ) to prevent browser errors. java code to download file in browser
: Always use buffered streams (like BufferedInputStream ) when dealing with large files to improve performance. Providing users with the ability to download files—whether
import org.springframework.core.io.FileSystemResource; import org.springframework.core.io.Resource; import org.springframework.http.HttpHeaders; import org.springframework.http.MediaType; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import java.io.File; @RestController public class DownloadController { @GetMapping("/api/download") public ResponseEntity downloadFile() { File file = new File("reports/data_export.csv"); Resource resource = new FileSystemResource(file); return ResponseEntity.ok() .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getName() + "\"") .contentLength(file.length()) .contentType(MediaType.APPLICATION_OCTET_STREAM) .body(resource); } } Use code with caution. Why use ResponseEntity ? : Always use buffered streams (like BufferedInputStream )
: Never pass a raw file path from the user's browser directly to your file system logic. This prevents Path Traversal attacks where users could download sensitive system files.
: Defines the MIME type (e.g., application/pdf , image/png , or application/octet-stream for generic binary data).