使用MOXy读取XML时，如何将字段标记为必填/可选? [英] How do I mark fields as required/optional when reading XML with MOXy?

问题描述

具有这样的简单代码:

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
class A {
  @XmlPath("B/text()")
  private String b;

  @XmlPath("C/text()")
  private Integer c;
  ...
}

只要我在XML中具有apt值，它就可以正常工作.我想根据需要标记 c 字段，所以每次尝试读取未设置 c 或无效的文档时，MOXy都会抛出该异常.最简单的解决方案是什么?

It works absolutely fine as long as I have apt values in my XML. I'd like to mark the field c as required, so MOXy throw every time I try to read the document where c is either not set, or invalid. What's the easiest solution?

更新:

设置默认值也可以.

推荐答案

EclipseLink JAXB(MOXy)或任何JAXB实现都不会对丢失的节点执行设置操作，因此您可以执行以下操作:

EclipseLink JAXB (MOXy) or any JAXB implementation will not perform a set operation for missing nodes, so you could do the following:

选项1-默认字段值

import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
class A {
  @XmlPath("B/text()")
  private String b = "fieldDefault";

  @XmlPath("C/text()")
  private Integer c;
}

具有以下演示代码:

import java.io.StringReader;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;

public class Demo {

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

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        A a = (A) unmarshaller.unmarshal(new StringReader("<a/>"));

        System.out.println(a.getB());
        System.out.println(a.getC());
    }

}

将产生以下输出:

fieldDefault
null

选项#2-在 @XmlElement

Option #2 - Specify defaultValue on @XmlElement

您可以在 @XmlElement 批注上指定defaultValue，但这仅在解组空元素时才设置defaultValue.

You can specify a defaultValue on the @XmlElement annotation, but this will only set the defaultValue when an empty element is unmarshalled.

import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
class A {
  @XmlPath("B/text()")
  @XmlElement(defaultValue="annotationDefault")
  private String b;

  @XmlPath("C/text()")
  @XmlElement(defaultValue="annotationDefault")
  private Integer c;

}

带有以下演示代码:

import java.io.StringReader;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;

public class Demo {

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

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        A a = (A) unmarshaller.unmarshal(new StringReader("<a><B/></a>"));

        System.out.println(a.getB());
        System.out.println(a.getC());
    }

}

将产生以下输出:

annotationDefault
null

选项#3-在 Unmarshaller 上指定XML模式以强制进行验证

Option #3 - Specify an XML schema on the Unmarshaller to force validation

使用MOXy或任何JAXB实现，您可以在Unmarshaller上设置XML模式以验证输入:

Using MOXy or any JAXB implementation you can set an XML schema on the Unmarshaller to have the input validated:

• http://blog.bdoughan.com/2010/12/jaxb-and-marshalunmarshal-schema.html

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