Spring Boot REST API return list of files

Question

I am trying to return a list of files from a directory. Here's my code:

package com.demo.web.api.file;

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.demo.core.Logger;

import io.swagger.v3.oas.annotations.Operation;

@RestController
@RequestMapping(value = "/files")
public class FileService {

    private static final Logger logger = Logger.factory(FileService.class);

    @Value("${file-upload-path}")
    public String DIRECTORY;

    @Value("${file-upload-check-subfolders}")
    public boolean CHECK_SUBFOLDERS;

    @GetMapping(value = "/list")
    @Operation(summary = "Get list of Uploaded files")
    public ResponseEntity<List<File>> list() {

        List<File> files = new ArrayList<>();

        if (CHECK_SUBFOLDERS) {

            // Recursive check
            try (Stream<Path> walk = Files.walk(Paths.get(DIRECTORY))) {
                List<Path> result = walk.filter(Files::isRegularFile).collect(Collectors.toList());

                for (Path p : result) {
                    files.add(p.toFile().getAbsoluteFile());
                }
            } catch (Exception e) {

                logger.error(e.getMessage());

            }

        } else {

            // Checks the root directory only.
            try (Stream<Path> walk = Files.walk(Paths.get(DIRECTORY), 1)) {
                List<Path> result = walk.filter(Files::isRegularFile).collect(Collectors.toList());

                for (Path p : result) {
                    files.add(p.toFile().getAbsoluteFile());
                }
            } catch (Exception e) {

                logger.error(e.getMessage());

            }

        }

        return ResponseEntity.ok().body(files);

    }

}

As seen in the code, I am trying to return a list of files.

However, when I test in PostMan, I get a list of string instead.

How can I make it return the file object instead of the file path string? I need to get the file attributes (size, date, etc.) to display in my view.

You can not return the File object, because it is not serializeable. You have to create your own FileDTO and put all the information into it — Jens, Oct 20 '22 at 15:30
BTW: Take care of java naming conventions. variable names should be lower case and camelCase — Jens, Oct 20 '22 at 15:30
I would tend to [this direction](https://stackoverflow.com/q/44342009/592355) ("multipart response") ..but you can also deliver it as JSON (with byte[]s) — xerx593, Oct 20 '22 at 16:19
I needed to rethink this. I don't need to get the actual files, just the size of the file for display. I'll post the solution I came up with. — ericute, Oct 21 '22 at 05:51

score 0 · Answer 1 · answered Oct 20 '22 at 15:38

I would recommend that you change your ResponseEntity<> to return not a List of File but instead, a List of Resource, which you can then use to obtain the file metadata that you need.

public ResponseEntity<List<Resource>> list() {}

You can also try specifying a produces=MediaType... param in your @GetMapping annotation so as to tell the HTTP marshaller which kind of content to expect.

score 0 · Answer 2 · answered Oct 20 '22 at 16:10

You'd have to Create a separate payload with the details you wanna respond with.

    public class FilePayload{
       private String id;
       private String name;
       private String size;

       public static fromFile(File file){
         // create FilePayload from File object here
        }

     }

And convert it using a mapper from your internal DTO objects to payload ones.

final List<FilePayload> payload = files.forEach(FilePayload::fromFile).collect(Collectors.toList());

return new ResponseEntity<>(payload, HttpStatus.OK);

I think you should not return a body in this case as you may be unaware of the size. Better to have another endpoint to GET /files/{id}

ericute · Accepted Answer · 2022-10-25T08:19:56.530

I did give this another thought. What I just needed was the filename, size and date of the file. From there, I can get the file extension and make my list display look good already.

Here's the refactored method:

@GetMapping(value = "/list")
@Operation(summary = "Get list of Uploaded files")
public ResponseEntity<String> list() {

    JSONObject responseObj = new JSONObject();
    List<JSONObject> files = new ArrayList<>();

    // If CHECK_SUBFOLDERS is true, pass MAX_VALUE to make it recursive on all
    // sub-folders. Otherwise, pass 1 to use the root directory only.
    try (Stream<Path> walk = Files.walk(Paths.get(DIRECTORY), CHECK_SUBFOLDERS ? MAX_VALUE : 1)) {
        List<Path> result = walk.filter(Files::isRegularFile).collect(Collectors.toList());
        for (Path p : result) {
            JSONObject file = new JSONObject();
            file.put("name", p.toFile().getName());
            file.put("size", p.toFile().length());
            file.put("lastModified", p.toFile().lastModified());
            files.add(file);
        }
        responseObj.put("data", files);

    } catch (Exception e) {
        String errMsg = CoreUtils.formatString("%s: Error reading files from the directory: \"%s\"",
                e.getClass().getName(), DIRECTORY);
        logger.error(e, errMsg);
        responseObj.put("errors", errMsg);
    }

    return ResponseEntity.ok().body(responseObj.toString());

}

The above was what I ended up doing. I created a JSONObject of the props I need, and then returned the error if it did not succeed. This made it a lot better for me.

Spring Boot REST API return list of files

3 Answers3