SpringBoot 關(guān)于日期時(shí)間格式化處理方式總結(jié)

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來自：juejin.im/post/5e62817fe51d4526d05962a2

完成目標(biāo)

• 請(qǐng)求入?yún)?String（指定格式）轉(zhuǎn) Date，支持get、post（content-type=application/json）

• 返回?cái)?shù)據(jù)為Date類型轉(zhuǎn)為指定的日期時(shí)間格式字符創(chuàng)

• 支持Java8 日期 API，如：LocalTime、localDate 和 LocalDateTime

GET請(qǐng)求及POST表單日期時(shí)間字符串格式轉(zhuǎn)換

這種情況要和時(shí)間作為Json字符串時(shí)區(qū)別對(duì)待，因?yàn)榍岸薺son轉(zhuǎn)后端pojo底層使用的是Json序列化Jackson工具（HttpMessgeConverter）；而時(shí)間字符串作為普通請(qǐng)求參數(shù)傳入時(shí)，轉(zhuǎn)換用的是Converter，兩者在處理方式上是有區(qū)別。

@Configuration
public?class?DateConverterConfig?{
????@Bean
????public?Converter?localDateConverter()?{
???????return?new?Converter()?{
????????????@Override
????????????public?LocalDate?convert(String?source)?{
????????????????return?LocalDate.parse(source,?DateTimeFormatter.ofPattern("yyyy-MM-dd"));
????????????}
????????};
????}

????@Bean
????public?Converter?localDateTimeConverter()?{
????????return?new?Converter()?{
????????????@Override
????????????public?LocalDateTime?convert(String?source)?{
????????????????return?LocalDateTime.parse(source,?DateTimeFormatter.ofPattern("yyyy-MM-dd?HH:mm:ss"));
????????????}
????????};
????}
}

@Bean
@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")
public?Converter?localDateConverter()?{
????return?source?->?LocalDate.parse(source,?DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT));
}

Caused by: java.lang.IllegalArgumentException: Unable to determine source type  and target type  for your Converter [com.example.demo126.config.MappingConverterAdapter$$Lambda$522/817994751]; does the class parameterize those types?

adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());

@Override
public?void?addFormatters(FormatterRegistry?registry)?{
????for?(Converter?converter?:?getBeansOfType(Converter.class))?{
???????registry.addConverter(converter);
????}
????for?(GenericConverter?converter?:?getBeansOfType(GenericConverter.class))?{
???????registry.addConverter(converter);
????}
????for?(Formatter?formatter?:?getBeansOfType(Formatter.class))?{
???????registry.addFormatter(formatter);
????}
}

public?ResolvableType?as(Class?type)?{
????if?(this?==?NONE)?{
??????return?NONE;
????}
????Class?resolved?=?resolve();
????if?(resolved?==?null?||?resolved?==?type)?{
??????return?this;
????}
????for?(ResolvableType?interfaceType?:?getInterfaces())?{
??????ResolvableType?interfaceAsType?=?interfaceType.as(type);
??????if?(interfaceAsType?!=?NONE)?{
????????return?interfaceAsType;
??????}
????}
????return?getSuperType().as(type);
}

@Bean
@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")
public?Converter?localDateTimeConverter()?{
??return?source?->?LocalDateTime.parse(source,?DateTimeUtils.DEFAULT_FORMATTER);
}

@Component
public?class?DateConverter?implements?Converter<String,?Date>?{
????@Override
????public?Date?convert(String?value)?{
????????/**
?????????*?可對(duì)value進(jìn)行正則匹配，支持日期、時(shí)間等多種類型轉(zhuǎn)換
?????????*?這里我偷個(gè)懶，在匹配Date日期格式時(shí)直接使用了?hutool?為我們已經(jīng)寫好的解析工具類，這里就不重復(fù)造輪子了
?????????*?cn.hutool.core.date.DateUtil
?????????*?@param?value
?????????*?@return
?????????*/
????????return?DateUtil.parse(value.trim());
????}
}

<dependency>
??<groupId>cn.hutoolgroupId>
??<artifactId>hutool-allartifactId>
??<version>5.1.3version>
dependency>

@DateTimeFormat(pattern?=?"yyyy-MM-dd")
private?Date?startDate;

@ControllerAdvice
public?class?GlobalExceptionHandler?{

????@InitBinder
????protected?void?initBinder(WebDataBinder?binder)?{
????????binder.registerCustomEditor(LocalDate.class,?new?PropertyEditorSupport()?{
????????????@Override
????????????public?void?setAsText(String?text)?throws?IllegalArgumentException?{
????????????????setValue(LocalDate.parse(text,?DateTimeFormatter.ofPattern("yyyy-MM-dd")));
????????????}
????????});
????????binder.registerCustomEditor(LocalDateTime.class,?new?PropertyEditorSupport()?{
????????????@Override
????????????public?void?setAsText(String?text)?throws?IllegalArgumentException?{
????????????????setValue(LocalDateTime.parse(text,?DateTimeFormatter.ofPattern("yyyy-MM-dd?HH:mm:ss")));
????????????}
????????});
????????binder.registerCustomEditor(LocalTime.class,?new?PropertyEditorSupport()?{
????????????@Override
????????????public?void?setAsText(String?text)?throws?IllegalArgumentException?{
????????????????setValue(LocalTime.parse(text,?DateTimeFormatter.ofPattern("HH:mm:ss")));
????????????}
????????});
????}
}

JSON入?yún)⒓胺祷刂等痔幚?/h2>

請(qǐng)求類型為:post,content-type=application/json， 后臺(tái)用@RequestBody接收，默認(rèn)接收及返回值格式為:yyyy-MM-dd HH:mm:ss

修改 application.yml 文件

在application.propertities文件中增加如下內(nèi)容：

spring:
	jackson:
		date-format: yyyy-MM-dd HH:mm:ss
		time-zone: GMT+8

• 支持（content-type=application/json）請(qǐng)求中格式為 yyyy-MM-dd HH:mm:ss的字符串，后臺(tái)用@RequestBody接收，及返回值date轉(zhuǎn)為yyyy-MM-dd HH:mm:ss格式string；

• 不支持（content-type=application/json）請(qǐng)求中yyyy-MM-dd等類型的字符串轉(zhuǎn)為date；

• 不支持java8日期api;

利用Jackson的JSON序列化和反序列化

@Configuration
public?class?JacksonConfig?{

????/**?默認(rèn)日期時(shí)間格式?*/
????public?static?final?String?DEFAULT_DATE_TIME_FORMAT?=?"yyyy-MM-dd?HH:mm:ss";
????/**?默認(rèn)日期格式?*/
????public?static?final?String?DEFAULT_DATE_FORMAT?=?"yyyy-MM-dd";
????/**?默認(rèn)時(shí)間格式?*/
????public?static?final?String?DEFAULT_TIME_FORMAT?=?"HH:mm:ss";

????@Bean
????public?MappingJackson2HttpMessageConverter?mappingJackson2HttpMessageConverter()?{
????????MappingJackson2HttpMessageConverter?converter?=?new?MappingJackson2HttpMessageConverter();
????????ObjectMapper?objectMapper?=?new?ObjectMapper();

????????//?忽略json字符串中不識(shí)別的屬性
????????objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,?false);
????????//?忽略無法轉(zhuǎn)換的對(duì)象?
????????objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS,?false);
????????//?PrettyPrinter?格式化輸出
????????objectMapper.configure(SerializationFeature.INDENT_OUTPUT,?true);
????????//?NULL不參與序列化
????????objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

????????//?指定時(shí)區(qū)
????????objectMapper.setTimeZone(TimeZone.getTimeZone("GMT+8:00"));
????????//?日期類型字符串處理
????????objectMapper.setDateFormat(new?SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT));

????????//?java8日期日期處理
????????JavaTimeModule?javaTimeModule?=?new?JavaTimeModule();
????????javaTimeModule.addSerializer(LocalDateTime.class,?new?LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
????????javaTimeModule.addSerializer(LocalDate.class,?new?LocalDateSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)));
????????javaTimeModule.addSerializer(LocalTime.class,?new?LocalTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));
????????javaTimeModule.addDeserializer(LocalDateTime.class,?new?LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
????????javaTimeModule.addDeserializer(LocalDate.class,?new?LocalDateDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)));
????????javaTimeModule.addDeserializer(LocalTime.class,?new?LocalTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));
????????objectMapper.registerModule(javaTimeModule);

????????converter.setObjectMapper(objectMapper);
????????return?converter;
????}
}

總結(jié)：

• 支持（content-type=application/json）請(qǐng)求中格式為yyyy-MM-dd HH:mm:ss的字符串，后臺(tái)用@RequestBody接收，及返回值Date轉(zhuǎn)為yyyy-MM-dd HH:mm:ss格式String；

• 支持java8日期api；

• 不支持（content-type=application/json）請(qǐng)求中yyyy-MM-dd等類型的字符串轉(zhuǎn)為Date；

以上兩種方式為JSON入?yún)⒌娜只幚恚扑]使用方式二，尤其適合大型項(xiàng)目在基礎(chǔ)包中全局設(shè)置。

JSON入?yún)⒓胺祷刂稻植坎町惢幚?/h2>

場(chǎng)景：假如全局日期時(shí)間處理格式為：yyyy-MM-dd HH:mm:ss，但是某個(gè)字段要求接收或返回日期yyyy-MM-dd。

方式一 使用springboot自帶的注解@JsonFormat(pattern = "yyyy-MM-dd")，如下所示：

@JsonFormat(pattern?=?"yyyy-MM-dd",?timezone="GMT+8")
private?Date?releaseDate;

點(diǎn)評(píng)：springboot默認(rèn)提供，功能強(qiáng)大，滿足常見場(chǎng)景使用，并可指定時(shí)區(qū)。

方式二

自定義日期序列化與反序列化，如下所示：

/**
?*?日期序列化
?*/
public?class?DateJsonSerializer?extends?JsonSerializer<Date>?{
????@Override
????public?void?serialize(Date?date,?JsonGenerator?jsonGenerator,?SerializerProvider?serializerProvider)?throws?IOException?{
????????SimpleDateFormat?dateFormat?=?new?SimpleDateFormat("yyyy-MM-dd");
????????jsonGenerator.writeString(dateFormat.format(date));
????}
}

/**
?*?日期反序列化
?*/
public?class?DateJsonDeserializer?extends?JsonDeserializer<Date>?{
????@Override
????public?Date?deserialize(JsonParser?jsonParser,?DeserializationContext?deserializationContext)?throws?IOException?{
????????try?{
????????????SimpleDateFormat?dateFormat?=?new?SimpleDateFormat("yyyy-MM-dd");
????????????return?dateFormat.parse(jsonParser.getText());
????????}?catch?(ParseException?e)?{
????????????throw?new?RuntimeException(e);
????????}
????}
}

/**
?*?使用方式
?*/
@JsonSerialize(using?=?DateJsonSerializer.class)
@JsonDeserialize(using?=?DateJsonDeserializer.class)
private?Date?releaseDate;
復(fù)制代碼日期時(shí)間格式化處理方式完整配置
@Configuration
public?class?DateHandlerConfig?{

????/**?默認(rèn)日期時(shí)間格式?*/
????public?static?final?String?DEFAULT_DATE_TIME_FORMAT?=?"yyyy-MM-dd?HH:mm:ss";
????/**?默認(rèn)日期格式?*/
????public?static?final?String?DEFAULT_DATE_FORMAT?=?"yyyy-MM-dd";
????/**?默認(rèn)時(shí)間格式?*/
????public?static?final?String?DEFAULT_TIME_FORMAT?=?"HH:mm:ss";

????/**
?????*?LocalDate轉(zhuǎn)換器，用于轉(zhuǎn)換RequestParam和PathVariable參數(shù)
?????*?`@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")`:?等requestMappingHandlerAdapter?bean注冊(cè)完成之后
?????*?再添加自己的`converter`就不會(huì)注冊(cè)到`FormattingConversionService`中
?????*/
????@Bean
????@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")
????public?Converter?localDateConverter()?{
????????return?source?->?LocalDate.parse(source,?DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT));
????}

????/**
?????*?LocalDateTime轉(zhuǎn)換器，用于轉(zhuǎn)換RequestParam和PathVariable參數(shù)
?????*/
????@Bean
????@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")
????public?Converter?localDateTimeConverter()?{
????????return?source?->?LocalDateTime.parse(source,?DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT));
????}

????/**
?????*?LocalTime轉(zhuǎn)換器，用于轉(zhuǎn)換RequestParam和PathVariable參數(shù)
?????*/
????@Bean
????@ConditionalOnBean(name?=?"requestMappingHandlerAdapter")
????public?Converter?localTimeConverter()?{
????????return?source?->?LocalTime.parse(source,?DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT));
????}

????/**
?????*?Date轉(zhuǎn)換器，用于轉(zhuǎn)換RequestParam和PathVariable參數(shù)
?????*?這里關(guān)于解析各種格式的日期格式采用了?hutool?的日期解析工具類
?????*/
????@Bean
????public?Converter?dateConverter()?{
????????return?new?Converter()?{
????????????@Override
????????????public?Date?convert(String?source)?{
????????????????return?DateUtil.parse(source.trim());
????????????}
????????};
????}

????/**
?????*?Json序列化和反序列化轉(zhuǎn)換器，用于轉(zhuǎn)換Post請(qǐng)求體中的json以及將我們的對(duì)象序列化為返回響應(yīng)的json
?????*/
????@Bean
????public?ObjectMapper?objectMapper(){
????????ObjectMapper?objectMapper?=?new?ObjectMapper();
????????objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
????????objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);

????????//LocalDateTime系列序列化和反序列化模塊，繼承自jsr310，我們?cè)谶@里修改了日期格式
????????JavaTimeModule?javaTimeModule?=?new?JavaTimeModule();
????????javaTimeModule.addSerializer(LocalDateTime.class,new?LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
????????javaTimeModule.addSerializer(LocalDate.class,new?LocalDateSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)));
????????javaTimeModule.addSerializer(LocalTime.class,new?LocalTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));
????????javaTimeModule.addDeserializer(LocalDateTime.class,new?LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
????????javaTimeModule.addDeserializer(LocalDate.class,new?LocalDateDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)));
????????javaTimeModule.addDeserializer(LocalTime.class,new?LocalTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));


????????//Date序列化和反序列化
????????javaTimeModule.addSerializer(Date.class,?new?JsonSerializer<>()?{
????????????@Override
????????????public?void?serialize(Date?date,?JsonGenerator?jsonGenerator,?SerializerProvider?serializerProvider)?throws?IOException?{
????????????????SimpleDateFormat?formatter?=?new?SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT);
????????????????String?formattedDate?=?formatter.format(date);
????????????????jsonGenerator.writeString(formattedDate);
????????????}
????????});
????????javaTimeModule.addDeserializer(Date.class,?new?JsonDeserializer<>()?{
????????????@Override
????????????public?Date?deserialize(JsonParser?jsonParser,?DeserializationContext?deserializationContext)?throws?IOException,?JsonProcessingException?{
????????????????SimpleDateFormat?format?=?new?SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT);
????????????????String?date?=?jsonParser.getText();
????????????????try?{
????????????????????return?format.parse(date);
????????????????}?catch?(ParseException?e)?{
????????????????????throw?new?RuntimeException(e);
????????????????}
????????????}
????????});

????????objectMapper.registerModule(javaTimeModule);
????????return?objectMapper;
????}
}

接下來進(jìn)入debug模式，看看mvc是如何將我們r(jià)equest中的參數(shù)綁定到我們controller層方法入?yún)⒌模?/section>

寫一個(gè)簡(jiǎn)單controller，打個(gè)斷點(diǎn)看看方法調(diào)用棧：

@GetMapping("/getDate")
public?LocalDateTime?getDate(@RequestParam?LocalDate?date,
?????????????????????????????@RequestParam?LocalDateTime?dateTime,
?????????????????????????????@RequestParam?Date?originalDate)?{
????System.out.println(date);
????System.out.println(dateTime);
????System.out.println(originalDate);
????return?LocalDateTime.now();
}

調(diào)用接口以后，我們看下方法調(diào)用棧中一些關(guān)鍵方法：

//進(jìn)入DispatcherServlet
doService:942,?DispatcherServlet
//處理請(qǐng)求
doDispatch:1038,?DispatcherServlet
//生成調(diào)用鏈（前處理、實(shí)際調(diào)用方法、后處理）
handle:87,?AbstractHandlerMethodAdapter
//反射獲取到實(shí)際調(diào)用方法，準(zhǔn)備開始調(diào)用
invokeHandlerMethod:895,?RequestMappingHandlerAdapter
invokeAndHandle:102,?ServletInvocableHandlerMethod
//這里是關(guān)鍵，參數(shù)從這里開始獲取到
invokeForRequest:142,?InvocableHandlerMethod
doInvoke:215,?InvocableHandlerMethod
//這個(gè)是Java?reflect調(diào)用，因此一定是在這之前獲取到的參數(shù)
invoke:566,?Method

根據(jù)上述分析，發(fā)現(xiàn)invokeForRequest:142, InvocableHandlerMethod這里的代碼是用來拿到實(shí)際參數(shù)的：

@Nullable
public?Object?invokeForRequest(NativeWebRequest?request,?@Nullable?ModelAndViewContainer?mavContainer,
????????Object...?providedArgs)?throws?Exception?{
????//這個(gè)方法是獲取參數(shù)的，在這里下個(gè)斷
????Object[]?args?=?getMethodArgumentValues(request,?mavContainer,?providedArgs);
????if?(logger.isTraceEnabled())?{
????????logger.trace("Arguments:?"?+?Arrays.toString(args));
????}
????//這里開始調(diào)用方法
????return?doInvoke(args);
}

進(jìn)入這個(gè)方法看看是什么操作：

protected?Object[]?getMethodArgumentValues(NativeWebRequest?request,?@Nullable?ModelAndViewContainer?mavContainer,?Object...?providedArgs)?throws?Exception?{
????//獲取方法參數(shù)數(shù)組，包含了入?yún)⑿畔ⅲ热珙愋汀⒎盒偷鹊?/span>
????MethodParameter[]?parameters?=?getMethodParameters();
????//這個(gè)用來存放一會(huì)從request?parameter轉(zhuǎn)換的參數(shù)
????Object[]?args?=?new?Object[parameters.length];
????for?(int?i?=?0;?i???????MethodParameter?parameter?=?parameters[i];
??????parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
??????//這里看起來沒啥卵用（providedArgs為空）
??????args[i]?=?resolveProvidedArgument(parameter,?providedArgs);
??????//這里開始獲取到方法實(shí)際調(diào)用的參數(shù)，步進(jìn)
??????if?(this.argumentResolvers.supportsParameter(parameter))?{
????????//從名字就看出來：參數(shù)解析器解析參數(shù)
????????args[i]?=?this.argumentResolvers.resolveArgument(parameter,?mavContainer,?request,?this.dataBinderFactory);
????????continue;
??????}
????}
????return?args;
}

進(jìn)入resolveArgument看看：

public?Object?resolveArgument(MethodParameter?parameter,?@Nullable?ModelAndViewContainer?mavContainer,
??????????????????????????????NativeWebRequest?webRequest,?@Nullable?WebDataBinderFactory?binderFactory)?throws?Exception?{
??//根據(jù)方法入?yún)ⅲ@取對(duì)應(yīng)的解析器
??HandlerMethodArgumentResolver?resolver?=?getArgumentResolver(parameter);
??//開始解析參數(shù)（把請(qǐng)求中的parameter轉(zhuǎn)為方法的入?yún)ⅲ?/span>
??return?resolver.resolveArgument(parameter,?mavContainer,?webRequest,?binderFactory);
}
復(fù)制代碼這里根據(jù)參數(shù)獲取相應(yīng)的參數(shù)解析器，看看內(nèi)部如何獲取的：
//遍歷，調(diào)用supportParameter方法，跟進(jìn)看看
for?(HandlerMethodArgumentResolver?methodArgumentResolver?:?this.argumentResolvers)?{
??if?(methodArgumentResolver.supportsParameter(parameter))?{
????result?=?methodArgumentResolver;
????this.argumentResolverCache.put(parameter,?result);
????break;
??}
}

這里，遍歷參數(shù)解析器，查找有沒有適合的解析器！那么，有哪些參數(shù)解析器呢(我測(cè)試的時(shí)候有26個(gè))？？？我列出幾個(gè)重要的看看，是不是很眼熟！！！

{RequestParamMethodArgumentResolver@7686}
{PathVariableMethodArgumentResolver@8359}
{RequestResponseBodyMethodProcessor@8366}
{RequestPartMethodArgumentResolver@8367}

我們進(jìn)入最常用的一個(gè)解析器看看他的supportsParameter方法，發(fā)現(xiàn)就是通過參數(shù)注解來獲取相應(yīng)的解析器的。

public?boolean?supportsParameter(MethodParameter?parameter)?{
????//如果參數(shù)擁有注解@RequestParam，則走這個(gè)分支（知道為什么上文要對(duì)RequestParam和Json兩種數(shù)據(jù)區(qū)別對(duì)待了把）
????if?(parameter.hasParameterAnnotation(RequestParam.class))?{
????????//這個(gè)似乎是對(duì)Optional類型的參數(shù)進(jìn)行處理的
????????if?(Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType()))?{
????????????RequestParam?requestParam?=?parameter.getParameterAnnotation(RequestParam.class);
????????????return?(requestParam?!=?null?&&?StringUtils.hasText(requestParam.name()));
????????}
????????else?{
????????????return?true;
????????}
????}
????//......
}

也就是說，對(duì)于@RequestParam和@RequestBody以及@PathVariable注解的參數(shù)，SpringMVC會(huì)使用不同的參數(shù)解析器進(jìn)行數(shù)據(jù)綁定！

那么，這三種解析器分別使用什么Converter解析參數(shù)呢？我們分別進(jìn)入三種解析器看一看：

首先看下RequestParamMethodArgumentResolver發(fā)現(xiàn)內(nèi)部使用WebDataBinder進(jìn)行數(shù)據(jù)綁定，底層使用的是ConversionService （也就是我們的Converter注入的地方）

WebDataBinder?binder?=?binderFactory.createBinder(webRequest,?null,?namedValueInfo.name);
//通過DataBinder進(jìn)行數(shù)據(jù)綁定的
arg?=?binder.convertIfNecessary(arg,?parameter.getParameterType(),?parameter);

//跟進(jìn)convertIfNecessary()
public??T?convertIfNecessary(@Nullable?Object?value,?@Nullable?Class?requiredType,
????????????????????????????????@Nullable?MethodParameter?methodParam)?throws?TypeMismatchException?{

??return?getTypeConverter().convertIfNecessary(value,?requiredType,?methodParam);
}

//繼續(xù)跟進(jìn)，看到了把
ConversionService?conversionService?=?this.propertyEditorRegistry.getConversionService();
if?(editor?==?null?&&?conversionService?!=?null?&&?newValue?!=?null?&&?typeDescriptor?!=?null)?{
??TypeDescriptor?sourceTypeDesc?=?TypeDescriptor.forObject(newValue);
??if?(conversionService.canConvert(sourceTypeDesc,?typeDescriptor))?{
????try?{
??????return?(T)?conversionService.convert(newValue,?sourceTypeDesc,?typeDescriptor);
????}
????catch?(ConversionFailedException?ex)?{
??????//?fallback?to?default?conversion?logic?below
??????conversionAttemptEx?=?ex;
????}
??}
}

然后看下RequestResponseBodyMethodProcessor發(fā)現(xiàn)使用的轉(zhuǎn)換器是HttpMessageConverter類型的：

//resolveArgument方法內(nèi)部調(diào)用下面進(jìn)行參數(shù)解析
Object?arg?=?readWithMessageConverters(webRequest,?parameter,?parameter.getNestedGenericParameterType());

//step?into?readWithMessageConverters()，我們看到這里的Converter是HttpMessageConverter
for?(HttpMessageConverter?converter?:?this.messageConverters)?{
??Class>?converterType?=?(Class>)?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)?converter).read(targetClass,?msgToUse));
??????body?=?getAdvice().afterBodyRead(body,?msgToUse,?parameter,?targetType,?converterType);
????}
????else?{
??????body?=?getAdvice().handleEmptyBody(null,?message,?parameter,?targetType,?converterType);
????}
????break;
??}
}

最后看下PathVariableMethodArgumentResolver發(fā)現(xiàn) 和RequestParam走的執(zhí)行路徑一致（二者都是繼承自AbstractNamedValueMethodArgumentResolver解析器），因此代碼就不貼了。

總結(jié)

如果要轉(zhuǎn)換request傳來的參數(shù)到我們指定的類型，根據(jù)入?yún)⒆⒔庖M(jìn)行區(qū)分：

如果是RequestBody，那么通過配置ObjectMapper（這個(gè)玩意兒會(huì)注入到Jackson的HttpMessagConverter里面，即MappingJackson2HttpMessageConverter中）來實(shí)現(xiàn)Json格式數(shù)據(jù)的序列化和反序列化；如果是RequestParam或者PathVariable類型的參數(shù)，通過配置Converter實(shí)現(xiàn)參數(shù)轉(zhuǎn)換（這些Converter會(huì)注入到ConversionService中）。

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