Spring服务IdentificationResponse无法转ResponseEntity错误如何解决

错误根因 #

该类转换异常是返回值类型不匹配导致的：

• 你createIdentification方法声明的返回值类型为 ResponseEntity<IdentificationResponse>
• HandleResponse.handleResponse 方法在HTTP状态码为200/201时，返回的是 response.getBody()，也就是IdentificationResponse类型的实例，并非ResponseEntity对象，直接返回就会触发类型转换异常。

额外代码笔误修复 #

你当前代码里存在一处编译错误：
原代码写的HttpEntity<IdentificationRequest> requestHttpEntity = new HttpEntity<>(IdentificationRequest);，构造HttpEntity时误传入了类名，应该改为你已经实例化的对象 identificationRequest，正确写法为：
HttpEntity<IdentificationRequest> requestHttpEntity = new HttpEntity<>(identificationRequest);

两种修复方案 #

你可以根据业务需求二选一：

方案1：保留方法返回ResponseEntity的定义 #

修改handleResponse工具方法，直接返回ResponseEntity对象：

public static <T> ResponseEntity<T> handleResponse(ResponseEntity<T> response) {
    HttpStatus code = response.getStatusCode();
    if (code == HttpStatus.OK || code == HttpStatus.CREATED || code == HttpStatus.NO_CONTENT) {
        return response;
    } else if (code == HttpStatus.BAD_REQUEST) {
        throw new BadRequestException("BadRequest Exception occured while requesting! Exception details: " + response.getBody());
    } else if (code == HttpStatus.UNAUTHORIZED) {
        throw new UnauthorizedException("Unauthorized Exception occured while requesting! Exception details: " + response.getBody());
    } else {
        throw new HttpClientException("Exception occured! Exception details: " + response.getBody(), code.value());
    }
}

修改后原有createIdentification方法的返回逻辑无需调整，类型完全匹配。

方案2：修改业务方法返回值类型 #

如果上层只需要响应体内容，不需要状态码、响应头等信息，可以直接修改createIdentification的返回值类型：

@Override
public IdentificationResponse createIdentification(Request request) {
    IdentificationRequest identificationRequest = new IdentificationRequest(serviceConfig.getIssuerKey(), serviceConfig.getSecureKey());
    identificationRequest.setOperation(ClientConstants.CREATE_IDENTIFICATION_ADD);
    HttpEntity<IdentificationRequest> requestHttpEntity = new HttpEntity<>(identificationRequest);
    ResponseEntity<IdentificationResponse> response = restTemplate.exchange(platform, HttpMethod.POST, requestHttpEntity, IdentificationResponse.class);
    return HandleResponse.handleResponse(response);
}

内容的提问来源于stack exchange，提问作者john deltana