SpringMVC的Body參數攔截

SpringMVC對出參和入參有非常友好的拓展支持,方便你對數據的輸入和輸出有更大的執行權，我們如何通過SpringMVC定義的結果做一系列處理呢？

入參

RequestBodyAdvice : 針對所有以@RequestBody的參數做處理

參考案例 : JsonViewRequestBodyAdvice

public class JsonViewRequestBodyAdvice extends RequestBodyAdviceAdapter {

    /**
     * 這裏是一個前置攔截匹配操作,其實就是告訴你滿足爲true的纔會執行下面的beforeBodyRead方法,這裏可以定義自己業務相關的攔截匹配
     * @param methodParameter
     * @param targetType
     * @param converterType
     * @return
     */
    @Override
    public boolean supports(MethodParameter methodParameter, Type targetType,
            Class<? extends HttpMessageConverter<?>> converterType) {
               
        return (AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType) &&
                methodParameter.getParameterAnnotation(JsonView.class) != null);
    }

        // 這裏就是具體的前置操作了... 下面的例子就是查找這個入參方法是否有@JsonView修飾
    @Override
    public HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter methodParameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> selectedConverterType) throws IOException {

        JsonView annotation = methodParameter.getParameterAnnotation(JsonView.class);
        Class<?>[] classes = annotation.value();
        if (classes.length != 1) {
            throw new IllegalArgumentException(
                    "@JsonView only supported for request body advice with exactly 1 class argument: " + methodParameter);
        }
        return new MappingJacksonInputMessage(inputMessage.getBody(), inputMessage.getHeaders(), classes[0]);
    }

}

出參

ResponseBodyAdvice: 針對所有以@ResponseBody的參數做處理

參考案例:

@ControllerAdvice
public class LogResponseBodyAdvice implements ResponseBodyAdvice {
 
    /**
     *
     * @param returnType
     * @param converterType
     * @return
     */
    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
       // 做任何事情 body 就是返回的結果對象,沒有處理之前
        return body; 
    }
}

注意事項

自定義的處理對象類上必須得加上@ControllerAdvice註解!
爲什麼?
源碼中RequestMappingHandlerAdapter類在執行initControllerAdviceCache()做初始化的時候會執行一個

List<ControllerAdviceBean> beans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
AnnotationAwareOrderComparator.sort(beans);

而ControllerAdviceBean.findAnnotatedBeans方法會查找類上有ControllerAdvice註解的類纔會加入到處理當中..

public static List<ControllerAdviceBean> findAnnotatedBeans(ApplicationContext applicationContext) {
        List<ControllerAdviceBean> beans = new ArrayList<ControllerAdviceBean>();
        for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class)) {
            if (applicationContext.findAnnotationOnBean(name, ControllerAdvice.class) != null) {
                beans.add(new ControllerAdviceBean(name, applicationContext));
            }
        }
        return beans;
    }

所以大家可以根據自己的需要,定義結果的入參和出參結果做一些特殊處理.....