Spring 源码学习（十四）—— HandlerMethodArgumentResolver
HandlerMethodArgumentResolver 对象用于向外提供处理器方法参数解析，其提供了 supportsParameter 方法与 resolveArgument 两个方法，分别用于判断参数的支持度与方法参数的解析；
public interface HandlerMethodArgumentResolver {boolean supportsParameter(MethodParameter parameter);@NullableObject resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;}HandlerMethodArgumentResolver 接口拥有许多实现，本文不会全部介绍，只会挑选其中重要的实现进行介绍。
1. HandlerMethodArgumentResolverComposite
1.1 属性
HandlerMethodArgumentResolverComposite 类用于将多个 HandlerMethodArgumentResolver 组合到一起使用，其拥有两个属性，一个用于保存所有的 HandlerMethodArgumentResolver 对象组合，另一个则是参数解析器缓存。
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {private final List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>();private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =new ConcurrentHashMap<>(256);public HandlerMethodArgumentResolverComposite addResolver(HandlerMethodArgumentResolver resolver) {this.argumentResolvers.add(resolver);return this;}public HandlerMethodArgumentResolverComposite addResolvers(@Nullable HandlerMethodArgumentResolver... resolvers) {if (resolvers != null) {Collections.addAll(this.argumentResolvers, resolvers);}return this;}public HandlerMethodArgumentResolverComposite addResolvers(@Nullable List<? extends HandlerMethodArgumentResolver> resolvers) {if (resolvers != null) {this.argumentResolvers.addAll(resolvers);}return this;}public List<HandlerMethodArgumentResolver> getResolvers() {return Collections.unmodifiableList(this.argumentResolvers);}public void clear() {this.argumentResolvers.clear();}
}1.2 方法
HandlerMethodArgumentResolverComposite 的 supportsParameter 与 resolveArgument 方法实现都是通过 getArgumentResolver 方法获取对应解析器，然后在执行对应动作；
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return getArgumentResolver(parameter) != null;}@Override@Nullablepublic Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);if (resolver == null) {throw new IllegalArgumentException("Unsupported parameter type [" +parameter.getParameterType().getName() + "]. supportsParameter should be called first.");}return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);}
}1.2.1 getArgumentResolver 方法
getArgumentResolver 方法则首先从 argumentResolverCache 中获取对应解析器，没获取到才会遍历 argumentResolvers 参数，通过 supportsParameter 方法获取对应解析器，保存至 argumentResolvers 缓存并返回。
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {@Nullableprivate HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);if (result == null) {for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {if (resolver.supportsParameter(parameter)) {result = resolver;this.argumentResolverCache.put(parameter, result);break;}}}return result;}
}2. RequestResponseBodyMethodProcessor
RequestResponseBodyMethodProcessor 类拥有两个功能，一个是对 RequestBody 请求参数进行解析，另一个则是处理 ResponseBody 响应结果；由于本文只是针对 HandlerMethodArgumentResolver 方法参数处理器的实现进行分析，因此只会对请求参数解析流程进行分析，对应返参处理流程的分析（AbstractMessageConverterMethodProcessor 中定义的方法及 handleReturnValue 相关方法）将会在后续 HandlerMethodReturnValueHandler 返回值处理器接口及其实现中进行；
2.0 流程概览
2.1 AbstractMessageConverterMethodArgumentResolver 抽象类
AbstractMessageConverterMethodArgumentResolver 类为将请求体解析为方法的基类；其只提供了一些请求体交互的方法而未提供任何 HandlerMethodArgumentResolver 接口方法的实现。
2.1.1 属性
常量
AbstractMessageConverterMethodArgumentResolver 类拥有两个常量，其一是 SUPPORTED_METHODS 所支持的方法，包含 POST、PUT 以及 PATCH，另一个则是用于标识请求体无任何内容的 NO_VALUE。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {private static final Set<HttpMethod> SUPPORTED_METHODS =EnumSet.of(HttpMethod.POST, HttpMethod.PUT, HttpMethod.PATCH);private static final Object NO_VALUE = new Object();
}类变量
AbstractMessageConverterMethodArgumentResolver 拥有三个变量，分别为可用的 http 消息转换器列表 messageConverters 用于提取请求体内容，支持的媒体类型列表 allSupportedMediaTypes 及请求响应体处理器切面链 advice。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {protected final List<HttpMessageConverter<?>> messageConverters;protected final List<MediaType> allSupportedMediaTypes;private final RequestResponseBodyAdviceChain advice;RequestResponseBodyAdviceChain getAdvice() {return this.advice;}
}2.1.2 方法
构造方法
创建 AbstractMessageConverterMethodArgumentResolver 对象需要两个参数 converters 消息转换器列表与请求响应体切面处理器列表 requestResponseBodyAdvice，其中 converters 是必须的，其除了用于直接为 messageConverters 属性赋值外，还未调用 getAllSupportedMediaTypes 方法获取其所能解析的所有媒体列表并保存到 allSupportedMediaTypes 属性之中，而 requestResponseBodyAdvice 在使用 RequestResponseBodyAdviceChain 封装后保存至 advice 属性之中。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {public AbstractMessageConverterMethodArgumentResolver(List<HttpMessageConverter<?>> converters) {this(converters, null);}public AbstractMessageConverterMethodArgumentResolver(List<HttpMessageConverter<?>> converters,@Nullable List<Object> requestResponseBodyAdvice) {Assert.notEmpty(converters, "'messageConverters' must not be empty");this.messageConverters = converters;this.allSupportedMediaTypes = getAllSupportedMediaTypes(converters);this.advice = new RequestResponseBodyAdviceChain(requestResponseBodyAdvice);}
}getAllSupportedMediaTypes 方法依次获取 messageConverters 列表中所有对应的 MediaType 媒体类型，在去重、排序后返回。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {private static List<MediaType> getAllSupportedMediaTypes(List<HttpMessageConverter<?>> messageConverters) {Set<MediaType> allSupportedMediaTypes = new LinkedHashSet<>();for (HttpMessageConverter<?> messageConverter : messageConverters) {allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes());}List<MediaType> result = new ArrayList<>(allSupportedMediaTypes);MediaType.sortBySpecificity(result);return Collections.unmodifiableList(result);}
}readWithMessageConverters 方法
readWithMessageConverters 方法为 AbstractMessageConverterMethodArgumentResolver 类的核心方法，其提供了核心功能，即将请求体读取为指定对象并返回，其拥有两个不同的重载，一个是从 NativeWebRequest 类型的请求体中读取数据，另一个则是从 HttpInputMessage 中解析对象。
从 NativeWebRequest 类型的请求体中读取数据首先调用 createInputMessage 方法使用 NativeWebRequest 构建 HttpInputMessage 对象，并调用另一个 readWithMessageConverters 方法继续读取并返回；
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {@Nullableprotected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter,Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {HttpInputMessage inputMessage = createInputMessage(webRequest);return readWithMessageConverters(inputMessage, parameter, paramType);}
}readWithMessageConverters 方法首先获取 inputMessage 请求的内容类型，若未设置，则会赋值为 APPLICATION_OCTET_STREAM；随后获取 parameter 参数的上下文类型 Class 对象及本身对象类型类对象；随后选取支持类型与媒体类型的消息转换器，在 message 拥有请求体是，依次使用切面的 beforeBodyRead 进行切面前置处理，消息转换器的 read 方法获取对象及切面的 afterBodyRead 方法进行后处理并将最终结果保存到 body 变量之中，在 message 没有请求体时，直接调用切面的 handleEmptyBody 方法进行处理空请求体并将其结果保存至 body 变量之中，最后若 body 不为 NO_VALUE 直接返回该变量值，否则在 httpMethod 为空、httpMethod 不在 SUPPORTED_METHODS 中或满足没有请求体的同时没有媒体类型标识时直接返回 null，不满足上述所有条件则会直接抛出异常。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {@Nullableprotected <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.getContainingClass();Class<T> targetClass = (targetType instanceof Class ? (Class<T>) targetType : null);if (targetClass == null) {ResolvableType resolvableType = ResolvableType.forMethodParameter(parameter);targetClass = (Class<T>) resolvableType.resolve();}HttpMethod httpMethod = (inputMessage instanceof HttpRequest ? ((HttpRequest) inputMessage).getMethod() : null);Object body = NO_VALUE;EmptyBodyCheckingHttpInputMessage message;try {message = new EmptyBodyCheckingHttpInputMessage(inputMessage);for (HttpMessageConverter<?> converter : this.messageConverters) {Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();GenericHttpMessageConverter<?> genericConverter =(converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) :(targetClass != null && converter.canRead(targetClass, contentType))) {if (message.hasBody()) {HttpInputMessage msgToUse =getAdvice().beforeBodyRead(message, parameter, targetType, converterType);body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);}else {body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);}break;}}}catch (IOException ex) {throw new HttpMessageNotReadableException("I/O error while reading input message", ex, inputMessage);}if (body == NO_VALUE) {if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||(noContentType && !message.hasBody())) {return null;}throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);}MediaType selectedContentType = contentType;Object theBody = body;LogFormatUtils.traceDebug(logger, traceOn -> {String formatted = LogFormatUtils.formatValue(theBody, !traceOn);return "Read \"" + selectedContentType + "\" to [" + formatted + "]";});return body;}
}createInputMessage 方法
createInputMessage 方法在 webRequest 为 HttpServletRequest 对象时直接使用 ServletServerHttpRequest 对其进行封装并返回，否则抛出异常。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {protected ServletServerHttpRequest createInputMessage(NativeWebRequest webRequest) {HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);Assert.state(servletRequest != null, "No HttpServletRequest");return new ServletServerHttpRequest(servletRequest);}
}validateIfApplicable 方法
validateIfApplicable 方法用于方法参数的验证，通过参数的 Validated 注解或名为 Valid 开头注解对象的 value 属性值与 binder 参数的 validate 方法来进行验证。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {Annotation[] annotations = parameter.getParameterAnnotations();for (Annotation ann : annotations) {Validated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);if (validatedAnn != null || ann.annotationType().getSimpleName().startsWith("Valid")) {Object hints = (validatedAnn != null ? validatedAnn.value() : AnnotationUtils.getValue(ann));Object[] validationHints = (hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});binder.validate(validationHints);break;}}}
}isBindExceptionRequired 方法
isBindExceptionRequired 方法用于判断当前参数是否没有指定的绑定异常；其是通过判断当前参数的后续参数是否不为 Error 的子类进行判断的。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {protected boolean isBindExceptionRequired(WebDataBinder binder, MethodParameter parameter) {int i = parameter.getParameterIndex();Class<?>[] paramTypes = parameter.getExecutable().getParameterTypes();boolean hasBindingResult = (paramTypes.length > (i + 1) && Errors.class.isAssignableFrom(paramTypes[i + 1]));return !hasBindingResult;}
}adaptArgumentIfNecessary 方法
adaptArgumentIfNecessary 方法用于适配 Optional 类型参数。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {@Nullableprotected Object adaptArgumentIfNecessary(@Nullable Object arg, MethodParameter parameter) {if (parameter.getParameterType() == Optional.class) {if (arg == null || (arg instanceof Collection && ((Collection<?>) arg).isEmpty()) ||(arg instanceof Object[] && ((Object[]) arg).length == 0)) {return Optional.empty();}else {return Optional.of(arg);}}return arg;}
}2.1.3 内部类
EmptyBodyCheckingHttpInputMessage 类
EmptyBodyCheckingHttpInputMessage 类为 HttpInputMessage 实现类，其用于封装指定 inputMessage，扩展了空请求体检验功能。
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {private static class EmptyBodyCheckingHttpInputMessage implements HttpInputMessage {private final HttpHeaders headers;@Nullableprivate final InputStream body;public EmptyBodyCheckingHttpInputMessage(HttpInputMessage inputMessage) throws IOException {this.headers = inputMessage.getHeaders();InputStream inputStream = inputMessage.getBody();if (inputStream.markSupported()) {inputStream.mark(1);this.body = (inputStream.read() != -1 ? inputStream : null);inputStream.reset();}else {PushbackInputStream pushbackInputStream = new PushbackInputStream(inputStream);int b = pushbackInputStream.read();if (b == -1) {this.body = null;}else {this.body = pushbackInputStream;pushbackInputStream.unread(b);}}}@Overridepublic HttpHeaders getHeaders() {return this.headers;}@Overridepublic InputStream getBody() {return (this.body != null ? this.body : StreamUtils.emptyInput());}public boolean hasBody() {return (this.body != null);}}
}2.2 resolveArgument 方法
resolveArgument 方法首先通过 readWithMessageConverters 方法解析 webRequest 请求体并将解析结果保存到 arg 变量中并使用 Conventions 的 getVariableNameForParameter 生成参数对应的对象名；在 binderFactory 不为空时首先调用其 createBinder 方法创建对应数据绑定器，之后若 arg 解析参数不为空，依次调用 validateIfApplicable 与 isBindExceptionRequired 方法进行参数的验证，判断是否直接抛出异常，随后在 mavContainer 参数不为空时，直接将参数结果保存绑定到其 BindingResult.MODEL_KEY_PREFIX + name 属性上，最后调用 adaptArgumentIfNecessary 参数适配 Optional 参数。
public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {@Overridepublic Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {parameter = parameter.nestedIfOptional();Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());String name = Conventions.getVariableNameForParameter(parameter);if (binderFactory != null) {WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);if (arg != null) {validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());}}if (mavContainer != null) {mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());}}return adaptArgumentIfNecessary(arg, parameter);}
}2.3 readWithMessageConverters 方法
RequestResponseBodyMethodProcessor 类除了实现了 resolveArgument 方法时，还重写了 AbstractMessageConverterMethodArgumentResolver 抽象类的 readWithMessageConverters 方法用于支持参数的必填验证，参数的必填验证时通过 checkRequired 方法进行的，checkRequired 方法直接返回参数 RequestBody 注解的 required 方法值且是否不为 Optional 对象。
public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {@Overrideprotected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter,Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);Assert.state(servletRequest != null, "No HttpServletRequest");ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);Object arg = readWithMessageConverters(inputMessage, parameter, paramType);if (arg == null && checkRequired(parameter)) {throw new HttpMessageNotReadableException("Required request body is missing: " +parameter.getExecutable().toGenericString(), inputMessage);}return arg;}protected boolean checkRequired(MethodParameter parameter) {RequestBody requestBody = parameter.getParameterAnnotation(RequestBody.class);return (requestBody != null && requestBody.required() && !parameter.isOptional());}
}3. AbstractNamedValueMethodArgumentResolver 抽象类
AbstractNamedValueMethodArgumentResolver 为所有从各种"命名值"（named values）中解析控制器方法的参数值解析器通用父类；
3.0 流程概览
3.1 属性
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {@Nullableprivate final ConfigurableBeanFactory configurableBeanFactory;@Nullableprivate final BeanExpressionContext expressionContext;private final Map<MethodParameter, NamedValueInfo> namedValueInfoCache = new ConcurrentHashMap<>(256);
}AbstractNamedValueMethodArgumentResolver 类有三个属性，分别为 configurableBeanFactory 对象工厂、对象表达式上下文 expressionContext 及 namedValueInfoCache 命名值缓存。
3.2 方法
3.2.1 构造方法
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {public AbstractNamedValueMethodArgumentResolver() {this.configurableBeanFactory = null;this.expressionContext = null;}public AbstractNamedValueMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {this.configurableBeanFactory = beanFactory;this.expressionContext =(beanFactory != null ? new BeanExpressionContext(beanFactory, new RequestScope()) : null);}
}AbstractNamedValueMethodArgumentResolver 抽象类拥有 2 个构造方法，无参构造方法将属性置为 null，传入 beanFactory 对象工厂的构造方法在为 configurableBeanFactory 参数赋值的同时使用对象工厂构建 BeanExpressionContext 表达式上下文对象用于初始化 expressionContext 属性。
3.2.2 resolveArgument 方法
resolveArgument 方法首先调用 getNamedValueInfo 方法获取对应的 NamedValueInfo 对象，随后调用 parameter 参数的 nestedIfOptional 方法获取实际参数对象；并在之后调用 resolveEmbeddedValuesAndExpressions 方法解析参数名中占位符以及表达式，随后调用 resolveName 从指定位置处获取解析得到对应参数值并保存到 arg 变量之中，在未解析获取到任何值时且参数为必须时，直接调用 handleMissingValue 方法处理未查到参数异常，在其为空或空字符串且拥有默认值时，调用 resolveEmbeddedValuesAndExpressions 方法对默认值进行解析并更新到 arg 属性之中，否则在 arg 为 null 时调用 handleNullValue 方法对空参数值进行处理；随后使用 binderFactory 数据绑定工厂创建 WebDataBinder 数据绑定器对象并调用其 convertIfNecessary 方法将 arg 参数值转换为对应类型数据，最后调用 handleResolvedValue 方法进一步处理完成解析的参数并返回。
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {@Override@Nullablepublic final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);MethodParameter nestedParameter = parameter.nestedIfOptional();Object resolvedName = resolveEmbeddedValuesAndExpressions(namedValueInfo.name);if (resolvedName == null) {throw new IllegalArgumentException("Specified name must not resolve to null: [" + namedValueInfo.name + "]");}Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest);if (arg == null) {if (namedValueInfo.defaultValue != null) {arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue);}else if (namedValueInfo.required && !nestedParameter.isOptional()) {handleMissingValue(namedValueInfo.name, nestedParameter, webRequest);}arg = handleNullValue(namedValueInfo.name, arg, nestedParameter.getNestedParameterType());}else if ("".equals(arg) && namedValueInfo.defaultValue != null) {arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue);}if (binderFactory != null) {WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);try {arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);}catch (ConversionNotSupportedException ex) {throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(),namedValueInfo.name, parameter, ex.getCause());}catch (TypeMismatchException ex) {throw new MethodArgumentTypeMismatchException(arg, ex.getRequiredType(),namedValueInfo.name, parameter, ex.getCause());}}handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);return arg;}@Nullableprotected abstract Object resolveName(String name, MethodParameter parameter, NativeWebRequest request)throws Exception;@Nullableprivate Object handleNullValue(String name, @Nullable Object value, Class<?> paramType) {if (value == null) {if (Boolean.TYPE.equals(paramType)) {return Boolean.FALSE;}else if (paramType.isPrimitive()) {throw new IllegalStateException("Optional " + paramType.getSimpleName() + " parameter '" + name +"' is present but cannot be translated into a null value due to being declared as a " +"primitive type. Consider declaring it as object wrapper for the corresponding primitive type.");}}return value;}protected void handleResolvedValue(@Nullable Object arg, String name, MethodParameter parameter,@Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest) {}
}getNamedValueInfo 方法首先尝试从 namedValueInfoCache 缓存中获取 NamedValueInfo 对象，在其不为空时直接返回；为空则会依次调用 createNamedValueInfo 方法创建并更新 NamedValueInfo 对象值，并保存至 namedValueInfoCache 缓存后返回。
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {private NamedValueInfo getNamedValueInfo(MethodParameter parameter) {NamedValueInfo namedValueInfo = this.namedValueInfoCache.get(parameter);if (namedValueInfo == null) {namedValueInfo = createNamedValueInfo(parameter);namedValueInfo = updateNamedValueInfo(parameter, namedValueInfo);this.namedValueInfoCache.put(parameter, namedValueInfo);}return namedValueInfo;}protected abstract NamedValueInfo createNamedValueInfo(MethodParameter parameter);
}updateNamedValueInfo 方法主要目的是在 info 没有对应名称时将其更新为方法名，在其不存在默认值时将其默认值更新为 null。
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {String name = info.name;if (info.name.isEmpty()) {name = parameter.getParameterName();if (name == null) {throw new IllegalArgumentException("Name for argument of type [" + parameter.getNestedParameterType().getName() +"] not specified, and parameter name information not found in class file either.");}}String defaultValue = (ValueConstants.DEFAULT_NONE.equals(info.defaultValue) ? null : info.defaultValue);return new NamedValueInfo(name, info.required, defaultValue);}
}resolveEmbeddedValuesAndExpressions 方法用于解析参数中的占位符与 spring SpEL 表达式，其只有在 configurableBeanFactory 或 expressionContext 属性都不为空时才会进行解析，否则直接返回 value 参数值，其首先调用 configurableBeanFactory 对象工厂的 resolveEmbeddedValue 方法解析 value 中的 ${..} 占位符，随后调用 configurableBeanFactory 对象工厂中的 BeanExpressionResolver 表达式解析器的 evaluate 方法解析 #{expression} placeholdersResolved 变量中的 SpEL 表达式并返回解析结果。
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {@Nullableprivate Object resolveEmbeddedValuesAndExpressions(String value) {if (this.configurableBeanFactory == null || this.expressionContext == null) {return value;}String placeholdersResolved = this.configurableBeanFactory.resolveEmbeddedValue(value);BeanExpressionResolver exprResolver = this.configurableBeanFactory.getBeanExpressionResolver();if (exprResolver == null) {return value;}return exprResolver.evaluate(placeholdersResolved, this.expressionContext);}
}3.3 内部类
3.3.1 NamedValueInfo 类
NamedValueInfo 方法用于标识参数的相关元数据，其中 name 为参数名称，required 属性标识是否必须，defaultValue 则是参数默认值。
public abstract class AbstractNamedValueMethodArgumentResolver implements HandlerMethodArgumentResolver {protected static class NamedValueInfo {private final String name;private final boolean required;@Nullableprivate final String defaultValue;public NamedValueInfo(String name, boolean required, @Nullable String defaultValue) {this.name = name;this.required = required;this.defaultValue = defaultValue;}}
}4 RequestParamMethodArgumentResolver 类
RequestParamMethodArgumentResolver 类用于 RequestParam 注解修饰的方法参数的解析。
4.1 属性
4.1.1 常量
RequestParamMethodArgumentResolver 类只有个保存字符串类型描述符的 STRING_TYPE_DESCRIPTOR 常量。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {private static final TypeDescriptor STRING_TYPE_DESCRIPTOR = TypeDescriptor.valueOf(String.class);
}4.1.2 类变量
RequestParamMethodArgumentResolver 类也只有一个开关，用于标识当前解析器是否为默认解析器，主要标识是否可用于未获取到对应解析器的参数的解析。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {private final boolean useDefaultResolution;
}4.2 方法
4.2.1 构造方法
RequestParamMethodArgumentResolver 类拥有两个构造方法，其提供了使用 ConfigurableBeanFactory 与 useDefaultResolution 标识创建对象；
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {public RequestParamMethodArgumentResolver(boolean useDefaultResolution) {this.useDefaultResolution = useDefaultResolution;}public RequestParamMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory,boolean useDefaultResolution) {super(beanFactory);this.useDefaultResolution = useDefaultResolution;}
}4.2.2 supportsParameter 方法
supportsParameter 方法在参数拥有 RequestParam 注解时，参数类型不是 Map 直接返回，否则将会判断 RequestParam 对象是否拥有 name 值，只有拥有 name 属性值才会返回 true；而在没有 RequestParam 注解时，则首先会判断是否拥有 RequestPart 注解，拥有时直接返回 false，在参数为 Multipart 类型或其数组时也直接返回 true，否则只有在 useDefaultResolution 属性为 true 且参数为简单类型（基本数据类型及其包装类、常见标准类型如 String、Number、Date、URI、URL、Locale、Class 等或枚举类型）或其数组时才会返回 true，否则返回 false。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overridepublic boolean supportsParameter(MethodParameter parameter) {if (parameter.hasParameterAnnotation(RequestParam.class)) {if (Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);return (requestParam != null && StringUtils.hasText(requestParam.name()));}else {return true;}}else {if (parameter.hasParameterAnnotation(RequestPart.class)) {return false;}parameter = parameter.nestedIfOptional();if (MultipartResolutionDelegate.isMultipartArgument(parameter)) {return true;}else if (this.useDefaultResolution) {return BeanUtils.isSimpleProperty(parameter.getNestedParameterType());}else {return false;}}}
}4.2.3 createNamedValueInfo 方法
createNamedValueInfo 方法在参数的 RequestParam 注解不为空时，使用注解对象创建 RequestParamNamedValueInfo 对象，为空时创建空 RequestParamNamedValueInfo 对象并返回。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {RequestParam ann = parameter.getParameterAnnotation(RequestParam.class);return (ann != null ? new RequestParamNamedValueInfo(ann) : new RequestParamNamedValueInfo());}
}4.2.4 resolveName 方法
resolveName 方法首先尝试将 request 请求转换为 HttpServletRequest 对象，在其不为空时，判断是否请求参数是否为 Mutipart 类型，若是则直接返回解析的 Mutipart 类型解析结果；之后尝试将 request 转换为 MultipartRequest 请求对象，转换成功后从其中获取 name 对应的文件列表并将对应文件对象保存到 arg 变量之中；若未获取到则会从 request 获取 name 对应 param 请求参数在其不为空时更新 arg 变量值，最后返回 arg 变量值。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Override@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);if (servletRequest != null) {Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {return mpArg;}}Object arg = null;MultipartRequest multipartRequest = request.getNativeRequest(MultipartRequest.class);if (multipartRequest != null) {List<MultipartFile> files = multipartRequest.getFiles(name);if (!files.isEmpty()) {arg = (files.size() == 1 ? files.get(0) : files);}}if (arg == null) {String[] paramValues = request.getParameterValues(name);if (paramValues != null) {arg = (paramValues.length == 1 ? paramValues[0] : paramValues);}}return arg;}
}4.2.5 handleMissingValue 方法
handleMissingValue 方法根据 request 参数的类型抛出不同的异常。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter, NativeWebRequest request)throws Exception {HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);if (MultipartResolutionDelegate.isMultipartArgument(parameter)) {if (servletRequest == null || !MultipartResolutionDelegate.isMultipartRequest(servletRequest)) {throw new MultipartException("Current request is not a multipart request");}else {throw new MissingServletRequestPartException(name);}}else {throw new MissingServletRequestParameterException(name,parameter.getNestedParameterType().getSimpleName());}}
}5 PathVariableMethodArgumentResolver 类
PathVariableMethodArgumentResolver 类用于路径参数的解析，由于其不存在拥有 ConfigurableBeanFactory 类型参数的构造方法，因此其参数名称及值不支持使用 ${...} 及 #{expression} 修饰来运行时解析。
5.1 常量
与 RequestParamMethodArgumentResolver 一样，PathVariableMethodArgumentResolver 类也有一个用于标识字符串类型描述符的 STRING_TYPE_DESCRIPTOR；
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {private static final TypeDescriptor STRING_TYPE_DESCRIPTOR = TypeDescriptor.valueOf(String.class);
}5.2 方法
5.2.1 supportsParameter 方法
supportsParameter 方法在参数没有使用 PathVariable 注解修饰时直接返回 false，在参数类型为 Map 时则会返回 PathVariable 注解对象是否有 value 参数值，参数为其他类型则直接返回 true。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overridepublic boolean supportsParameter(MethodParameter parameter) {if (!parameter.hasParameterAnnotation(PathVariable.class)) {return false;}if (Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {PathVariable pathVariable = parameter.getParameterAnnotation(PathVariable.class);return (pathVariable != null && StringUtils.hasText(pathVariable.value()));}return true;}
}5.2.2 createNamedValueInfo 方法
createNamedValueInfo 方法直接使用 PathVariable 注解对象创建 PathVariableNamedValueInfo 对象并返回。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {PathVariable ann = parameter.getParameterAnnotation(PathVariable.class);Assert.state(ann != null, "No PathVariable annotation");return new PathVariableNamedValueInfo(ann);}
}5.2.3 resolveName 方法
resolveName 方法从 request 所绑定的 HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE 属性中获取 name 对应值并返回。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Override@SuppressWarnings("unchecked")@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {Map<String, String> uriTemplateVars = (Map<String, String>) request.getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);return (uriTemplateVars != null ? uriTemplateVars.get(name) : null);}
}5.2.4 handleMissingValue 方法
handleMissingValue 方法直接抛出 MissingPathVariableException 异常。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletRequestBindingException {throw new MissingPathVariableException(name, parameter);}
}5.2.5 handleResolvedValue 方法
handleResolvedValue 方法将当前解析参数以 name 与 value 映射的方式保存到 request 请求的 PATH_VARIABLES 属性之中以供之后使用。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {@Override@SuppressWarnings("unchecked")protected void handleResolvedValue(@Nullable Object arg, String name, MethodParameter parameter,@Nullable ModelAndViewContainer mavContainer, NativeWebRequest request) {String key = View.PATH_VARIABLES;int scope = RequestAttributes.SCOPE_REQUEST;Map<String, Object> pathVars = (Map<String, Object>) request.getAttribute(key, scope);if (pathVars == null) {pathVars = new HashMap<>();request.setAttribute(key, pathVars, scope);}pathVars.put(name, arg);}
}5.3 PathVariableNamedValueInfo 内部类
PathVariableNamedValueInfo 内部类继承了 NamedValueInfo 方法扩展了使用 PathVariable 注解对象进行对象创建。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {private static class PathVariableNamedValueInfo extends NamedValueInfo {public PathVariableNamedValueInfo(PathVariable annotation) {super(annotation.name(), annotation.required(), ValueConstants.DEFAULT_NONE);}}
}6 RequestHeaderMethodArgumentResolver 类
RequestHeaderMethodArgumentResolver 类用于 RequestHeader 修饰的请求头参数的解析；
6.1 方法
6.1.1 构造方法
RequestHeaderMethodArgumentResolver 类实现了带 ConfigurableBeanFactory 类型参数的构造方法。
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {public RequestHeaderMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {super(beanFactory);}
}6.1.2 supportsParameter 方法
supportsParameter 方法直接返回当前属性是否不为 Map 对象且使用 RequestHeader 注解进行修饰；
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return (parameter.hasParameterAnnotation(RequestHeader.class) &&!Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType()));}
}6.1.3 createNamedValueInfo 方法
createNamedValueInfo 方法直接使用修饰参数的 RequestHeader 注解对象创建 RequestHeaderNamedValueInfo 对象并返回；
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {RequestHeader ann = parameter.getParameterAnnotation(RequestHeader.class);Assert.state(ann != null, "No RequestHeader annotation");return new RequestHeaderNamedValueInfo(ann);}
}6.1.4 resolveName 方法
resolveName 方法直接获取 request 对象对应请求值并返回；
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Override@Nullableprotected 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;}}
}6.1.5 handleMissingValue 方法
handleMissingValue 方法直接抛出 MissingRequestHeaderException 异常；
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletRequestBindingException {throw new MissingRequestHeaderException(name, parameter);}
}6.2 RequestHeaderNamedValueInfo 内部类
RequestHeaderNamedValueInfo 内部类继承了 NamedValueInfo 方法扩展了使用 RequestHeader 注解对象进行对象创建。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {private RequestHeaderNamedValueInfo(RequestHeader annotation) {super(annotation.name(), annotation.required(), annotation.defaultValue());}}
}7 MatrixVariableMethodArgumentResolver 类
MatrixVariableMethodArgumentResolver 类为 MatrixVariable 修饰的矩阵参数的的解析，由于其不存在拥有 ConfigurableBeanFactory 类型参数的构造方法，因此其参数名称及值也不支持使用 ${...} 及 #{expression} 修饰来运行时解析。
7.1 方法
7.1.1 构造方法
MatrixVariableMethodArgumentResolver 类只有一个无参构造方法，未设置 ConfigurableBeanFactory 对象工厂对象。
public class MatrixVariableMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {public MatrixVariableMethodArgumentResolver() {super(null);}
}7.1.2 supportsParameter 方法
supportsParameter 方法在参数为使用 MatrixVariable 参数修饰时直接返回 false，在参数为 Map 对象时，则会返回 MatrixVariable 对象的 value 是否有值，否则直接返回 true。
public class MatrixVariableMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {if (!parameter.hasParameterAnnotation(MatrixVariable.class)) {return false;}if (Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {MatrixVariable matrixVariable = parameter.getParameterAnnotation(MatrixVariable.class);return (matrixVariable != null && StringUtils.hasText(matrixVariable.name()));}return true;}
}7.1.3 createNamedValueInfo 方法
createNamedValueInfo 方法使用修饰参数的 MatrixVariable 对象创建 MatrixVariableNamedValueInfo 对象并返回。
public class MatrixVariableMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {MatrixVariable ann = parameter.getParameterAnnotation(MatrixVariable.class);Assert.state(ann != null, "No MatrixVariable annotation");return new MatrixVariableNamedValueInfo(ann);}
}7.1.4 resolveName 方法
resolveName 方法首先获取在 RequestMappingInfoHandlerMapping 对象的单 mapping 参数 handleMatch 方法扩展中绑定到 request 请求对象上的 HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE 属性映射值，在其为空时直接返回 null；随后在注解的 pathVar 不为 ValueConstants.DEFAULT_NONE 时，从绑定的映射值中获取对应值 Map 并将 name 对应值保存到 paramValues 变量之中，否则遍历所有映射值，将其中的 name 对应值保存至 paramValues 变量之中，注意该情况下，不同映射值不允许拥有多个 name 对应值，存在则会抛出 ServletRequestBindingException 异常；最后在 paramValues 为空时直接返回 null，在其只有一个元素则会返回第一个元素，否则返回 paramValues。
public class MatrixVariableMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Override@SuppressWarnings("unchecked")@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {Map<String, MultiValueMap<String, String>> pathParameters = (Map<String, MultiValueMap<String, String>>)request.getAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);if (CollectionUtils.isEmpty(pathParameters)) {return null;}MatrixVariable ann = parameter.getParameterAnnotation(MatrixVariable.class);Assert.state(ann != null, "No MatrixVariable annotation");String pathVar = ann.pathVar();List<String> paramValues = null;if (!pathVar.equals(ValueConstants.DEFAULT_NONE)) {if (pathParameters.containsKey(pathVar)) {paramValues = pathParameters.get(pathVar).get(name);}}else {boolean found = false;paramValues = new ArrayList<>();for (MultiValueMap<String, String> params : pathParameters.values()) {if (params.containsKey(name)) {if (found) {String paramType = parameter.getNestedParameterType().getName();throw new ServletRequestBindingException("Found more than one match for URI path parameter '" + name +"' for parameter type [" + paramType + "]. Use 'pathVar' attribute to disambiguate.");}paramValues.addAll(params.get(name));found = true;}}}if (CollectionUtils.isEmpty(paramValues)) {return null;}else if (paramValues.size() == 1) {return paramValues.get(0);}else {return paramValues;}}
}7.1.5 handleMissingValue 方法
handleMissingValue 方法直接抛出 MissingMatrixVariableException 异常。
public class MatrixVariableMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletRequestBindingException {throw new MissingMatrixVariableException(name, parameter);}
}7.2 MatrixVariableNamedValueInfo 内部类
MatrixVariableNamedValueInfo 内部类继承了 NamedValueInfo 方法扩展了使用 MatrixVariable 注解对象进行对象创建。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {private RequestHeaderNamedValueInfo(RequestHeader annotation) {super(annotation.name(), annotation.required(), annotation.defaultValue());}}
}8 RequestAttributeMethodArgumentResolver 类
RequestAttributeMethodArgumentResolver 类为 RequestAttribute 修饰的请求属性解析；
8.1 方法
8.1.1 supportsParameter 方法
supportsParameter 方法直接返回参数是否使用 RequestAttribute 注解修饰。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return parameter.hasParameterAnnotation(RequestAttribute.class);}
}8.1.2 createNamedValueInfo 方法
createNamedValueInfo 方法使用 RequestAttribute 对象的 name、required 及 alueConstants.DEFAULT_NONE 值创建 NamedValueInfo 对象并返回。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {RequestAttribute ann = parameter.getParameterAnnotation(RequestAttribute.class);Assert.state(ann != null, "No RequestAttribute annotation");return new NamedValueInfo(ann.name(), ann.required(), ValueConstants.DEFAULT_NONE);}
}8.1.3 resolveName 方法
resolveName 方法直接获取 request 中 name 对应属性值并返回。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Override@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request){return request.getAttribute(name, RequestAttributes.SCOPE_REQUEST);}
}8.1.4 handleMissingValue 方法
handleMissingValue 方法虽然同样也是抛出 ServletRequestBindingException 异常，但做出了对应适配。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletException {throw new ServletRequestBindingException("Missing request attribute '" + name +"' of type " + parameter.getNestedParameterType().getSimpleName());}
}9 SessionAttributeMethodArgumentResolver 类
SessionAttributeMethodArgumentResolver 类为 SessionAttribute 修饰的请求属性解析；其实现基本与 RequestAttributeMethodArgumentResolver 一致，唯一的差别来自获取属性的作用域，RequestAttributeMethodArgumentResolver 类获取的是单次请求绑定的属性，而 SessionAttributeMethodArgumentResolver 则可获取整个会话中的对应属性。
public class SessionAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return parameter.hasParameterAnnotation(SessionAttribute.class);}@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {SessionAttribute ann = parameter.getParameterAnnotation(SessionAttribute.class);Assert.state(ann != null, "No SessionAttribute annotation");return new NamedValueInfo(ann.name(), ann.required(), ValueConstants.DEFAULT_NONE);}@Override@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) {return request.getAttribute(name, RequestAttributes.SCOPE_SESSION);}@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletException {throw new ServletRequestBindingException("Missing session attribute '" + name +"' of type " + parameter.getNestedParameterType().getSimpleName());}}10 ExpressionValueMethodArgumentResolver 类
ExpressionValueMethodArgumentResolver 类实现的 Value 注解修饰的参数的解析，其值与单次请求无关，只与 Value 注解设置的 value 方法值有关。
10.1 方法
10.1.1 构造方法
ExpressionValueMethodArgumentResolver 的构造方法也是直接向父类提供 ConfigurableBeanFactory 对象工厂来进行对象创建。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {public ExpressionValueMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {super(beanFactory);}
}10.1.2 supportsParameter 方法
supportsParameter 方法直接返回 parameter 参数是否使用 Value 注解进行了修饰。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return parameter.hasParameterAnnotation(Value.class);}
}10.1.3 createNamedValueInfo 方法
createNamedValueInfo 方法直接使用 Value 对象创建 ExpressionValueNamedValueInfo 对象并返回。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {Value ann = parameter.getParameterAnnotation(Value.class);Assert.state(ann != null, "No Value annotation");return new ExpressionValueNamedValueInfo(ann);}
}10.1.4 resolveName 方法
由于 Value 修饰的参数值与请求无关，直接使用 Value 注解中定义的 value 值进行解析，因此此处直接返回 null，表明使用 ExpressionValueNamedValueInfo 对象的默认值进行解析。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Override@Nullableprotected Object resolveName(String name, MethodParameter parameter, NativeWebRequest webRequest) throws Exception {// No name to resolvereturn null;}
}10.1.5 handleMissingValue 方法
handleMissingValue 方法直接抛出 UnsupportedOperationException 异常。
public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected void handleMissingValue(String name, MethodParameter parameter) throws ServletException {throw new UnsupportedOperationException("@Value is never required: " + parameter.getMethod());}
}10.2 ExpressionValueNamedValueInfo 内部类
ExpressionValueNamedValueInfo 内部类继承了 NamedValueInfo 方法扩展了使用 Value 注解对象进行对象创建，其名称写死为 @Value，是否必填写死为 false，而默认值则使用 Value 对象的 value 方法配置值。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {private RequestHeaderNamedValueInfo(RequestHeader annotation) {super(annotation.name(), annotation.required(), annotation.defaultValue());}}
}11 ServletCookieValueMethodArgumentResolver 类
ServletCookieValueMethodArgumentResolver 类用于解析 CookieValue 注解修饰的参数。
11.1 AbstractCookieValueMethodArgumentResolver 抽象类
11.1.1 方法
构造方法
AbstractCookieValueMethodArgumentResolver 的构造方法也是直接向父类提供 ConfigurableBeanFactory 对象工厂来进行对象创建。
public abstract class AbstractCookieValueMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {public AbstractCookieValueMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {super(beanFactory);}
}supportsParameter 方法
supportsParameter 方法 parameter 参数是否使用 CookieValue 注解进行修饰。
public abstract class AbstractCookieValueMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overridepublic boolean supportsParameter(MethodParameter parameter) {return parameter.hasParameterAnnotation(CookieValue.class);}
}createNamedValueInfo 方法
createNamedValueInfo 方法直接使用 CookieValue 对象创建 CookieValueNamedValueInfo 对象并返回。
public abstract class AbstractCookieValueMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {CookieValue annotation = parameter.getParameterAnnotation(CookieValue.class);Assert.state(annotation != null, "No CookieValue annotation");return new CookieValueNamedValueInfo(annotation);}
}handleMissingValue 方法
handleMissingValue 方法直接抛出 MissingRequestCookieException 异常。
public abstract class AbstractCookieValueMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver {@Overrideprotected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {CookieValue annotation = parameter.getParameterAnnotation(CookieValue.class);Assert.state(annotation != null, "No CookieValue annotation");return new CookieValueNamedValueInfo(annotation);}
}CookieValueNamedValueInfo 内部类
CookieValueNamedValueInfo 内部类继承了 NamedValueInfo 方法扩展了使用 CookieValue 注解对象进行对象创建。
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolverimplements UriComponentsContributor {private static final class CookieValueNamedValueInfo extends NamedValueInfo {private CookieValueNamedValueInfo(CookieValue annotation) {super(annotation.name(), annotation.required(), annotation.defaultValue());}}
}11.2 属性
ServletCookieValueMethodArgumentResolver 类扩展了一个 urlPathHelper 路径解析辅助器属性。
public class ServletCookieValueMethodArgumentResolver extends AbstractCookieValueMethodArgumentResolver {private UrlPathHelper urlPathHelper = UrlPathHelper.defaultInstance;public void setUrlPathHelper(UrlPathHelper urlPathHelper) {this.urlPathHelper = urlPathHelper;}
}11.3 方法
11.3.1 构造方法
ServletCookieValueMethodArgumentResolver 的构造方法也是直接向父类提供 ConfigurableBeanFactory 对象工厂来进行对象创建。
public class ServletCookieValueMethodArgumentResolver extends AbstractCookieValueMethodArgumentResolver {public ServletCookieValueMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory) {super(beanFactory);}
}11.3.2 resolveName 方法
resolveName 方法将 webRequest 参数转换为 HttpServletRequest 对象之后尝试从中获取 cookieName 对应 cookie 值，在参数类型就是 Cookie 时直接返回该 Cookie 对象，否则再起不为空时利用 urlPathHelper 将 cookie 解码然后返回，否则返回 null。
public class ServletCookieValueMethodArgumentResolver extends AbstractCookieValueMethodArgumentResolver {@Override@Nullableprotected Object resolveName(String cookieName, MethodParameter parameter,NativeWebRequest webRequest) throws Exception {HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);Assert.state(servletRequest != null, "No HttpServletRequest");Cookie cookieValue = WebUtils.getCookie(servletRequest, cookieName);if (Cookie.class.isAssignableFrom(parameter.getNestedParameterType())) {return cookieValue;}else if (cookieValue != null) {return this.urlPathHelper.decodeRequestString(servletRequest, cookieValue.getValue());}else {return null;}}
}