SpringMVC的Body参数拦截

SpringMVC对出参和入参有非常友好的拓展支持,方便你对数据的输入和输出有更大的执行权，我们如何通过SpringMVC定义的结果做一系列处理呢？

入参

RequestBodyAdvice : 针对所有以@RequestBody的参数做处理

参考案例 : JsonViewRequestBodyAdvice

public class JsonViewRequestBodyAdvice extends RequestBodyAdviceAdapter {

    /**
     * 这里是一个前置拦截匹配操作,其实就是告诉你满足为true的才会执行下面的beforeBodyRead方法,这里可以定义自己业务相关的拦截匹配
     * @param methodParameter
     * @param targetType
     * @param converterType
     * @return
     */
    @Override
    public boolean supports(MethodParameter methodParameter, Type targetType,
            Class> converterType) {

        return (AbstractJackson2HttpMessageConverter.class.isAssignableFrom(converterType) &&
                methodParameter.getParameterAnnotation(JsonView.class) != null);
    }

        // 这里就是具体的前置操作了... 下面的例子就是查找这个入参方法是否有@JsonView修饰
    @Override
    public HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter methodParameter,
            Type targetType, Class> 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]);
    }

}

出参

ResponseBodyAdvice: 针对所有以@ResponseBody的参数做处理

参考案例:

@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 就是返回的结果对象,没有处理之前
        return body; 
    }
}

注意事项

自定义的处理对象类上必须得加上@ControllerAdvice注解!
为什么?
源码中RequestMappingHandlerAdapter类在执行initControllerAdviceCache()做初始化的时候会执行一个

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

而ControllerAdviceBean.findAnnotatedBeans方法会查找类上有ControllerAdvice注解的类才会加入到处理当中..

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

所以大家可以根据自己的需要,定义结果的入参和出参结果做一些特殊处理…..