Downloading Files from Spring Boot REST APIs

When developing back-end programs, we often need to implement REST APIs so that the front-end (such as Angular, React) can download files. It is easy to implement file downloading REST APIs with Spring Boot StreamingResponseBody.

As the follow code shows, we only need to copy the file’s InputStream to StreamingResponseBody.OutputStream with FileCopyUtils.copy().

import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;

@RestController
@RequestMapping("/logs")
public class LogController {
    @GetMapping(value = "/download", produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    public ResponseEntity<StreamingResponseBody> downloadLog() throws FileNotFoundException {
        InputStream inputStream = new FileInputStream("/path/to/log");
        StreamingResponseBody body = outputStream -> FileCopyUtils.copy(inputStream, outputStream);
        return ResponseEntity.ok()
                .header("Content-Disposition", "attachment;filename=server.log")
                .body(body);
    }
}

Now, you open http://localhost:8080/logs/download with your browser, and the file will be downloaded directly!