When working with APIs, there may be a need to send a request with JSON data and receive a response in multipart/form-data format containing a file. In this article, we will discuss how to configure RestTemplate to handle such data. Create a class for serializing JSON to send import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class JsonRequest {
    String field1;
    int field2;
} Configure RestTemplate, prepare, and send a POST request public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        ResponseEntity<byte[]> response = restClient.postForEntity(url, getRequestData(rq, headers), byte[].class);

        return getResource(response.getBody());

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
}

private HttpEntity<String> getRequestData(Object request, HttpHeaders headers) {
    String requestBody;
    try {
        requestBody = new ObjectMapper().writeValueAsString(request);
    } catch (JsonProcessingException e) {
        throw new RuntimeException(e);
    }
    return new HttpEntity<>(removeShielding(requestBody), headers);
}

private Optional<Resource> getResource(byte[] responseBody) throws MessagingException, IOException {
    ByteArrayDataSource dataSource = new ByteArrayDataSource(responseBody, "multipart/form-data");
    MimeMultipart multipart = new MimeMultipart(dataSource);

    int count = multipart.getCount();
    for (int i = 0; i < count; i++) {
        BodyPart bodyPart = multipart.getBodyPart(i);
        String[] contentType = bodyPart.getHeader("Content-Type");

        if ("application/octet-stream".equals(contentType[0])) {
            SharedByteArrayInputStream inputStream = (SharedByteArrayInputStream) bodyPart.getContent();
            final String filename = bodyPart.getFileName();
            Resource resource = new ByteArrayResource(inputStream.readAllBytes()) {
                @Override
                public String getFilename() {
                    return filename;
                }
            };
            return Optional.of(resource);
        }
    }
    return Optional.empty();
} Alternative Approach You can also use a third-party converter MultipartMessageConverter (GitHub Repository). It provides a simple implementation of HttpMessageConverter that can read multipart/form-data and prepare a DTO model, even if a part contains either application/json or application/octet-stream. public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        restClient.getMessageConverters().add(new MultiPartMessageConverter(objectMapper));

        ResponseEntity<ResultModel> responseEntity =
                restClient.postForEntity(url, getRequestData(rq, headers), ResultModel.class);

        final ResultModel resultModel = responseEntity.getBody();
        return Optional.of(resultModel.fileModel.resource);

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
} Conclusion We have reviewed how to use RestTemplate to send a JSON request and receive a response in multipart/form-data format. The approach presented allows for effective handling of multipart responses, which is useful in various scenarios, such as downloading files from a server. An alternative approach using a third-party converter was also presented. You can now use these methods in your applications to work with multipart data, enhancing the functionality and flexibility of your code. When working with APIs , there may be a need to send a request with JSON data and receive a response in multipart/form-data format containing a file. In this article, we will discuss how to configure RestTemplate to handle such data. APIs JSON Create a class for serializing JSON to send import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class JsonRequest {
    String field1;
    int field2;
} import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class JsonRequest {
    String field1;
    int field2;
} Configure RestTemplate, prepare, and send a POST request public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        ResponseEntity<byte[]> response = restClient.postForEntity(url, getRequestData(rq, headers), byte[].class);

        return getResource(response.getBody());

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
}

private HttpEntity<String> getRequestData(Object request, HttpHeaders headers) {
    String requestBody;
    try {
        requestBody = new ObjectMapper().writeValueAsString(request);
    } catch (JsonProcessingException e) {
        throw new RuntimeException(e);
    }
    return new HttpEntity<>(removeShielding(requestBody), headers);
}

private Optional<Resource> getResource(byte[] responseBody) throws MessagingException, IOException {
    ByteArrayDataSource dataSource = new ByteArrayDataSource(responseBody, "multipart/form-data");
    MimeMultipart multipart = new MimeMultipart(dataSource);

    int count = multipart.getCount();
    for (int i = 0; i < count; i++) {
        BodyPart bodyPart = multipart.getBodyPart(i);
        String[] contentType = bodyPart.getHeader("Content-Type");

        if ("application/octet-stream".equals(contentType[0])) {
            SharedByteArrayInputStream inputStream = (SharedByteArrayInputStream) bodyPart.getContent();
            final String filename = bodyPart.getFileName();
            Resource resource = new ByteArrayResource(inputStream.readAllBytes()) {
                @Override
                public String getFilename() {
                    return filename;
                }
            };
            return Optional.of(resource);
        }
    }
    return Optional.empty();
} public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        ResponseEntity<byte[]> response = restClient.postForEntity(url, getRequestData(rq, headers), byte[].class);

        return getResource(response.getBody());

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
}

private HttpEntity<String> getRequestData(Object request, HttpHeaders headers) {
    String requestBody;
    try {
        requestBody = new ObjectMapper().writeValueAsString(request);
    } catch (JsonProcessingException e) {
        throw new RuntimeException(e);
    }
    return new HttpEntity<>(removeShielding(requestBody), headers);
}

private Optional<Resource> getResource(byte[] responseBody) throws MessagingException, IOException {
    ByteArrayDataSource dataSource = new ByteArrayDataSource(responseBody, "multipart/form-data");
    MimeMultipart multipart = new MimeMultipart(dataSource);

    int count = multipart.getCount();
    for (int i = 0; i < count; i++) {
        BodyPart bodyPart = multipart.getBodyPart(i);
        String[] contentType = bodyPart.getHeader("Content-Type");

        if ("application/octet-stream".equals(contentType[0])) {
            SharedByteArrayInputStream inputStream = (SharedByteArrayInputStream) bodyPart.getContent();
            final String filename = bodyPart.getFileName();
            Resource resource = new ByteArrayResource(inputStream.readAllBytes()) {
                @Override
                public String getFilename() {
                    return filename;
                }
            };
            return Optional.of(resource);
        }
    }
    return Optional.empty();
} Alternative Approach You can also use a third-party converter MultipartMessageConverter ( GitHub Repository ). It provides a simple implementation of HttpMessageConverter that can read multipart/form-data and prepare a DTO model, even if a part contains either application/json or application/octet-stream . MultipartMessageConverter GitHub Repository HttpMessageConverter multipart/form-data application/json application/octet-stream public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        restClient.getMessageConverters().add(new MultiPartMessageConverter(objectMapper));

        ResponseEntity<ResultModel> responseEntity =
                restClient.postForEntity(url, getRequestData(rq, headers), ResultModel.class);

        final ResultModel resultModel = responseEntity.getBody();
        return Optional.of(resultModel.fileModel.resource);

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
} public Optional<Resource> postSomeReq(JsonRequest rq) {
    
    String url = "http://somehost/services/retrieve-multipart";

    try {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.setAccept(List.of(MediaType.MULTIPART_FORM_DATA));

        RestTemplate restClient = new RestTemplate();
        restClient.getMessageConverters().add(new MultiPartMessageConverter(objectMapper));

        ResponseEntity<ResultModel> responseEntity =
                restClient.postForEntity(url, getRequestData(rq, headers), ResultModel.class);

        final ResultModel resultModel = responseEntity.getBody();
        return Optional.of(resultModel.fileModel.resource);

    } catch (RestClientException | MessagingException | IOException e) {
        return Optional.empty();
    }
} Conclusion We have reviewed how to use RestTemplate to send a JSON request and receive a response in multipart/form-data format. The approach presented allows for effective handling of multipart responses, which is useful in various scenarios, such as downloading files from a server. An alternative approach using a third-party converter was also presented. multipart/form-data You can now use these methods in your applications to work with multipart data, enhancing the functionality and flexibility of your code.

This story contains AI-generated text. The author has used AI either for research, to generate outlines, or write the text itself. 

Walkthroughs, tutorials, guides, and tips. This story will teach you how to do something new or how to do something better.

How to Receive Files from multipart/form-data Responses Using RestTemplate in Java

About Author

Comments

TOPICS

THIS ARTICLE WAS FEATURED IN

Related Stories

Hierarchical Queries: Comparative Analysis in Oracle and PostgreSQL

What You Need to Know About Advanced Patterns for Symfony HttpClient

Scaling API Integrations in Symfony: Fire-and-Forget, Factories, Auditing & Streams

12 Common Java Mistakes Made by Newcomers

19 Basic Java Interview Questions and Short Sample Answers — 2021

68 Stories To Learn About Java Development

Hierarchical Queries: Comparative Analysis in Oracle and PostgreSQL

What You Need to Know About Advanced Patterns for Symfony HttpClient

Scaling API Integrations in Symfony: Fire-and-Forget, Factories, Auditing & Streams

12 Common Java Mistakes Made by Newcomers

19 Basic Java Interview Questions and Short Sample Answers — 2021

68 Stories To Learn About Java Development

Light-Mode

Classic

Newspaper

Minty

Dark-Mode

Neon Noir

Minty

HN StartUps