How to post data as csv file to rest entpoint in spring boot using WebClient - spring-boot

Question

I'm trying to migrate data from an in house database to a software. The software has a REST api for this purpose, that expects a csv file.
A working curl call for this API endpoint looks like this:
curl -isk POST -H "customHeaderName:customHeaderValue" -H "Authorization: bearer $TOKEN" -F "data=#accounts.csv" <apiBaseUrl>/gate/account/import/group-accounts
My plan is to post the data directly to the REST endpoint with a spring boot application, without crating a physical csv file first.
My implementation looks like this, with "csvString" beeing a csv formatted String (e.g.: "acc_id,acc_name,acc_desc\r\n1,john.doe,this is john\r\n2,peter.parker,this is peter"):
(I removed this code and added the current version below.)
When I call postAccountsAndGroups(csvString); I get a 415 response indicating that my request Body is not a propper csv file.
EDIT:
It seems like the API endpoint requires a Multipart Form. Therfore I came up with something like this:
import static org.springframework.web.util.UriComponentsBuilder.fromUriString;
import my.package.common.configuration.WebClientConfig;
import java.net.URI;
import java.nio.charset.StandardCharsets;
import lombok.extern.slf4j.Slf4j;
import org.hibernate.service.spi.ServiceException;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.ByteArrayResource;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.client.MultipartBodyBuilder;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
#Service
#Slf4j
public class MyApiImpl implements MyApi {
private final WebClient client;
private final String apiBaseUrl;
public MyApiImpl(
#Qualifier(WebClientConfig.MY_API_CLIENT_CONFIG) WebClient client,
#Value("${external.api.myapi.baseUrl}") String apiBaseUrl) {
this.client = client;
this.apiBaseUrl = apiBaseUrl;
}
#Override
public Mono<HttpStatus> postAccountsAndGroups(String csvString) {
MultipartBodyBuilder builder = new MultipartBodyBuilder();
Resource byteArrayResource = new ByteArrayResource(csvString.getBytes(StandardCharsets.UTF_8));
builder.part("data", byteArrayResource);
return client.post()
.uri(createAccountsUri())
.header("customHeaderName", "customHeaderValue")
.contentType(MediaType.MULTIPART_FORM_DATA)
.body(BodyInserters.fromMultipartData(builder.build()))
.exchangeToMono(response -> {
if (response.statusCode().equals(HttpStatus.OK)) {
return response.bodyToMono(HttpStatus.class).thenReturn(response.statusCode());
} else {
throw new ServiceException("Error uploading file");
}
});
}
private URI createAccountsUri() {
return fromUriString(apiBaseUrl).path("/gate/account/import/group-accounts").build().toUri();
}
}
Now I get 400 Bad Request as response though.

Answer 1

I stil havend found a way to implement my prefered solution. However I came up with this workaround, that relies on persisting the csv file:
In my case I chose "/tmp/account.csv" as file path since my application runs in a docker container with linux os. On a Windows machine you could use something like "C:/myapp/account.csv". The file path is injected vie the application.properties file using the custom value "migration.files.accounts" so it can be configured later.
import static org.springframework.web.util.UriComponentsBuilder.fromUriString;
import my.package.common.configuration.WebClientConfig;
import java.io.File;
import java.io.PrintWriter;
import java.net.URI;
import lombok.extern.slf4j.Slf4j;
import org.hibernate.service.spi.ServiceException;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.FileSystemResource;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.client.MultipartBodyBuilder;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
#Service
#Slf4j
public class PrimedexApiImpl implements PrimedexApi {
private final WebClient client;
private final String apiBaseUrl;
private final FileSystemResource accountsFile;
private final String accountsFilePath;
public PrimedexApiImpl(
#Qualifier(WebClientConfig.MY_API_CLIENT_CONFIG) WebClient client,
#Value("${external.api.api.baseUrl}") String apiBaseUrl,
#Value("${migration.files.accounts}") String accountsFilePath) {
this.client = client;
this.apiBaseUrl = apiBaseUrl;
this.accountsFilePath = accountsFilePath;
this.accountsFile = new FileSystemResource(accountsFilePath);
}
#Override
public Mono<HttpStatus> postAccountsAndGroups(String csvString) {
File csvOutputFile = new File(accountsFilePath);
if (csvOutputFile.delete()) {
log.info("An old version of '{}' was deleted.", accountsFilePath);
}
try (PrintWriter pw = new PrintWriter(csvOutputFile)) {
pw.print(csvString);
} catch (Exception e) {
log.error(e.getMessage(), e);
}
MultipartBodyBuilder builder = new MultipartBodyBuilder();
builder.part("data", accountsFile);
return client.post()
.uri(createAccountsUri())
.header("customHeaderName", "customHeaderValue")
.contentType(MediaType.MULTIPART_FORM_DATA)
.body(BodyInserters.fromMultipartData(builder.build()))
.exchangeToMono(response -> {
if (response.statusCode().equals(HttpStatus.OK)) {
return response.releaseBody().thenReturn(response.statusCode());
} else {
throw new ServiceException("Error uploading file");
}
});
}
private URI createAccountsUri() {
return fromUriString(apiBaseUrl).path("/gate/account/import/group-accounts").build().toUri();
}
}
I used spring-boot-starter-parent version 2.6.3 for this project.