Spring：ファイルダウンロードでファイル名を設定するのに便利なクラス

package com.example;

import java.nio.charset.StandardCharsets;

import org.springframework.http.ContentDisposition;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;

@Controller
public class SampleController {

  @GetMapping(path = "/download")
  public ResponseEntity<StreamingResponseBody> download(
      @RequestParam(name = "filename") String filename) {

    return ResponseEntity.ok()
        .contentType(MediaType.APPLICATION_OCTET_STREAM)
        .header(
            HttpHeaders.CONTENT_DISPOSITION,
            ContentDisposition.attachment()
                .filename(filename + ".txt", StandardCharsets.UTF_8)
                .build().toString())
        .body(os -> os.write("Hello World!\n".getBytes()));
  }
}