杰克逊定制日期序列化器

Question

我需要为类'日期序列化设置格式.我有杰克逊的版本,没有@JsonFormat.这就是为什么我写自定义类:

public class CDJsonDateSerializer extends JsonSerializer<Date>{

@Override
public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException {
    SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy");
    String dateString = dateFormat.format(date);
    jsonGenerator.writeString(dateString);
}

}

并用它:

@JsonSerialize(using = CDJsonDateSerializer.class)
private Date startDate;

但是,我有另一个具有不同日期格式的字段,我不想为序列化创建另一个类.我可以将所有需要的格式(如常量)添加到CDJsonDateSerializer类中,并使用注释设置所需的格式@JsonSerialize吗？像这样的东西:

@JsonSerialize(using = CDJsonDateSerializer.class, CDJsonDateSerializer.FIRST_FORMAT).

以下回答:

它经过一些修正后才有效.我改变了在createContextual方法中获取注释的方法:

@Override
public JsonSerializer createContextual(SerializationConfig serializationConfig, BeanProperty beanProperty) {
    return new CustomDateSerializer(beanProperty.getAnnotation(JsonDateFormat.class).value());
}

我已经将@JacksonAnnotation添加到我创建的新注释JsonDateFormat中:

@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonDateFormat {
   String value();
}

Answer 1

如果您不能使用Jackson 2中的@JsonFormat,我建议您引入自己的自定义注释,其中包含格式字段.然后,您的serailizer应实现ContextualSerializer接口以访问注释值.

以下是杰克逊1.9.X的一个例子:

public class JacksonDateFormat {
    @Retention(RetentionPolicy.RUNTIME)
    public static @interface MyJsonFormat {
        String value();
    }

    public static class Bean {
        @MyJsonFormat("dd.MM.yyyy") @JsonSerialize(using = MyDateSerializer.class)
        public final Date date1;

        @MyJsonFormat("yyyy-MM-dd") @JsonSerialize(using = MyDateSerializer.class)
        public final Date date2;

        public Bean(final Date date1, final Date date2) {
            this.date1 = date1;
            this.date2 = date2;
        }
    }

    public static class MyDateSerializer extends JsonSerializer<Date>
            implements ContextualSerializer {
        private final String format;

        private MyDateSerializer(final String format) {this.format = format;}

        public MyDateSerializer() {this.format = null;}

        @Override
        public void serialize(
                final Date value, final JsonGenerator jgen, final SerializerProvider provider)
                throws IOException {
            jgen.writeString(new SimpleDateFormat(format).format(value));
        }

        @Override
        public JsonSerializer createContextual(
                final SerializationConfig serializationConfig, final BeanProperty beanProperty)
                throws JsonMappingException {
            final AnnotatedElement annotated = beanProperty.getMember().getAnnotated();
            return new MyDateSerializer(annotated.getAnnotation(MyJsonFormat.class).value());
        }
    }

    public static void main(String[] args) throws IOException {
        final ObjectMapper mapper = new ObjectMapper();
        final Bean value = new Bean(new Date(), new Date());
        System.out.println(mapper
                        .writerWithDefaultPrettyPrinter()
                        .writeValueAsString(value));
    }
}

输出:

{
  "date1" : "02.12.2014",
  "date2" : "2014-12-02"
}

如果您有权访问,ObjectMapper则可以为所有Date类型注册自定义序列化程序,因此您需要更长时间才能添加@JsonSerialize注释.

这是一个例子:

final ObjectMapper mapper = new ObjectMapper();
final SimpleModule module = new SimpleModule("", Version.unknownVersion());
module.addSerializer(Date.class, new MyDateSerializer(null));
mapper.registerModule(module);