Spring Boot中ResponseBodyAdvice的beforeBodyWrite无法获取响应状态与头信息

为什么原代码无法获取响应状态码和头？ #

ResponseBodyAdvice.beforeBodyWrite方法的执行时机是HTTP消息转换器写入响应体之前，此时Spring MVC尚未将最终的响应状态码、响应头写入到ServletResponse中（这些元数据通常在后续请求处理阶段，比如异常处理、响应提交前才会被设置），所以你强转后获取到的是ServletResponse的初始状态，自然无法拿到实际的响应信息。

解决方案 #

方案1：使用HandlerInterceptor的afterCompletion方法 #

该方法在整个请求处理完成（响应已完全准备好，即将发送给客户端）后执行，此时可以可靠获取所有响应元数据。

第一步：实现HandlerInterceptor

@Component
@Slf4j
public class ResponseLogInterceptor implements HandlerInterceptor {

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // 获取响应状态码
        int statusCode = response.getStatus();
        // 整理响应头为Map格式，方便日志输出
        Map<String, String> responseHeaders = new HashMap<>();
        response.getHeaderNames().forEach(headerName -> 
            responseHeaders.put(headerName, response.getHeader(headerName))
        );

        log.info("response code is {}", statusCode);
        log.info("response headers are {}", responseHeaders);
    }
}

第二步：注册拦截器

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    private final ResponseLogInterceptor responseLogInterceptor;

    public WebMvcConfig(ResponseLogInterceptor responseLogInterceptor) {
        this.responseLogInterceptor = responseLogInterceptor;
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(responseLogInterceptor)
                .addPathPatterns("/**"); // 匹配所有需要日志的请求路径
    }
}

方案2：同时记录响应体、状态码和头（推荐） #

如果需要同时记录响应体，可结合ContentCachingResponseWrapper包装响应，缓存响应内容后在afterCompletion中统一获取所有信息：

@Component
@Slf4j
public class CompleteResponseLogInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 用ContentCachingResponseWrapper包装原始响应，缓存响应内容
        if (!(response instanceof ContentCachingResponseWrapper)) {
            response = new ContentCachingResponseWrapper(response);
        }
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        ContentCachingResponseWrapper cachedResponse = (ContentCachingResponseWrapper) response;

        // 获取响应状态码
        int statusCode = cachedResponse.getStatus();
        // 整理响应头
        Map<String, String> responseHeaders = new HashMap<>();
        cachedResponse.getHeaderNames().forEach(headerName -> 
            responseHeaders.put(headerName, cachedResponse.getHeader(headerName))
        );
        // 获取响应体（注意编码格式，避免乱码）
        String responseBody = new String(cachedResponse.getContentAsByteArray(), cachedResponse.getCharacterEncoding());

        log.info("response code is {}", statusCode);
        log.info("response headers are {}", responseHeaders);
        log.info("response body is {}", responseBody);

        // 必须将缓存的响应内容写出到原始响应，否则客户端无法收到响应
        cachedResponse.copyBodyToResponse();
    }
}

同样需要在WebMvcConfig中注册这个拦截器。

内容的提问来源于stack exchange，提问作者Albin