杰克逊定制日期序列化器 [英] Jackson custom date serializer

问题描述

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：

I need to set format for class' date serialization. I have the version of Jackson, which doesn't have @JsonFormat. That's Why I wrote custom class:

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);
}

}

并使用它：

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

但是，我有另外一个具有不同日期格式的字段，我不想创建另一个类用于序列化。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 @JsonSerialize 设置所需的格式吗？
这样的事情：

But, I have another fields which have different date's formats and I don't want to create another classes for serialization. Can I add all needed formats like constants to CDJsonDateSerializer class and set needed format with annotation @JsonSerialize ? Something like this:

@JsonSerialize（使用= CDJsonDateSerializer.class，CDJsonDateSerializer.FIRST_FORMAT）。

以后的回答：

经过一些修正后，它可以运作。我已经改变了在 createContextual 方法中获取注释的方式：

It works after some corrections. I've changed the way of getting annotation in createContextual method:

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

我已将 @JacksonAnnotation 添加到我的创建了新的注释JsonDateFormat：

And I've added @JacksonAnnotation to my created new annotation JsonDateFormat:

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

推荐答案

如果你不能使用 @JsonFormat ，我建议你介绍一下你自己的自定义注释，它将包含格式字段。然后你的选择器应该实现 ContextualSerializer 界面来访问注释值。

If you cannot use @JsonFormat from Jackson 2, I'd recommend you to introduce your own custom annotation which will contain the format field. Your serailizer should then implement the ContextualSerializer interface to get access to the annotation value.

以下是杰克逊的一个例子1.9.X：

Here is an example for Jackson 1.9.X:

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"
}

如果你有权访问 ObjectMapper 你可以为所有 Date 类型注册自定义序列化程序，因此您需要更长时间来放置 @JsonSerialize 注释。

If you have access to the ObjectMapper you can register your custom serializer for all the Date types, so you want longer need to put @JsonSerialize annotation.

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);

这篇关于杰克逊定制日期序列化器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！