本文章主要介绍HandlerMethodArgumentResolver在SpringMVC中的使用，介绍几个HandlerMethodArgumentResolver具体的使用情况，然后说明HandlerMethodArgumentResolver的注册来源以及如何自定义注册。

首先具体看下请求映射到的handler的对应的映射函数的参数形式有哪些：

HandlerMethodArgumentResolver接口只有两个方法：

//判断是否支持要转换的参数类型boolean supportsParameter(MethodParameter parameter);//当支持后进行相应的转换Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;

HandlerMethodArgumentResolver接口的抽象类：AbstractMessageConverterMethodArgumentResolver仅仅引入了HttpMessageConverter，即转换的工作有这些HttpMessageConverter来完成具体的转换和判断由子类来实现。

如下：

public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {	protected final Log logger = LogFactory.getLog(getClass());	protected final List
    
     > messageConverters;	protected final List
     
       allSupportedMediaTypes;     //略}
     
    

AbstractMessageConverterMethodArgumentResolver 的抽象子类AbstractMessageConverterMethodProcessor仅仅是加入了对响应数据进行转换的支持。

也就是AbstractMessageConverterMethodProcessor的子类不仅可以用来转换请求数据，也可以用来转换响应数据。

AbstractMessageConverterMethodProcessor的子类HttpEntityMethodProcessor，支持请求和响应的转换，代码如下：

@Override	public boolean supportsParameter(MethodParameter parameter) {		return HttpEntity.class.equals(parameter.getParameterType());	}	@Override	public boolean supportsReturnType(MethodParameter returnType) {		return HttpEntity.class.isAssignableFrom(returnType.getParameterType());	}

使用场景如下：

@RequestMapping(value="/test/http",method=RequestMethod.POST)	@ResponseBody	public Map
    
      testHttp(HttpEntity
     
       httpEntity)             //略         }@RequestMapping(value="/test/httpEntity",method=RequestMethod.GET)	public HttpEntity
      
        testHttpEntity(){		//略	}
      
     
    

AbstractMessageConverterMethodProcessor的子类RequestResponseBodyMethodProcessor：支持@RequestBody和@ResponseBody,代码如下：

@Override	public boolean supportsParameter(MethodParameter parameter) {               //查找参数中是否含有@RequestBody注解		return parameter.hasParameterAnnotation(RequestBody.class);	}	@Override	public boolean supportsReturnType(MethodParameter returnType) {//查找参数中是否含有@RequestBody注解或者controller类上是否含有@RequestBody		return ((AnnotationUtils.findAnnotation(returnType.getContainingClass(), ResponseBody.class) != null) ||				(returnType.getMethodAnnotation(ResponseBody.class) != null));	}

使用场景如下：

@RequestMapping(value="/test/requestBody",method=RequestMethod.POST)	@ResponseBody	public Map
    
      testrequestBody(@RequestBody Map
     
       map1){		Map
      
        map=new HashMap
       
        ();		map.put("name","lg");		map.put("age",23);		map.put("date",new Date());		return map;	}
       
      
     
    

HttpEntityMethodProcessor具体的解析参数的过程：

@Override	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,			NativeWebRequest webRequest, WebDataBinderFactory binderFactory)			throws IOException, HttpMediaTypeNotSupportedException {		HttpInputMessage inputMessage = createInputMessage(webRequest);		Type paramType = getHttpEntityType(parameter);		Object body = readWithMessageConverters(webRequest, parameter, paramType);		return new HttpEntity

就是通过HttpMessageConverter来进一步的判断是否支持HttpEntity<T>中我们想要的T类型以及是否支持相应的content-type，如public Map<String,Object> testHttp(HttpEntity<String> httpEntity) ，则会选择StringHttpMessageConverter来进行转换。具体的选择过程如下：

protected 
    
      Object readWithMessageConverters(HttpInputMessage inputMessage,			MethodParameter methodParam, Type targetType) throws IOException, HttpMediaTypeNotSupportedException {		MediaType contentType;		try {			contentType = inputMessage.getHeaders().getContentType();		}		catch (InvalidMediaTypeException ex) {			throw new HttpMediaTypeNotSupportedException(ex.getMessage());		}		if (contentType == null) {			contentType = MediaType.APPLICATION_OCTET_STREAM;		}		Class
      contextClass = methodParam.getContainingClass();		for (HttpMessageConverter
      converter : this.messageConverters) {			if (converter instanceof GenericHttpMessageConverter) {				GenericHttpMessageConverter
      genericConverter = (GenericHttpMessageConverter
     ) converter;				if (genericConverter.canRead(targetType, contextClass, contentType)) {					if (logger.isDebugEnabled()) {						logger.debug("Reading [" + targetType + "] as \"" +								contentType + "\" using [" + converter + "]");					}					return genericConverter.read(targetType, contextClass, inputMessage);				}			}			Class
     
       targetClass = (Class
      
       )					ResolvableType.forMethodParameter(methodParam, targetType).resolve(Object.class);			if (converter.canRead(targetClass, contentType)) {				if (logger.isDebugEnabled()) {					logger.debug("Reading [" + targetClass.getName() + "] as \"" +							contentType + "\" using [" + converter + "]");				}				return ((HttpMessageConverter
       
        ) converter).read(targetClass, inputMessage);			}		}		throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);	}
       
      
     
    

同理RequestResponseBodyMethodProcessor也会使用相应的HttpMessageConverter来进行转换。如public Map<String,Object> testrequestBody(@RequestBody Map<String,Object> map1)则会选择MappingJackson2HttpMessageConverter或者MappingJacksonHttpMessageConverter来完成转换。

再看看另一类的HandlerMethodArgumentResolver：

RequestParamMethodArgumentResolver支持的类型有，一种是含@RequestParam注解的参数，另一种就是简单类型，如Integer、String、Date、URI, URL,Locale等：

源代码如下：

public boolean supportsParameter(MethodParameter parameter) {		Class
     paramType = parameter.getParameterType();		if (parameter.hasParameterAnnotation(RequestParam.class)) {			if (Map.class.isAssignableFrom(paramType)) {				String paramName = parameter.getParameterAnnotation(RequestParam.class).value();				return StringUtils.hasText(paramName);			}			else {				return true;			}		}		else {			if (parameter.hasParameterAnnotation(RequestPart.class)) {				return false;			}			else if (MultipartFile.class.equals(paramType) || "javax.servlet.http.Part".equals(paramType.getName())) {				return true;			}			else if (this.useDefaultResolution) {				return BeanUtils.isSimpleProperty(paramType);			}			else {				return false;			}		}	}

BeanUtils.isSimpleProperty(paramType)判断是否是简单类型的具体内容如下：

/**	 * Check if the given type represents a "simple" property:	 * a primitive, a String or other CharSequence, a Number, a Date,	 * a URI, a URL, a Locale, a Class, or a corresponding array.	 * 
Used to determine properties to check for a "simple" dependency-check.	 * @param clazz the type to check	 * @return whether the given type represents a "simple" property	 * @see org.springframework.beans.factory.support.RootBeanDefinition#DEPENDENCY_CHECK_SIMPLE	 * @see org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#checkDependencies	 */	public static boolean isSimpleProperty(Class
      clazz) {		Assert.notNull(clazz, "Class must not be null");		return isSimpleValueType(clazz) || (clazz.isArray() && isSimpleValueType(clazz.getComponentType()));	}public static boolean isSimpleValueType(Class
      clazz) {		return ClassUtils.isPrimitiveOrWrapper(clazz) || clazz.isEnum() ||				CharSequence.class.isAssignableFrom(clazz) ||				Number.class.isAssignableFrom(clazz) ||				Date.class.isAssignableFrom(clazz) ||				clazz.equals(URI.class) || clazz.equals(URL.class) ||				clazz.equals(Locale.class) || clazz.equals(Class.class);	}

即当请求为 http://localhost:8080/test?name=abc时，处理函数若为test(String name)，则对name的解析就是采用RequestParamMethodArgumentResolver来解析的。

RequestHeaderMethodArgumentResolver:主要用来处理含有@RequestHeader注解的参数，但同时该参数又不是Map类型。如下：

@Override	public boolean supportsParameter(MethodParameter parameter) {		return parameter.hasParameterAnnotation(RequestHeader.class)				&& !Map.class.isAssignableFrom(parameter.getParameterType());	}	@Override	protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {		String[] headerValues = request.getHeaderValues(name);		if (headerValues != null) {			return (headerValues.length == 1 ? headerValues[0] : headerValues);		}		else {			return null;		}	}

源代码已经说明的很明白了。

使用场景：

@RequestMapping(value="/test/requestHeader",method=RequestMethod.GET)	@ResponseBody	public Map
    
      testrequestHeader(@RequestHeader String  Accept){
    

若想获取所有的header信息：则使用另一个RequestHeaderMapMethodArgumentResolver，它则用来获取所有的header信息：

public class RequestHeaderMapMethodArgumentResolver implements HandlerMethodArgumentResolver {//这里已经写明白了，要求参数必须含有@RequestHeader注解，并且是Map类型	@Override	public boolean supportsParameter(MethodParameter parameter) {		return parameter.hasParameterAnnotation(RequestHeader.class)				&& Map.class.isAssignableFrom(parameter.getParameterType());	}	@Override	public Object resolveArgument(			MethodParameter parameter, ModelAndViewContainer mavContainer,			NativeWebRequest webRequest, WebDataBinderFactory binderFactory)			throws Exception {		Class
     paramType = parameter.getParameterType();		if (MultiValueMap.class.isAssignableFrom(paramType)) {			MultiValueMap
    
      result;			if (HttpHeaders.class.isAssignableFrom(paramType)) {				result = new HttpHeaders();			}			else {				result = new LinkedMultiValueMap
     
      ();			}			for (Iterator
      
        iterator = webRequest.getHeaderNames(); iterator.hasNext();) {				String headerName = iterator.next();				for (String headerValue : webRequest.getHeaderValues(headerName)) {					result.add(headerName, headerValue);				}			}			return result;		}		else {			Map
       
         result = new LinkedHashMap
        
         ();			for (Iterator
         
           iterator = webRequest.getHeaderNames(); iterator.hasNext();) { String headerName = iterator.next(); String headerValue = webRequest.getHeader(headerName); result.put(headerName, headerValue); } return result; } }}
         
        
       
      
     
    

从上面的解析过程可以看出，参数类型可以是普通的Map类型，也可以是MultiValueMap或者进一步的HttpHeaders，他们与普通Map类型的区别是他们对value值后者们是以List形式存放，前者是以String形式存放。

使用场景：

@RequestMapping(value="/test/requestHeader",method=RequestMethod.GET)	@ResponseBody	public Map
    
      testrequestHeader(@RequestHeader Map
     
       map1){public Map
      
        testrequestHeader(@RequestHeader MultiValueMap
       
         map1){
       
      
     
    

PathVariableMethodArgumentResolver:主要针对含有@PathVariable的参数，代码如下：

@Override	public boolean supportsParameter(MethodParameter parameter) {		if (!parameter.hasParameterAnnotation(PathVariable.class)) {			return false;		}		if (Map.class.isAssignableFrom(parameter.getParameterType())) {			String paramName = parameter.getParameterAnnotation(PathVariable.class).value();			return StringUtils.hasText(paramName);		}		return true;	}@Override	@SuppressWarnings("unchecked")	protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {		Map
    
      uriTemplateVars =			(Map
     
      ) request.getAttribute(					HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);		return (uriTemplateVars != null) ? uriTemplateVars.get(name) : null;	}
     
    

对于支持的类型也说明的很详细。首先必须含有@PathVariable注解，其次如果是Map类型，必须要指定@PathVariable的值，即这个

ArgumentResolver只能获取一个uri变量。要想获取多个则要使用PathVariableMapMethodArgumentResolver：

@Override	public boolean supportsParameter(MethodParameter parameter) {		PathVariable annot = parameter.getParameterAnnotation(PathVariable.class);		return ((annot != null) && (Map.class.isAssignableFrom(parameter.getParameterType()))				&& (!StringUtils.hasText(annot.value())));	}public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {		@SuppressWarnings("unchecked")		Map
    
      uriTemplateVars =				(Map
     
      ) webRequest.getAttribute(						HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);		if (!CollectionUtils.isEmpty(uriTemplateVars)) {			return new LinkedHashMap
      
       (uriTemplateVars);		}		else {			return Collections.emptyMap();		}	}
      
     
    

它要求必须含有@PathVariable注解，并且必须是Map类型，并且@PathVariable注解的value没有值。同时我们可以从PathVariableMapMethodArgumentResolver和PathVariableMethodArgumentResolver上面看出，他们的取值都是从request的属性上进行获取的webRequest.getAttribute(

HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);也就是说，在解析完@RequestMapping匹配工作后，便将这些参数设置进request的属性上，属性名为HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE。其他的HandlerMethodArgumentResolver可以自行研究，这里不再说明。

至此，我们就要说明下HandlerMethodArgumentResolver的注册来源：

它的来源分为两部分，一部分spring默认的HandlerMethodArgumentResolver，另一部分就是我们自定义的HandlerMethodArgumentResolver。

还是先看mvc:annotation-driven中配置自定义的HandlerMethodArgumentResolver：

在mvc:argument-resolvers标签下配置相应的自定义的HandlerMethodArgumentResolver。

然后在mvc:annotation-driven的注解驱动类AnnotationDrivenBeanDefinitionParser中会有这样的代码：

ManagedList
     argumentResolvers = getArgumentResolvers(element, parserContext);//略if (argumentResolvers != null) {			handlerAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);		}

其中getArgumentResolvers就是获取我们自定义的HandlerMethodArgumentResolver

private ManagedList
     getArgumentResolvers(Element element, ParserContext parserContext) {		Element resolversElement = DomUtils.getChildElementByTagName(element, "argument-resolvers");		if (resolversElement != null) {			ManagedList
    
      argumentResolvers = extractBeanSubElements(resolversElement, parserContext);			return wrapWebArgumentResolverBeanDefs(argumentResolvers, parserContext);		}		return null;	}
    

从上面的代码可以看出，获取我们自定义的HandlerMethodArgumentResolver然后把它设置进RequestMappingHandlerAdapter的customArgumentResolvers参数中，RequestMappingHandlerAdapter有两个与HandlerMethodArgumentResolver有关的参数：

private List
    
      customArgumentResolvers;private HandlerMethodArgumentResolverComposite argumentResolvers;
    

HandlerMethodArgumentResolverComposite 也仅仅是内部存放一个List<HandlerMethodArgumentResolver>集合，同时本身又继承HandlerMethodArgumentResolver，所以它的实现都是靠内部的List<HandlerMethodArgumentResolver>集合来实现的。

private final List
    
      argumentResolvers =			new LinkedList
     
      ();//使用了适合高并发的ConcurrentHashMap来进行缓存	private final Map
      
        argumentResolverCache =			new ConcurrentHashMap
       
        (256);	/**	 * Return a read-only list with the contained resolvers, or an empty list.	 */	public List
        
          getResolvers() {		return Collections.unmodifiableList(this.argumentResolvers);	}	/**	 * Whether the given {@linkplain MethodParameter method parameter} is supported by any registered	 * {@link HandlerMethodArgumentResolver}.	 */	@Override	public boolean supportsParameter(MethodParameter parameter) {		return getArgumentResolver(parameter) != null;	}	/**	 * Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it.	 * @exception IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found.	 */	@Override	public Object resolveArgument(			MethodParameter parameter, ModelAndViewContainer mavContainer,			NativeWebRequest webRequest, WebDataBinderFactory binderFactory)			throws Exception {		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);		Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");		return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);	}	/**	 * Find a registered {@link HandlerMethodArgumentResolver} that supports the given method parameter.	 */	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;	}
        
       
      
     
    

在RequestMappingHandlerAdapter完成参数设置后，会调用afterPropertiesSet方法

@Override	public void afterPropertiesSet() {		if (this.argumentResolvers == null) {			List
    
      resolvers = getDefaultArgumentResolvers();			this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);		}		if (this.initBinderArgumentResolvers == null) {			List
     
       resolvers = getDefaultInitBinderArgumentResolvers();			this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);		}		if (this.returnValueHandlers == null) {			List
      
        handlers = getDefaultReturnValueHandlers();			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);		}		initControllerAdviceCache();	}
      
     
    

getDefaultArgumentResolvers方法完成了所有的HandlerMethodArgumentResolver的汇总，如下：

private List
    
      getDefaultArgumentResolvers() {		List
     
       resolvers = new ArrayList
      
       ();		// Annotation-based argument resolution		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));		resolvers.add(new RequestParamMapMethodArgumentResolver());		resolvers.add(new PathVariableMethodArgumentResolver());		resolvers.add(new PathVariableMapMethodArgumentResolver());		resolvers.add(new MatrixVariableMethodArgumentResolver());		resolvers.add(new MatrixVariableMapMethodArgumentResolver());		resolvers.add(new ServletModelAttributeMethodProcessor(false));		resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters()));		resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters()));		resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));		resolvers.add(new RequestHeaderMapMethodArgumentResolver());		resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));		resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));		// Type-based argument resolution		resolvers.add(new ServletRequestMethodArgumentResolver());		resolvers.add(new ServletResponseMethodArgumentResolver());		resolvers.add(new HttpEntityMethodProcessor(getMessageConverters()));		resolvers.add(new RedirectAttributesMethodArgumentResolver());		resolvers.add(new ModelMethodProcessor());		resolvers.add(new MapMethodProcessor());		resolvers.add(new ErrorsMethodArgumentResolver());		resolvers.add(new SessionStatusMethodArgumentResolver());		resolvers.add(new UriComponentsBuilderMethodArgumentResolver());		// Custom arguments//获取我们自定义的HandlerMethodArgumentResolver		if (getCustomArgumentResolvers() != null) {			resolvers.addAll(getCustomArgumentResolvers());		}		// Catch-all		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));		resolvers.add(new ServletModelAttributeMethodProcessor(true));		return resolvers;	}
      
     
    

不仅汇总了spring默认的，同时加进来我们自定义的HandlerMethodArgumentResolver。至此，HandlerMethodArgumentResolver的来龙去脉都说清楚了。然后就是我们自定义HandlerMethodArgumentResolver,下一篇文章再说。