How can you implement file upload and download functionality in a Spring Boot application?

Implementing File Upload

Implementing file upload functionality in Spring Boot typically involves using the MultipartFile interface from Spring MVC. The following steps and example code will guide you through the implementation:

1. Dependency Addition: Add the Spring Boot Web dependency to your pom.xml.

xml
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

1. Controller Implementation: Create a controller to handle HTTP requests for file uploads.

java
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

@RestController
public class FileUploadController {

    @PostMapping("/upload")
    public String handleFileUpload(@RequestParam("file") MultipartFile file) {
        try {
            String fileName = file.getOriginalFilename();
            // File saving logic
            file.transferTo(new File("path/to/destination/" + fileName));
            return "File uploaded successfully";
        } catch (Exception e) {
            return "File upload failed: " + e.getMessage();
        }
    }
}

1. Configuring File Size Limits: Set the maximum file size and request size in application.properties or application.yml.

properties
# application.properties
spring.servlet.multipart.max-file-size=2MB
spring.servlet.multipart.max-request-size=2MB

Implementing File Download

File download functionality can be implemented by having a controller return a Resource:

1. Controller Implementation: Create a controller to handle HTTP requests for file downloads.

java
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import java.nio.file.Path;
import java.nio.file.Paths;

@RestController
public class FileDownloadController {

    @GetMapping("/download")
    public ResponseEntity<Resource> downloadFile(@RequestParam String filename) {
        try {
            Path file = Paths.get("path/to/destination").resolve(filename);
            Resource resource = new UrlResource(file.toUri());

            if (resource.exists() || resource.isReadable()) {
                return ResponseEntity.ok()
                        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + resource.getFilename() + "")
                        .body(resource);
            } else {
                throw new RuntimeException("File is not accessible");
            }
        } catch (Exception e) {
            throw new RuntimeException("Error: " + e.getMessage());
        }
    }
}

1. Exception Handling: Handle cases where the file does not exist or is unreadable to provide users with appropriate feedback.

The above provides the basic steps and example code for implementing file upload and download functionality in a Spring Boot application. These features should be adjusted and optimized according to specific business requirements, such as adding security checks (to prevent malicious file uploads) and using a database to manage file metadata.