关于Spring MVC中@ResponseBody怎么知道我需要什么类型

Question

public @ResponseBody searchTreeDicIndustryNode(HttpServletResponse response) {
        List<Person> industries = null;

 @ResponseBody怎么知道我需要什么类型信息呢？

 

希望得到大家帮忙。谢谢。

Answer 1

:D @ResponseBody注解在 method上具体返回什么类型的数据流（json、xml等）主要有两个方面决定的：1. 是否有对应的第三方jar包出现在classpath，比如jackson jar、jaxb2
jar，如果只存在spring mvc就会注册对应的HttpMessageConvert（将return obj写为response的流是靠httpMessageConvert的实现类来完成的） 2. 有@RequestMapping注解的consumes具体的mediaTypes和http请求的accept能结束的mime type来联合决定。 有这两点决定@ResponseBody注解的返回值的返回流的类型具体的实现参见RequestResponseBodyMthodProcessor，java中，具体的写流实现如下在AbstractMessageConverterMethodProcessor.writeWithMessageConverters()来实现的。具体代码：
[code="java"]/**
* Writes the given return type to the given output message.
*
* @param returnValue the value to write to the output message
* @param returnType the type of the value
* @param inputMessage the input messages. Used to inspect the {@code Accept} header.
* @param outputMessage the output message to write to
* @throws IOException thrown in case of I/O errors
* @throws HttpMediaTypeNotAcceptableException thrown when the conditions indicated by {@code Accept} header on
* the request cannot be met by the message converters
*/
@SuppressWarnings("unchecked")
protected void writeWithMessageConverters(T returnValue,
MethodParameter returnType,
ServletServerHttpRequest inputMessage,
ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException {

    Class<?> returnValueClass = returnValue.getClass();

    HttpServletRequest servletRequest = inputMessage.getServletRequest();
    List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(servletRequest);
    List<MediaType> producibleMediaTypes = getProducibleMediaTypes(servletRequest, returnValueClass);

    Set<MediaType> compatibleMediaTypes = new LinkedHashSet<MediaType>();
    for (MediaType r : requestedMediaTypes) {
        for (MediaType p : producibleMediaTypes) {
            if (r.isCompatibleWith(p)) {
                compatibleMediaTypes.add(getMostSpecificMediaType(r, p));
            }
        }
    }
    if (compatibleMediaTypes.isEmpty()) {
        throw new HttpMediaTypeNotAcceptableException(producibleMediaTypes);
    }

    List<MediaType> mediaTypes = new ArrayList<MediaType>(compatibleMediaTypes);
    MediaType.sortBySpecificityAndQuality(mediaTypes);

    MediaType selectedMediaType = null;
    for (MediaType mediaType : mediaTypes) {
        if (mediaType.isConcrete()) {
            selectedMediaType = mediaType;
            break;
        }
        else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
            selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
            break;
        }
    }

    if (selectedMediaType != null) {
        selectedMediaType = selectedMediaType.removeQualityValue();
        for (HttpMessageConverter<?> messageConverter : messageConverters) {
            if (messageConverter.canWrite(returnValueClass, selectedMediaType)) {
                ((HttpMessageConverter<T>) messageConverter).write(returnValue, selectedMediaType, outputMessage);
                if (logger.isDebugEnabled()) {
                    logger.debug("Written [" + returnValue + "] as \"" + selectedMediaType + "\" using [" +
                            messageConverter + "]");
                }
                return;
            }
        }
    }
    throw new HttpMediaTypeNotAcceptableException(allSupportedMediaTypes);
}[/code]