java - Jaxb 编码预期为 xsi :nil ="true" in the element when the value is decimal which will be null,，但 xsi:nil ="true"未出现

Question

下面的代码生成下面给出的 xml，但没有 xsi:nil=true，为什么它没有生成该属性？

来自以下演示代码的 XML:

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <Market>
      <detail>
          <shipping available="false"/>
       </detail>
   </Market>

Jaxb 类用于从编码生成 xml 输出，我还添加了 @XmlElement(nillable = true) 注释。它没有在 xml 中输出 xsi:nil=true:

package com.jverstry.annotations.generics;

import java.math.BigDecimal;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
    "detail"
})
@XmlRootElement(name = "Market")
public class Market {

    @XmlElement(required = false)
    protected Detail detail;

    public Detail getDetail() {
        return detail;
    }

    public void setDetail(Detail detail) {
        this.detail = detail;
    }

    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = { "shipping"})
    public static class Detail {

        @XmlElementRef(name="shipping")
        protected JAXBElement<Shipping> shipping;

        public JAXBElement<Shipping> getShipping() {
            return shipping;
        }

        public void setShipping(JAXBElement<Shipping> value) {
            this.shipping = value;
        }


        @XmlAccessorType(XmlAccessType.FIELD)
        @XmlType(name = "", propOrder = { "value" })
        public static class Shipping {

            @XmlValue
            protected BigDecimal value;

            @XmlAttribute(name = "available")
            protected Boolean available;

            public BigDecimal getValue() {
                return value;
            }

            public void setValue(BigDecimal value) {
                this.value = value;
            }

            public Boolean getAvailable() {
                return available;
            }

            public void setAvailable(Boolean value) {
                this.available = value;
            }
        }
    }
}

ObjectFactory类:

package com.jverstry.annotations.generics;

import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.XmlElementDecl;
import javax.xml.bind.annotation.XmlRegistry;
import javax.xml.namespace.QName;

@XmlRegistry
public class ObjectFactory {

    @XmlElementDecl(name = "shipping")
    public JAXBElement<Market.Detail.Shipping> createShipping(Market.Detail.Shipping value) {
        return new JAXBElement<Market.Detail.Shipping>(new QName("shipping"), Market.Detail.Shipping.class, value);
    }
}

运行 jaxb 类来获取 xml:

package com.jverstry.annotations.generics;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Marshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Market.class,ObjectFactory.class);

        Market market = new Market();  
        Market.Detail md = new Market.Detail();

        Market.Detail.Shipping mds = new  Market.Detail.Shipping();
        mds.setAvailable(false);
        JAXBElement<Market.Detail.Shipping> shipping = new ObjectFactory().createShipping(mds);

        md.setShipping(shipping);
        market.setDetail(md);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(market, System.out);
    }
}

Answer 1

xsi:nil="true"的存在表示Market.Detail其 shipping 的对象属性是 null 。这里的情况并非如此 - 你有一个非空 Market.Detail.Shipping具有空值的对象。为了让xsi:nil与其他属性结合使用时，您必须声明 shipping属性(property)作为JAXBElement<Shipping>而不仅仅是Shipping :

    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = { "shipping"})
    public static class Detail
    {

        @XmlElement(nillable = true)
        protected JAXBElement<Market.Detail.Shipping> shipping;

        public JAXBElement<Market.Detail.Shipping> getShipping() {
            return shipping;
        }

        public void setShipping(JAXBElement<Market.Detail.Shipping> value) {
            this.shipping= value;
        }


        @XmlAccessorType(XmlAccessType.FIELD)
        @XmlType(name = "", propOrder = { "value" })
        public static class Shipping
        {
            // as before
        }
    }

现在<shipping available="false" xsi:nil="true"/>将由 JAXBElement 表示谁的isNil()返回true以及谁的getValue()是 Shipping 的非空实例谁的getAvailable()返回false .

<小时/>

根据您对问题的最新编辑 - 现在您拥有创建 JAXBElement<Shipping> 的基础架构实例你只需要设置 nil所需属性:

    Market.Detail.Shipping mds = new  Market.Detail.Shipping();
    mds.setAvailable(false);
    JAXBElement<Market.Detail.Shipping> shipping = new ObjectFactory().createShipping(mds);
    shipping.setNil(true); // mark the element as nil

    md.setShipping(shipping);