Double 需要 Jackson 序列化程序，并且需要在运行时指定精度 [英] Need Jackson serializer for Double and need to specify precision at runtime

问题描述

有很多关于为数字、货币等创建 Jackson 序列化程序的帖子.对于工程应用，通常需要根据单位或其他标准设置数字的精度.

There are many posts about creating Jackson serializers for numbers, currency, etc. For engineering applications, there is often a need to set the precision on numbers based on the units or other criteria.

例如，空间坐标可能被限制在小数点后 5 或 6 位，温度可能被限制在小数点后 2 位.具有太多数字或截断指数符号的默认序列化器行为不好.我需要的是这样的:

For example, spatial coordinates might be constrained to 5 or 6 digits after the decimal point, and temperature might be constrained to 2 digits after the decimal point. Default serializer behavior that has too many digits or truncated exponential notation is not good. What I need is something like:

@JsonSerialize(using=MyDoubleSerializer.class, precision=6) double myValue;

更好的是能够在运行时指定精度.我也在使用 MixIn.我可以为每个类编写一个序列化程序，但希望指定特定的值.

and better yet be able to specify the precision at run-time. I am also using a MixIn. I could write a serializer for each class but hoped to specify on specific values.

任何想法将不胜感激.

推荐答案

您可以使用 Jackson 的 ContextualSerializer 来实现所需的序列化，如下所示.

You may use Jackson's ContextualSerializer to achieve desired serialization as shown below.

首先，创建一个注解来捕获精度

Firstly, create an annotation to capture precision

@Target({ElementType.FIELD,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Precision {
    int precision();
}

接下来，为 Double 类型创建一个上下文序列化器，它在要序列化的字段上查找 Precision 注释，然后为指定的精度创建一个新的序列化器.>

Next, create a contextual serializer for Double type which looks for Precision annotation on the field to be serialized and then create a new serializer for the specified precision.

public class DoubleContextualSerializer extends JsonSerializer<Double> implements ContextualSerializer {

    private int precision = 0;

    public DoubleContextualSerializer (int precision) {
        this.precision = precision;
    }

    public DoubleContextualSerializer () {

    }

    @Override
    public void serialize(Double value, JsonGenerator gen, SerializerProvider serializers) throws IOException, JsonProcessingException {
        if (precision == 0) {
            gen.writeNumber(value.doubleValue());
        } else {
            BigDecimal bd = new BigDecimal(value);
            bd = bd.setScale(precision, RoundingMode.HALF_UP);
            gen.writeNumber(bd.doubleValue());
        }

    }
    @Override
    public JsonSerializer<?> createContextual(SerializerProvider prov, BeanProperty property) throws JsonMappingException {
        Precision precision = property.getAnnotation(Precision.class);
        if (precision != null) {
            return new DoubleContextualSerializer (precision.precision());
        }
        return this;
    }
}

最后，注释您的字段以使用自定义序列化程序并设置精度

Finally, annotate your field to use custom serializer and set precision

public class Bean{

   @JsonSerialize(using = DoubleContextualSerializer .class)
   @Precision(precision = 2)
   private double doubleNumber;

}

希望这有帮助！！

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