springMVC源碼解析--HandlerMethodArgumentResolverComposite參數解析器集合（二）

上1篇博客springMVC源碼分析--HandlerMethodArgumentResolver參數解析器（1）中我們已介紹了參數解析相干的東西，并且也提到了HandlerMethodArgumentResolverComposite，其簡單來講就是所有的參數解析器的鏈表，保存了springMVC提供的所有的參數解析器，采取職責鏈的模式來完成參數解析器的查找，并完成參數解析生成目標對象。

完全源碼及說明以下：

public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {

	protected final Log logger = LogFactory.getLog(getClass());

	//保存springMVC提供的所有的參數解析器
	private final List<HandlerMethodArgumentResolver> argumentResolvers =
			new LinkedList<HandlerMethodArgumentResolver>();

	//用于緩存已查找過的參數解析器
	private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =
			new ConcurrentHashMap<MethodParameter, HandlerMethodArgumentResolver>(256);
	//獲得所有的參數解析器
	public List<HandlerMethodArgumentResolver> getResolvers() {
		return Collections.unmodifiableList(this.argumentResolvers);
	}

	//判斷參數解析器是不是支持參數解析
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return (getArgumentResolver(parameter) != null);
	}

	//返回參數解析器解析后的數據
	@Override
	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
		if (resolver == null) {
			throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]");
		}
		return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
	}

	//獲得支持某個參數解析的參數解析器
	private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
		HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
		if (result == null) {
			for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
				if (logger.isTraceEnabled()) {
					logger.trace("Testing if argument resolver [" + methodArgumentResolver + "] supports [" +
							parameter.getGenericParameterType() + "]");
				}
				if (methodArgumentResolver.supportsParameter(parameter)) {
					result = methodArgumentResolver;
					this.argumentResolverCache.put(parameter, result);
					break;
				}
			}
		}
		return result;
	}

	//添加參數解析器
	public HandlerMethodArgumentResolverComposite addResolver(HandlerMethodArgumentResolver resolver) {
		this.argumentResolvers.add(resolver);
		return this;
	}
	//獲得參數解析器集合
	public HandlerMethodArgumentResolverComposite addResolvers(List<? extends HandlerMethodArgumentResolver> resolvers) {
		if (resolvers != null) {
			for (HandlerMethodArgumentResolver resolver : resolvers) {
				this.argumentResolvers.add(resolver);
			}
		}
		return this;
	}

}

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