java 参数解析简要过程

1。前端请求到DispatchServlet后，找到相应的handler和adater，之后解析参数，解析参数之前，找到解析参数对应的适配器(spring等提供了20个左右)，之后开始解析

下图的解析是解析一个model对象的适配器解析过程

protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {

		MediaType contentType;
		boolean noContentType = false;
		try {
			contentType = inputMessage.getHeaders().getContentType();
		}
		catch (InvalidMediaTypeException ex) {
			throw new HttpMediaTypeNotSupportedException(ex.getMessage());
		}
		if (contentType == null) {
			noContentType = true;
			contentType = MediaType.APPLICATION_OCTET_STREAM;
		}

		Class<?> contextClass = (parameter != null ? parameter.getContainingClass() : null);
		Class<T> targetClass = (targetType instanceof Class ? (Class<T>) targetType : null);
		if (targetClass == null) {
			ResolvableType resolvableType = (parameter != null ?
					ResolvableType.forMethodParameter(parameter) : ResolvableType.forType(targetType));
			targetClass = (Class<T>) resolvableType.resolve();
		}

		HttpMethod httpMethod = ((HttpRequest) inputMessage).getMethod();
		Object body = NO_VALUE;

		try {
			inputMessage = new EmptyBodyCheckingHttpInputMessage(inputMessage);

			for (HttpMessageConverter<?> converter : this.messageConverters) {
				Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
				if (converter instanceof GenericHttpMessageConverter) {
					GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
					if (genericConverter.canRead(targetType, contextClass, contentType)) {
						if (logger.isDebugEnabled()) {
							logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
						}
						if (inputMessage.getBody() != null) {
							inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
							body = genericConverter.read(targetType, contextClass, inputMessage);
							body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
						}
						else {
							body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
						}
						break;
					}
				}
				else if (targetClass != null) {
					if (converter.canRead(targetClass, contentType)) {
						if (logger.isDebugEnabled()) {
							logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
						}
						if (inputMessage.getBody() != null) {
							inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
							body = ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
							body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
						}
						else {
							body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
						}
						break;
					}
				}
			}
		}
		catch (IOException ex) {
			throw new HttpMessageNotReadableException("Could not read document: " + ex.getMessage(), ex);
		}

		if (body == NO_VALUE) {
			if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||
					(noContentType && inputMessage.getBody() == null)) {
				return null;
			}
			throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
		}

		return body;
	}