SpringBoot如何對LocalDateTime進行格式化並解析
【1】格式化後臺傳給前端的日期
首先第一點需要知道的是springboot默認依賴的json框架是jackson。
當使用@ResponseBody註解返回json格式數據時就是該框架在起作用。
SpringBoot對Date/DateTime配置
如果字段屬性是Date而非LocalDateTime時，通常我們會在application.properties裡面配置如下：
spring.mvc.date-format=yyyy-MM-dd HH:mm:ss spring.jackson.date-format=yyyy-MM-dd HH:mm:ss spring.jackson.time-zone=GMT+8 spring.jackson.serialization.write-dates-as-timestamps=false
如下圖所示，spring.jackson開頭的配置會被JacksonProperties類獲取進行使用。
當返回json格式的時候，Jackson就會根據配置文件中日期格式化的配置對結果進行處理。
但是如果字段屬性為LocalDateTime呢？這種配置就失去瞭作用。
第一種方式：配置localDateTimeSerializer
這時候建議配置如下：
/**
* Created by jianggc at 2020/7/1.
*/
@Configuration
public class LocalDateTimeSerializerConfig {
@Value("${spring.jackson.date-format:yyyy-MM-dd HH:mm:ss}")
private String pattern;
// localDateTime 序列化器
@Bean
public LocalDateTimeSerializer localDateTimeSerializer() {
return new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(pattern));
}
// localDateTime 反序列化器
@Bean
public LocalDateTimeDeserializer localDateTimeDeserializer() {
return new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(pattern));
}
@Bean
public Jackson2ObjectMapperBuilderCustomizer jackson2ObjectMapperBuilderCustomizer() {
// return new Jackson2ObjectMapperBuilderCustomizer() {
// @Override
// public void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder) {
jacksonObjectMapperBuilder.featuresToDisable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
// jacksonObjectMapperBuilder.serializerByType(LocalDateTime.class, localDateTimeSerializer());
// jacksonObjectMapperBuilder.deserializerByType(LocalDateTime.class,localDateTimeDeserializer());
// }
// };
//這種方式同上
return builder -> {
builder.serializerByType(LocalDateTime.class, localDateTimeSerializer());
builder.deserializerByType(LocalDateTime.class,localDateTimeDeserializer());
builder.simpleDateFormat(pattern);
};
}
}
第二種方式：@JsonFormat
這種配置方式自然是全局的，如果想針對某個字段特殊處理，可以在類字段上面添加註解@JsonFormat：
@JsonFormat( pattern = "yyyy-MM-dd HH:mm:ss",timezone="GMT+8")
private Date createdDate;
@JsonFormat( pattern = "yyyy-MM-dd HH:mm:ss")
private LocalDateTime createdTime;
【2】前臺傳String格式日期給後臺
如下所示，前臺傳參2020-08-30 11:11:11，後臺使用LocalDateTime 接收。
通常會報錯類似如下：
nested exception is org.springframework.core.convert.ConversionFailedException:
Failed to convert from type [java.lang.String] to type [java.time.LocalDateTime ]
很顯然是在參數綁定的時候沒有找到合適的轉換器把String轉換為對應的格式。
① 配置全局的日期轉換器localDateTimeConvert
@Bean
public Converter<String, LocalDateTime> localDateTimeConvert() {
return new Converter<String, LocalDateTime>() {
@Override
public LocalDateTime convert(String source) {
DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTime = null;
try {
//2020-01-01 00:00:00
switch (source.length()){
case 10:
logger.debug("傳過來的是日期格式：{}",source);
source=source+" 00:00:00";
break;
case 13:
logger.debug("傳過來的是日期 小時格式：{}",source);
source=source+":00:00";
break;
case 16:
logger.debug("傳過來的是日期 小時:分鐘格式：{}",source);
source=source+":00";
break;
}
dateTime = LocalDateTime.parse(source, df);
} catch (Exception e) {
logger.error(e.getMessage(),e);
}
return dateTime;
}
};
}
實現原理簡要描述
在進行參數綁定的時候，會使用WebDataBinder對象。而創建WebDataBinder對象時，會遍歷DefaultDataBinderFactory.initializer，使用其WebBindingInitializer initializer對WebDataBinder對象進行初始化。
初始化方法具體可見ConfigurableWebBindingInitializer.initBinder(WebDataBinder binder)，源碼如下：
public void initBinder(WebDataBinder binder) {
binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
if (this.directFieldAccess) {
binder.initDirectFieldAccess();
}
//設置messageCodesResolver
if (this.messageCodesResolver != null) {
binder.setMessageCodesResolver(this.messageCodesResolver);
}
//設置bindingErrorProcessor
if (this.bindingErrorProcessor != null) {
binder.setBindingErrorProcessor(this.bindingErrorProcessor);
}
//設置validator
if (this.validator != null && binder.getTarget() != null && this.validator.supports(binder.getTarget().getClass())) {
binder.setValidator(this.validator);
}
//設置conversionService
if (this.conversionService != null) {
binder.setConversionService(this.conversionService);
}
if (this.propertyEditorRegistrars != null) {
PropertyEditorRegistrar[] var2 = this.propertyEditorRegistrars;
int var3 = var2.length;
for(int var4 = 0; var4 < var3; ++var4) {
PropertyEditorRegistrar propertyEditorRegistrar = var2[var4];
propertyEditorRegistrar.registerCustomEditors(binder);
}
}
}
而conversionService中包含瞭許多的convert-類型格式化器。在WebDataBinder進行參數綁定的時候就會使用不同的格式化器即不同的convert進行參數類型轉換。
關於參數綁定的過程，有興趣的可以跟蹤DataBinder.doBind方法，在這個過程中會對前臺傳輸的值進行類型轉換為目標參數需要的類型。自定義的localDateTimeConvert也是在這裡被用到的。
如下所示前臺傳String格式給後臺參數endDate，參數類型為java.time.LocalDateTime。
找到我們自定義的converter
調用convert進行類型轉換：
可以看到轉換後的結果為：
② 配置日期格式化器
/**
* yyyy-MM-dd HH:mm:ss String-localDateTime
* @return
*/
@Bean
public Formatter<LocalDateTime> localDateTimeFormatter() {
return new Formatter<LocalDateTime>() {
@Override
public LocalDateTime parse(String text, Locale locale) throws ParseException {
return LocalDateTime.parse(text, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
}
@Override
public String print(LocalDateTime localDateTime, Locale locale) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
return formatter.format(localDateTime);
}
};
}
自定義的格式化器會在SpringBoot啟動時自動化配置過程中被加入，具體可以參考如下代碼。
WebMvcAutoConfiguration.mvcConversionService：
@Bean
@Override
public FormattingConversionService mvcConversionService() {
WebConversionService conversionService = new WebConversionService(this.mvcProperties.getDateFormat());
addFormatters(conversionService);
return conversionService;
}
【3】convert是什麼時候添加到ConversionService中的？
① SpringBoot啟動的時候運行run方法
其會走到SpringApplication.configureEnvironment方法處：
protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
if (this.addConversionService) {
//從這裡跟蹤
ConversionService conversionService = ApplicationConversionService.getSharedInstance();
environment.setConversionService((ConfigurableConversionService)conversionService);
}
this.configurePropertySources(environment, args);
this.configureProfiles(environment, args);
}
② 嘗試獲取ConversionService
ApplicationConversionService.getSharedInstance如下所示，這裡可以看到其使用瞭設計模式中的懶漢式之雙重校驗鎖來獲取單例。
public static ConversionService getSharedInstance() {
ApplicationConversionService sharedInstance = sharedInstance;
if (sharedInstance == null) {
Class var1 = ApplicationConversionService.class;
synchronized(ApplicationConversionService.class) {
sharedInstance = sharedInstance;
if (sharedInstance == null) {
sharedInstance = new ApplicationConversionService();
sharedInstance = sharedInstance;
}
}
}
return sharedInstance;
}
③ 獲取ApplicationConversionService
繼續對象創建過程會發現其走到瞭configure處：
public ApplicationConversionService(StringValueResolver embeddedValueResolver) {
if (embeddedValueResolver != null) {
this.setEmbeddedValueResolver(embeddedValueResolver);
}
//我們從這裡繼續跟進
configure(this);
}
這裡我們順帶看一下ApplicationConversionService的類繼承示意圖（其不隻是可以作為ConversionService還可以作為ConverterRegistry與FormatterRegistry）：
④ ApplicationConversionService.configure
創建ApplicationConversionService時會對其進行配置，這裡很重要。其會註入默認的Converter和Formatter：
public static void configure(FormatterRegistry registry) {
DefaultConversionService.addDefaultConverters(registry);
DefaultFormattingConversionService.addDefaultFormatters(registry);
addApplicationFormatters(registry);
addApplicationConverters(registry);
}
⑤ DefaultConversionService.addDefaultConverters
該方法執行完，會添加52個類型轉換器：
public static void addDefaultConverters(ConverterRegistry converterRegistry) {
addScalarConverters(converterRegistry);
addCollectionConverters(converterRegistry);
converterRegistry.addConverter(new ByteBufferConverter((ConversionService) converterRegistry));
converterRegistry.addConverter(new StringToTimeZoneConverter());
converterRegistry.addConverter(new ZoneIdToTimeZoneConverter());
converterRegistry.addConverter(new ZonedDateTimeToCalendarConverter());
converterRegistry.addConverter(new ObjectToObjectConverter());
converterRegistry.addConverter(new IdToEntityConverter((ConversionService) converterRegistry));
converterRegistry.addConverter(new FallbackObjectToStringConverter());
converterRegistry.addConverter(new ObjectToOptionalConverter((ConversionService) converterRegistry));
}
addScalarConverters(converterRegistry);如下所示：
private static void addScalarConverters(ConverterRegistry converterRegistry) {
converterRegistry.addConverterFactory(new NumberToNumberConverterFactory());
converterRegistry.addConverterFactory(new StringToNumberConverterFactory());
converterRegistry.addConverter(Number.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverter(new StringToCharacterConverter());
converterRegistry.addConverter(Character.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverter(new NumberToCharacterConverter());
converterRegistry.addConverterFactory(new CharacterToNumberFactory());
converterRegistry.addConverter(new StringToBooleanConverter());
converterRegistry.addConverter(Boolean.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverterFactory(new StringToEnumConverterFactory());
converterRegistry.addConverter(new EnumToStringConverter((ConversionService) converterRegistry));
converterRegistry.addConverterFactory(new IntegerToEnumConverterFactory());
converterRegistry.addConverter(new EnumToIntegerConverter((ConversionService) converterRegistry));
converterRegistry.addConverter(new StringToLocaleConverter());
converterRegistry.addConverter(Locale.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverter(new StringToCharsetConverter());
converterRegistry.addConverter(Charset.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverter(new StringToCurrencyConverter());
converterRegistry.addConverter(Currency.class, String.class, new ObjectToStringConverter());
converterRegistry.addConverter(new StringToPropertiesConverter());
converterRegistry.addConverter(new PropertiesToStringConverter());
converterRegistry.addConverter(new StringToUUIDConverter());
converterRegistry.addConverter(UUID.class, String.class, new ObjectToStringConverter());
}
這裡會添加23個類型轉換器：
添加集合處理的類型轉換器(這裡會添加17個類型轉換器)：
public static void addCollectionConverters(ConverterRegistry converterRegistry) {
ConversionService conversionService = (ConversionService) converterRegistry;
converterRegistry.addConverter(new ArrayToCollectionConverter(conversionService));
converterRegistry.addConverter(new CollectionToArrayConverter(conversionService));
converterRegistry.addConverter(new ArrayToArrayConverter(conversionService));
converterRegistry.addConverter(new CollectionToCollectionConverter(conversionService));
converterRegistry.addConverter(new MapToMapConverter(conversionService));
converterRegistry.addConverter(new ArrayToStringConverter(conversionService));
converterRegistry.addConverter(new StringToArrayConverter(conversionService));
converterRegistry.addConverter(new ArrayToObjectConverter(conversionService));
converterRegistry.addConverter(new ObjectToArrayConverter(conversionService));
converterRegistry.addConverter(new CollectionToStringConverter(conversionService));
converterRegistry.addConverter(new StringToCollectionConverter(conversionService));
converterRegistry.addConverter(new CollectionToObjectConverter(conversionService));
converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));
converterRegistry.addConverter(new StreamConverter(conversionService));
}
⑥ addDefaultFormatters添加格式化器
/**
* Add formatters appropriate for most environments: including number formatters,
* JSR-354 Money & Currency formatters, JSR-310 Date-Time and/or Joda-Time formatters,
* depending on the presence of the corresponding API on the classpath.
* @param formatterRegistry the service to register default formatters with
*/
public static void addDefaultFormatters(FormatterRegistry formatterRegistry) {
// Default handling of number values
formatterRegistry.addFormatterForFieldAnnotation(new NumberFormatAnnotationFormatterFactory());
// Default handling of monetary values
if (jsr354Present) {
formatterRegistry.addFormatter(new CurrencyUnitFormatter());
formatterRegistry.addFormatter(new MonetaryAmountFormatter());
formatterRegistry.addFormatterForFieldAnnotation(new Jsr354NumberFormatAnnotationFormatterFactory());
}
// Default handling of date-time values
// just handling JSR-310 specific date and time types
new DateTimeFormatterRegistrar().registerFormatters(formatterRegistry);
if (jodaTimePresent) {
// handles Joda-specific types as well as Date, Calendar, Long
new JodaTimeFormatterRegistrar().registerFormatters(formatterRegistry);
}
else {
// regular DateFormat-based Date, Calendar, Long converters
new DateFormatterRegistrar().registerFormatters(formatterRegistry);
}
}
DateTimeFormatterRegistrar.registerFormatters
@Override
public void registerFormatters(FormatterRegistry registry) {
DateTimeConverters.registerConverters(registry);
DateTimeFormatter df = getFormatter(Type.DATE);
DateTimeFormatter tf = getFormatter(Type.TIME);
DateTimeFormatter dtf = getFormatter(Type.DATE_TIME);
// Efficient ISO_LOCAL_* variants for printing since they are twice as fast...
registry.addFormatterForFieldType(LocalDate.class,
new TemporalAccessorPrinter(
df == DateTimeFormatter.ISO_DATE ? DateTimeFormatter.ISO_LOCAL_DATE : df),
new TemporalAccessorParser(LocalDate.class, df));
registry.addFormatterForFieldType(LocalTime.class,
new TemporalAccessorPrinter(
tf == DateTimeFormatter.ISO_TIME ? DateTimeFormatter.ISO_LOCAL_TIME : tf),
new TemporalAccessorParser(LocalTime.class, tf));
registry.addFormatterForFieldType(LocalDateTime.class,
new TemporalAccessorPrinter(
dtf == DateTimeFormatter.ISO_DATE_TIME ? DateTimeFormatter.ISO_LOCAL_DATE_TIME : dtf),
new TemporalAccessorParser(LocalDateTime.class, dtf));
registry.addFormatterForFieldType(ZonedDateTime.class,
new TemporalAccessorPrinter(dtf),
new TemporalAccessorParser(ZonedDateTime.class, dtf));
registry.addFormatterForFieldType(OffsetDateTime.class,
new TemporalAccessorPrinter(dtf),
new TemporalAccessorParser(OffsetDateTime.class, dtf));
registry.addFormatterForFieldType(OffsetTime.class,
new TemporalAccessorPrinter(tf),
new TemporalAccessorParser(OffsetTime.class, tf));
registry.addFormatterForFieldType(Instant.class, new InstantFormatter());
registry.addFormatterForFieldType(Period.class, new PeriodFormatter());
registry.addFormatterForFieldType(Duration.class, new DurationFormatter());
registry.addFormatterForFieldType(Year.class, new YearFormatter());
registry.addFormatterForFieldType(Month.class, new MonthFormatter());
registry.addFormatterForFieldType(YearMonth.class, new YearMonthFormatter());
registry.addFormatterForFieldType(MonthDay.class, new MonthDayFormatter());
registry.addFormatterForFieldAnnotation(new Jsr310DateTimeFormatAnnotationFormatterFactory());
}
DateTimeConverters.registerConverters
public static void registerConverters(ConverterRegistry registry) {
DateFormatterRegistrar.addDateConverters(registry);
registry.addConverter(new LocalDateTimeToLocalDateConverter());
registry.addConverter(new LocalDateTimeToLocalTimeConverter());
registry.addConverter(new ZonedDateTimeToLocalDateConverter());
registry.addConverter(new ZonedDateTimeToLocalTimeConverter());
registry.addConverter(new ZonedDateTimeToLocalDateTimeConverter());
registry.addConverter(new ZonedDateTimeToOffsetDateTimeConverter());
registry.addConverter(new ZonedDateTimeToInstantConverter());
registry.addConverter(new OffsetDateTimeToLocalDateConverter());
registry.addConverter(new OffsetDateTimeToLocalTimeConverter());
registry.addConverter(new OffsetDateTimeToLocalDateTimeConverter());
registry.addConverter(new OffsetDateTimeToZonedDateTimeConverter());
registry.addConverter(new OffsetDateTimeToInstantConverter());
registry.addConverter(new CalendarToZonedDateTimeConverter());
registry.addConverter(new CalendarToOffsetDateTimeConverter());
registry.addConverter(new CalendarToLocalDateConverter());
registry.addConverter(new CalendarToLocalTimeConverter());
registry.addConverter(new CalendarToLocalDateTimeConverter());
registry.addConverter(new CalendarToInstantConverter());
registry.addConverter(new LongToInstantConverter());
registry.addConverter(new InstantToLongConverter());
}
DateFormatterRegistrar.addDateConverters
public static void addDateConverters(ConverterRegistry converterRegistry) {
converterRegistry.addConverter(new DateToLongConverter());
converterRegistry.addConverter(new DateToCalendarConverter());
converterRegistry.addConverter(new CalendarToDateConverter());
converterRegistry.addConverter(new CalendarToLongConverter());
converterRegistry.addConverter(new LongToDateConverter());
converterRegistry.addConverter(new LongToCalendarConverter());
}
⑦ addApplicationFormatters(registry)
添加全局格式化器：
public static void addApplicationFormatters(FormatterRegistry registry) {
registry.addFormatter(new CharArrayFormatter());
registry.addFormatter(new InetAddressFormatter());
registry.addFormatter(new IsoOffsetFormatter());
}
⑧ addApplicationConverters(registry)
添加全局類型轉換器：
public static void addApplicationConverters(ConverterRegistry registry) {
addDelimitedStringConverters(registry);
registry.addConverter(new StringToDurationConverter());
registry.addConverter(new DurationToStringConverter());
registry.addConverter(new NumberToDurationConverter());
registry.addConverter(new DurationToNumberConverter());
registry.addConverter(new StringToDataSizeConverter());
registry.addConverter(new NumberToDataSizeConverter());
registry.addConverter(new StringToFileConverter());
registry.addConverterFactory(new LenientStringToEnumConverterFactory());
registry.addConverterFactory(new LenientBooleanToEnumConverterFactory());
}
public static void addDelimitedStringConverters(ConverterRegistry registry) {
ConversionService service = (ConversionService)registry;
registry.addConverter(new ArrayToDelimitedStringConverter(service));
registry.addConverter(new CollectionToDelimitedStringConverter(service));
registry.addConverter(new DelimitedStringToArrayConverter(service));
registry.addConverter(new DelimitedStringToCollectionConverter(service));
}
以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。
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