作者：TinyThing
链接：https://www.jianshu.com/p/b52db905f020
0x0 背景
我的项目中应用LocalDateTime系列作为dto中工夫的类型，然而spring收到参数后总报错，为了全局配置工夫类型转换，尝试了如下3中办法。
注：本文基于Springboot2.0测试，如果无奈失效可能是spring版本较低导致的。PS：如果你的Controller中的LocalDate类型的参数啥注解（RequestParam、PathVariable等）都没加，也是会出错的，因为默认状况下，解析这种参数应用
ModelAttributeMethodProcessor进行解决，而这个处理器要通过反射实例化一个对象进去，而后再对对象中的各个参数进行convert，然而LocalDate类没有构造函数，无奈反射实例化因而会报错！！！
0x1 当LocalDateTime作为RequestParam或者PathVariable时
这种状况要和工夫作为Json字符串时区别对待，因为前端json转后端pojo底层应用的是Json序列化Jackson工具（HttpMessgeConverter）；而工夫字符串作为一般申请参数传入时，转换用的是Converter，两者有区别哦。
在这种状况下，有如下几种计划：
举荐一个开源收费的 Spring Boot 实战我的项目：
https://github.com/javastacks/spring-boot-best-practice
1. 应用Converter
import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.core.convert.converter.Converter;import org.springframework.http.converter.HttpMessageConverter;import java.time.LocalDate;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;@Configurationpublic class DateConfig { @Bean public Converter<String, LocalDate> localDateConverter() { return new Converter<>() { @Override public LocalDate convert(String source) { return LocalDate.parse(source, DateTimeFormatter.ofPattern("yyyy-MM-dd")); } }; } @Bean public Converter<String, LocalDateTime> localDateTimeConverter() { return new Converter<>() { @Override public LocalDateTime convert(String source) { return LocalDateTime.parse(source, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")); } }; }}以上两个bean会注入到spring mvc的参数解析器（如同叫做ParameterConversionService），当传入的字符串要转为LocalDateTime类时，spring会调用该Converter对这个入参进行转换。
2. 应用ControllerAdvice配合initBinder
@ControllerAdvicepublic 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"))); } }); }}从名字就可以看进去，这是在controller做环切（这外面还能够全局异样捕捉），在参数进入handler之前进行转换；转换为咱们相应的对象。
0x2 当LocalDateTime作为Json模式传入
这种状况下，如同上文形容，要利用Jackson的json序列化和反序列化来做：
@Configurationpublic class JacksonConfig { /** 默认日期工夫格局 */ public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss"; /** 默认日期格局 */ public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd"; /** 默认工夫格局 */ public static final String DEFAULT_TIME_FORMAT = "HH:mm:ss"; @Bean public ObjectMapper objectMapper(){ ObjectMapper objectMapper = new ObjectMapper();// objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);// objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE); 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).registerModule(new ParameterNamesModule()); return objectMapper; }}0x3 来个残缺的配置吧
Spring Boot 根底就不介绍了，举荐看这个实战我的项目：
https://github.com/javastacks/spring-boot-best-practice
package com.fly.hi.common.config;import com.fasterxml.jackson.core.JsonGenerator;import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.*;import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateDeserializer;import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateTimeDeserializer;import com.fasterxml.jackson.datatype.jsr310.deser.LocalTimeDeserializer;import com.fasterxml.jackson.datatype.jsr310.ser.LocalDateSerializer;import com.fasterxml.jackson.datatype.jsr310.ser.LocalDateTimeSerializer;import com.fasterxml.jackson.datatype.jsr310.ser.LocalTimeSerializer;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.core.convert.converter.Converter;import java.io.IOException;import java.text.ParseException;import java.text.SimpleDateFormat;import java.time.LocalDate;import java.time.LocalDateTime;import java.time.LocalTime;import java.time.format.DateTimeFormatter;import java.util.Date;@Configurationpublic class DateConfig { /** 默认日期工夫格局 */ public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss"; /** 默认日期格局 */ public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd"; /** 默认工夫格局 */ public static final String DEFAULT_TIME_FORMAT = "HH:mm:ss"; /** * LocalDate转换器，用于转换RequestParam和PathVariable参数 */ @Bean public Converter<String, LocalDate> localDateConverter() { return new Converter<>() { @Override public LocalDate convert(String source) { return LocalDate.parse(source, DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)); } }; } /** * LocalDateTime转换器，用于转换RequestParam和PathVariable参数 */ @Bean public Converter<String, LocalDateTime> localDateTimeConverter() { return new Converter<>() { @Override public LocalDateTime convert(String source) { return LocalDateTime.parse(source, DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)); } }; } /** * LocalTime转换器，用于转换RequestParam和PathVariable参数 */ @Bean public Converter<String, LocalTime> localTimeConverter() { return new Converter<>() { @Override public LocalTime convert(String source) { return LocalTime.parse(source, DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)); } }; } /** * Date转换器，用于转换RequestParam和PathVariable参数 */ @Bean public Converter<String, Date> dateConverter() { return new Converter<>() { @Override public Date convert(String source) { SimpleDateFormat format = new SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT); try { return format.parse(source); } catch (ParseException e) { throw new RuntimeException(e); } } }; } /** * Json序列化和反序列化转换器，用于转换Post申请体中的json以及将咱们的对象序列化为返回响应的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块，继承自jsr310，咱们在这里批改了日期格局 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; }}0x4 深入研究SpringMVC数据绑定过程
接下来进入debug模式，看看mvc是如何将咱们request中的参数绑定到咱们controller层办法入参的：
写一个简略controller，下个断点看看办法调用栈：
@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();}断住当前，咱们看下办法调用栈中一些要害办法：
//进入DispatcherServletdoService:942, DispatcherServlet//解决申请doDispatch:1038, DispatcherServlet//生成调用链（前解决、理论调用办法、后处理）handle:87, AbstractHandlerMethodAdapter//反射获取到理论调用办法，筹备开始调用invokeHandlerMethod:895, RequestMappingHandlerAdapterinvokeAndHandle:102, ServletInvocableHandlerMethod//这里是要害，参数从这里开始获取到invokeForRequest:142, InvocableHandlerMethoddoInvoke:215, InvocableHandlerMethod//这个是Java reflect调用，因而肯定是在这之前获取到的参数invoke:566, Method根据上述剖析，发现invokeForRequest:142, InvocableHandlerMethod这里的代码是用来拿到理论参数的：
@Nullablepublic Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { //这个办法是获取参数的，在这里下个断 Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs); if (logger.isTraceEnabled()) { logger.trace("Arguments: " + Arrays.toString(args)); } //这里开始调用办法 return doInvoke(args);}进入这个办法看看是什么操作：
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { //获取办法参数数组，蕴含了入参信息，比方类型、泛型等等 MethodParameter[] parameters = getMethodParameters(); //这个用来寄存一会从request parameter转换的参数 Object[] args = new Object[parameters.length]; for (int i = 0; i < parameters.length; i++) { MethodParameter parameter = parameters[i]; parameter.initParameterNameDiscovery(this.parameterNameDiscoverer); //这里看起来没啥卵用（providedArgs为空） args[i] = resolveProvidedArgument(parameter, providedArgs); //这里开始获取到办法理论调用的参数，步进 if (this.argumentResolvers.supportsParameter(parameter)) { //从名字就看进去：参数解析器解析参数 args[i] = this.argumentResolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory); continue; } } return args;}进入resolveArgument看看：
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception { //依据办法入参，获取对应的解析器 HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter); //开始解析参数（把申请中的parameter转为办法的入参） return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);}这里依据参数获取相应的参数解析器，看看外部如何获取的：
//遍历，调用supportParameter办法，跟进看看for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) { if (methodArgumentResolver.supportsParameter(parameter)) { result = methodArgumentResolver; this.argumentResolverCache.put(parameter, result); break; }}这里，遍历参数解析器，查找有没有适宜的解析器！那么，有哪些参数解析器呢(我测试的时候有26个)？？？我列出几个重要的看看，是不是很眼生！！！
{RequestParamMethodArgumentResolver@7686} {PathVariableMethodArgumentResolver@8359} {RequestResponseBodyMethodProcessor@8366} {RequestPartMethodArgumentResolver@8367} 咱们进入最罕用的一个解析器看看他的supportsParameter办法，发现就是通过参数注解来获取相应的解析器的。
public boolean supportsParameter(MethodParameter parameter) { //如果参数领有注解@RequestParam，则走这个分支（晓得为什么上文要对RequestParam和Json两种数据区别对待了把） if (parameter.hasParameterAnnotation(RequestParam.class)) { //这个仿佛是对Optional类型的参数进行解决的 if (Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) { RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class); return (requestParam != null && StringUtils.hasText(requestParam.name())); } else { return true; } } //......}也就是说，对于@RequestParam和@RequestBody以及@PathVariable注解的参数，SpringMVC会应用不通的参数解析器进行数据绑定！
那么，这三种解析器别离应用什么Converter解析参数呢？咱们别离进入三种解析器看一看：
首先看下RequestParamMethodArgumentResolver发现外部应用WebDataBinder进行数据绑定，底层应用的是ConversionService （也就是咱们的Converter注入的中央）
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);//通过DataBinder进行数据绑定的arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);//跟进convertIfNecessary()public <T> T convertIfNecessary(@Nullable Object value, @Nullable Class<T> requiredType, @Nullable MethodParameter methodParam) throws TypeMismatchException { return getTypeConverter().convertIfNecessary(value, requiredType, methodParam);}//持续跟进，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; } }}而后看下RequestResponseBodyMethodProcessor发现应用的转换器是HttpMessageConverter类型的：
//resolveArgument办法外部调用上面进行参数解析Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());//step into readWithMessageConverters()，咱们看到这里的Converter是HttpMessageConverterfor (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; }}最初看下PathVariableMethodArgumentResolver发现 和RequestParam走的执行门路统一（二者都是继承自AbstractNamedValueMethodArgumentResolver解析器），因而代码就不贴了。
0xFF总结
如果要转换request传来的参数到咱们指定的类型，依据入参注解要进行辨别：
- 如果是RequestBody，那么通过配置ObjectMapper（这个玩意儿会注入到Jackson的HttpMessagConverter外面，即
MappingJackson2HttpMessageConverter中）来实现Json格局数据的序列化和反序列化；- 如果是RequestParam或者PathVariable类型的参数，通过配置Converter实现参数转换（这些Converter会注入到ConversionService中）。
近期热文举荐：
1.1,000+ 道 Java面试题及答案整顿(2022最新版)
2.劲爆！Java 协程要来了。。。
3.Spring Boot 2.x 教程，太全了！
4.别再写满屏的爆爆爆炸类了，试试装璜器模式，这才是优雅的形式！！
5.《Java开发手册（嵩山版）》最新公布，速速下载！
感觉不错，别忘了顺手点赞+转发哦！