Spring中字段格式化的使用详解

自定义注解解析器。

public class StringToDateFormatter implements AnnotationFormatterFactory {
  @Override
  public Set> getFieldTypes() {
    return new HashSet>(Arrays.asList(Date.class));
  }
  @Override
  public Printer getPrinter(DateFormatter annotation, Class fieldType) {
    return getFormatter(annotation, fieldType);
  }
  @Override
  public Parser getParser(DateFormatter annotation, Class fieldType) {
    return getFormatter(annotation, fieldType);
  }
  private StringFormatter getFormatter(DateFormatter annotation, Class fieldType) {
    String pattern = annotation.value();
    return new StringFormatter(pattern);
  }
  class StringFormatter implements Formatter {
    private String pattern;
    public StringFormatter(String pattern) {
      this.pattern = pattern;
    }
    @Override
    public String print(Date date, Locale locale) {
      return DateTimeFormatter.ofPattern(pattern, locale).format(date.toInstant());
    }
    @Override
    public Date parse(String text, Locale locale) throws ParseException {
      DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern, locale);
      return Date.from(LocalDate.parse(text, formatter).atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());
    }
  }
}

注册及使用：

public class Main {
  @DateFormatter("yyyy年MM月dd日")
  private Date date;
  public static void main(String[] args) throws Exception {
    FormattingConversionService fcs = new FormattingConversionService();
    fcs.addFormatterForFieldAnnotation(new StringToDateFormatter());
    Main main = new Main();
    Field field = main.getClass().getDeclaredField("date");
    TypeDescriptor targetType = new TypeDescriptor(field);
    Object result = fcs.convert("2022年01月21日", targetType);
    System.out.println(result);
    field.setAccessible(true);
    field.set(main, result);
    System.out.println(main.date);
  }
}

3、FormatterRegistry

FormatterRegistry是用于注册格式化程序和转换器的SPI。FormattingConversionService是FormatterRegistry的一个实现，适用于大多数环境。可以通过编程或声明的方式将该变体配置为Spring bean，例如使用FormattingConversionServiceFactoryBean。因为这个实现还实现了ConversionService，所以您可以直接配置它，以便与Spring的DataBinder和Spring表达式语言(SpEL)一起使用。

public interface FormatterRegistry extends ConverterRegistry {
  void addPrinter(Printer printer);
  void addParser(Parser parser);
  void addFormatter(Formatter formatter);
  void addFormatterForFieldType(Class fieldType, Formatter formatter);
  void addFormatterForFieldType(Class fieldType, Printer printer, Parser parser);
  void addFormatterForFieldAnnotation(AnnotationFormatterFactory annotationFormatterFactory);
}

4、SpringMVC中配置类型转换

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
  @Override
  public void addFormatters(FormatterRegistry registry) {
    // ...
  }
}

SpringBoot中有如下的默认类型转换器。

public class WebMvcAutoConfiguration {
  public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
    @Bean
    @Override
    public FormattingConversionService mvcConversionService() {
      Format format = this.mvcProperties.getFormat();
      WebConversionService conversionService = new WebConversionService(new DateTimeFormatters().dateFormat(format.getDate()).timeFormat(format.getTime()).dateTimeFormat(format.getDateTime()));
      addFormatters(conversionService);
      return conversionService;
    }    
  }
}