缘起
有一个需求，在进入controller之前验证调用次数是否超过限制，在响应之后判断是否正常返回，对调用次数进行+1，发现带@RestController的类和带@ResponseBody的方法在被调用后response会直接写入输出流，在postHandle和afterCompletion这两个方法执行之前就已经把数据返回，导致这两个方法里面的response根本获取不到响应数据(也无法拿到头信息等)。

解决方案
先解释一下为什么不用过滤器，因为这个需求是拦截带某个特定注解的controller方法，还需要获取到这个注解里面的一些数据，因此Filter方案没法满足这样的需求。怎么解决这个问题呢？那就是使用@ControllerAdvice，这个注解标注的类需要实现ResponseBodyAdvice，这样在response返回前会调用这个类的beforeBodyWrite方法，我们就在beforeBodyWrite方法里面做文章，来进行“曲线救国”。代码：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import java.lang.reflect.Method;

/**
 **/
@ControllerAdvice
public class ApiResponseBody implements ResponseBodyAdvice<RestResult> {

    private static final Logger logger = LoggerFactory.getLogger(ApiResponseBody.class);
    @Autowired
    private RedisClientWrapper redisClientWrapper;

    @Override
    public boolean supports(MethodParameter methodParameter, Class<? extends HttpMessageConverter<?>> aClass) {

        Method method = methodParameter.getMethod();
        return method.isAnnotationPresent(InvokeLimit.class);
    }

    @Override
    public RestResult beforeBodyWrite(RestResult restResult, MethodParameter methodParameter, MediaType mediaType, Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
        logger.info("调用限制拦截器进入次数增加");
        if(ResultEnums.SUCCESS.getCode().equals(restResult.getCode())){
            String appId =  methodParameter.getMethod().getAnnotation(InvokeLimit.class).value();
            String cusNo = serverHttpRequest.getHeaders().get(BussConstant.INVOKE_HEADER_CUS_NO).get(0);
            String times = redisClientWrapper.increment(appId + ":" + BussConstant.INVOKE_NUM_CURRENT_PREFIX + cusNo);
            logger.info("调用限制拦截器次数增加完成，cusNo={}，appId={}，当前次数为：{}",cusNo,appId,times);
        }

        return restResult;
    }
}

supports方法是来给定条件判断是否该调用beforeBodyWrite，MethodParameter里面有各种数据，其中就有我想要的：调用了哪个方法，从而获得标注在上面的注解。beforeBodyWrite中就是我的逻辑，其中也包含MethodParameter，并且还有封装了的request和response，非常灵活。
关键代码：@seeorg.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor#writeWithMessageConverterswriteWithMessageConverters(@Nullable T value, MethodParameter returnType,ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)

if (selectedMediaType != null) {
	selectedMediaType = selectedMediaType.removeQualityValue();
	for (HttpMessageConverter<?> converter : this.messageConverters) {
		GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
				(GenericHttpMessageConverter<?>) converter : null);
		if (genericConverter != null ?
				((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
				converter.canWrite(valueType, selectedMediaType)) {
                        //关键代码      
			body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
					(Class<? extends HttpMessageConverter<?>>) converter.getClass(),
					inputMessage, outputMessage);
			if (body != null) {
				Object theBody = body;
				LogFormatUtils.traceDebug(logger, traceOn ->
						"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
				addContentDispositionHeader(inputMessage, outputMessage);
				if (genericConverter != null) {
					genericConverter.write(body, targetType, selectedMediaType, outputMessage);
				}
				else {
					((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
				}
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Nothing to write: null body");
				}
			}
			return;
		}
	}
}                   

注：同理还有RequestBodyAdvice-> @RequestBody等