从 Java 客户端向 FastAPI 服务器发送多部分表单数据时遇到“未找到边界字符”错误

Question

我正在尝试上传文件并将文本参数从 Java 客户端发送到 Python FastAPI 服务器。但是，我遇到了错误：在索引 4 处未找到边界字符 54。

我使用的 CURL 命令运行良好（邮差也）：

curl -X POST \
     -F "files=@/path/to/my/file" \
     -F "param1=someValue" \
     "http://localhost:8000/my_endpoint"

而且我的Python测试也成功了：

with open(input_file, "rb") as file:
    response = client.post(
        url="/my_endpoint",
        data={"param1": "someValue"},
        files=[("files", file)],
    )

但是，我的 Java 实现似乎引起了问题。
FastAPI 服务器日志显示：

Did not find boundary character 121 at index 4
INFO:     127.0.0.1:60803 - "POST /transcribe HTTP/1.1" 400 Bad Request

这是我的Java代码

String boundary = UUID.randomUUID().toString();
HttpRequest httpRequest = HttpRequest.newBuilder()
    .uri(URI.create(myUrl))
    .header("Content-Type", "multipart/form-data; boundary=" + boundary)
    .version(HttpClient.Version.HTTP_1_1)
    .POST(HttpRequest.BodyPublishers.ofByteArray(createFormData(multipartFile)))
    .build();
HttpResponse<String> resp = httpClient.send(httpRequest, HttpResponse.BodyHandlers.ofString());

创建表单数据的方法如下：

private byte[] createFormData(MultipartFile multipartFile) throws IOException {
    HttpEntity httpEntity = createMultipartFile(multipartFile);
    return getByteArray(httpEntity);
}

public HttpEntity createMultipartFile(MultipartFile multipartFile) {
    try {
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();

        byte[] fileBytes = multipartFile.getBytes();
        ByteArrayBody fileBody = new ByteArrayBody(fileBytes, ContentType.DEFAULT_BINARY, multipartFile.getName());
        builder.addPart("files", fileBody);

        builder.addPart("param1", new StringBody("someValue", ContentType.TEXT_PLAIN));

        // Set the multipart entity to the request
        return builder.build();
    } catch (IOException e) {
        throw new MyException(e);
    }
}

public byte[] getByteArray(HttpEntity multipartEntity) {
    try {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        multipartEntity.writeTo(baos);
        return baos.toByteArray();
    } catch (IOException e) {
        throw new MyException(e);
    }
}

有趣的是，当我删除该行时：

.header("Content-Type", "multipart/form-data; boundary=" + boundary)

服务器返回 422 Unprocessable Entity 错误。

如何解决此问题并成功将多部分表单数据从 Java 客户端发送到 FastAPI 服务器？

Answer 1

使用Spring的RestTemplate：

    MultiValueMap<String, Object> body = new LinkedMultiValueMap<>();
    body.add("files", multipartFile.getResource());
    body.add("param1","someValue");
    HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(body, headers);

    ResponseEntity<String> resp = restTemplate.postForEntity(myUrl, requestEntity, String.class);