如何设置JAXB的浮点格式(使用Eclipse Moxy的json) [英] How to set floating point format for JAXB (json using eclipse moxy)

问题描述

我有一个简单的pojo课:

I have a simple pojo class:

@XmlRootElement
public static class MyClass {
  private double f; //[0-1]

  @XmlAttribute
  //@XmlJavaTypeAdapter(FixedFloatingPointXmlAdapter.class) <-- has issues
  public double getF() {
    return f;
  }
}

字段f保持[0,1]范围内的值，有时可能很小.我想避免看到像1.234E-7(科学记法)之类的东西，而是想设置用于打印字段f的格式.

field f holds values in the range [0,1], which can sometimes be small. I'd like to avoid seeing things like 1.234E-7 (scientific notation) and would like to set the format used to print field f.

我看过其他建议使用XmlAdapter的答案，例如:

I've seen other answers that suggest using an XmlAdapter for this, like so:

public class FixedFloatingPointXmlAdapter extends XmlAdapter<String, Double> {
  private static final DecimalFormat FORMAT = new DecimalFormat("0.00000000");

  @Override
  public Double unmarshal(String v) throws Exception {
    return v == null ? null : Double.parseDouble(v);
  }

  @Override
  public String marshal(Double v) throws Exception {
    return v == null ? null : FORMAT.format(v);
  }
}

但是问题是该值将以json STRING 的形式打印出来(因此，"0.25000000" 而不是 0.25000000 )-因为XmlAdapter返回一个字符串(不是因为FORMAT放置了引号.它没有)

but the problem with this is that the value would be printed out as a json STRING (so "0.25000000" instead of 0.25000000) - because the XmlAdapter returns a String (not because FORMAT places quotes. it doesnt)

是否有任何JAXB/moxy注释可以使我控制格式而无需将字段转换为json字符串?

is there any JAXB/moxy annotation that would allow me to control the formatting without turning the field into a json string?

推荐答案

此解决方案正在使用 EclipseLink MOXy 的"nofollow noreferrer>转换注释.

This solution is using transformation annotations of EclipseLink MOXy.

import org.eclipse.persistence.oxm.annotations.XmlTransformation;
import org.eclipse.persistence.oxm.annotations.XmlWriteTransformer;

@XmlRootElement
public static class MyClass {
  @XmlAttribute
  @XmlReadTransformer(transformerClass=FixedFloatingTransformer.class)
  @XmlWriteTransformer(xmlPath="@f", transformerClass=FixedFloatingTransformer.class)
  private double f; //[0-1]

  public double getF() {
    return f;
  }
}

这是 transformerClass 的实现.

import java.text.DecimalFormat;

import org.eclipse.persistence.mappings.foundation.AbstractTransformationMapping;
import org.eclipse.persistence.mappings.transformers.AttributeTransformer;
import org.eclipse.persistence.mappings.transformers.FieldTransformer;
import org.eclipse.persistence.sessions.Record;
import org.eclipse.persistence.sessions.Session;

public class FixedFloatingTransformer implements FieldTransformer, AttributeTransformer { 
  private AbstractTransformationMapping mapping;
  private static DecimalFormat FORMAT = new DecimalFormat("0.00000000");

  public Object buildAttributeValue(Record r, Object obj, Session arg2) {
    return r.get(mapping.getFields().get(0));
  }

  public Object buildFieldValue(Object instance, String xpath, Session session) {
    Object o2 = mapping.getAttributeValueFromObject(instance);
    if (o2 instanceof Number) {
      return ((DecimalFormat)FORMAT.clone()).format((Number)o2);
    }
    return null;
  }

  public void initialize(AbstractTransformationMapping mapping) {
    this.mapping = mapping;
  }
}

2016年12月13日更新

moxy 将对象解组为JSON字符串时，将引用 @XmlSchemaType .如果 name 是 boolean 或 number type ，则 moxy 将输出不带引号char的值字符串.

Update in 2016/12/13

The @XmlSchemaType are referenced when moxy unmarshal the object to JSON string. If the name is boolean or number type, moxy will outputed the value string without quoted char.

示例1:您必须将格式值设置为 f .

public static class MyClass {
  private String f;

  @XmlAttribute
  @XmlSchemaType(name="double")
  public String getF() {
    return f;
  }
}

示例2:添加额外的吸气剂以返回格式化的值.

Sample 2 : Add extra getter to return formatted value.

public static class MyClass {
  private double f;

  @XmlTransient //preventing the mapping
  public double getF() {
    return f;
  }

  @XmlAttribute(name="f")
  @XmlSchemaType(name="double")
  public String getFAsString() {
    return new DecimalFormat("0.00000000").format(f);
  }
}

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