How to Prepare a multipart body of a response in Sprint Boot

By Errong Leng - February 24, 2023

Post, Code and Quiet Time.

By Errong Leng – 25 Feb 2023 – View online →

use PartEvent for Reactive Stack

To stream multipart data sequentially, you can provide multipart content through PartEvent objects.

Form fields can be created via FormPartEvent::create.

File uploads can be created via FilePartEvent::create.

You can concatenate the streams returned from methods via Flux::concat, and create a request for the WebClient.

For instance, this sample will POST a multipart form containing a form field and a file.

return Flux.concat(              FormPartEvent.create("field", "field value"),              FilePartEvent.create("file", resource)      );

PS: FormPartEvent are only available since Spring-Web version 6.0.

use MultiValueMap<String, HttpEntity> for Serverlet Stack

MultiValueMap<String, HttpEntity<?>> mixParts = new LinkedMultiValueMap<>();          HttpHeaders jsonHeaders = new HttpHeaders();          jsonHeaders.setContentType(MediaType.APPLICATION_JSON);          try {              mixParts.add("metadata", new HttpEntity<>(objectMapper.writeValueAsString(response), jsonHeaders));          } catch (JsonProcessingException e) {              log.error("Oops!", e);          }          HttpHeaders pdfHeaders = new HttpHeaders();          pdfHeaders.setContentType(MediaType.APPLICATION_PDF);          mixParts.add("pdf", new HttpEntity<>(new ClassPathResource("contract_unsigned.pdf"), pdfHeaders));          return new ResponseEntity<>(mixParts, HttpStatus.OK);