例外:“数据库行 [UnmarshalRecordImpl()] 中缺少类指示符字段."使用 EclipseLink JAXB (MOXy) 解组 XML 时

素材狗 2022-01-01 10:01:15 文章分类：Java问题点击数：1次

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Exception : quot;Missing class indicator field from database row [UnmarshalRecordImpl()].quot; when unmarshalling XML using EclipseLink JAXB (MOXy)(例外:“数据库行 [UnmarshalRecordImpl()] 中缺少类指示符字段.使用 EclipseLink JAXB (MOXy) 解组 XML 时)

本文介绍了例外:“数据库行 [UnmarshalRecordImpl()] 中缺少类指示符字段."使用 EclipseLink JAXB (MOXy) 解组 XML 时的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

是否可以通过 @XmlDescriminatorNode/@XmlDescrimintatorValue 注释解组下一个 XML，或任何解决方法:

Is it any way to unmarshalling with @XmlDescriminatorNode/@XmlDescrimintatorValue annotations next XML, or any workaround:

<assets>
    <asset type="full">
        <data_file role="source">
            <locale name="ru-RU"/>
        </data_file>
        <data_file role="extension">
            <locale name="ru-RU"/>
        </data_file>
        <data_file>
            <locale name="ru-RU"/>
        </data_file>
    </asset>
</assets>

我的映射类:

@XmlRootElement(name="data_file")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorNode("@role")
public abstract class BaseDataFile implements Serializable {

    @XmlPath("@role")
    @XmlAttribute(name = "role")
    private String role;

    public String getRole() {
        return role;
    }

    public void setRole(String role) {
        this.role = role;
    }
}

@XmlRootElement(name="data_file")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorValue("source")
public class SourceDataFile extends BaseDataFile {

}

@XmlRootElement(name="data_file")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorValue("source")
public class SourceDataFile extends BaseDataFile {

}

@XmlRootElement(name="data_file")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorValue("extension")
public class SourceDataFile extends BaseDataFile {

}

@XmlRootElement(name="asset")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorNode("@type")
public abstract class BaseAsset implements Serializable {

    @XmlPath("@type")
    @XmlAttribute(name = "type")
    private String type;

    @XmlPath("data_file")
    private List<BaseDataFile> dataFiles;

    public List<BaseDataFile> getDataFiles() {
        return dataFiles;
    }

    public void setDataFiles(List<BaseDataFile> dataFiles) {
        this.dataFiles = dataFiles;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }
}

如果 XML 包含如下元素，但没有 "type" 属性，则会发生错误:

The error occures if XML containes element as below, without "type" attribute:

<data_file>
  <locale name="ru-RU"/>
</data_file>

提前致谢

推荐答案

以下应该会有所帮助:

JAVA 模型

超类(BaseDataFile)

下面是您的 BaseDataFile 类的简化版本.由于您已将 XML 属性 role 映射为继承指示符，因此您无需将其也映射到对象模型中的属性.

Below is a simplified version of your BaseDataFile class. Since you have mapped the XML attribute role as the inheritance indicator you do not need to also map it to a property in your object model.

import java.io.Serializable;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorNode;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({SourceDataFile.class, ExtensionDataFile.class})
@XmlDiscriminatorNode("@role")
public abstract class BaseDataFile implements Serializable {

}

如果您真的想将 role XML 属性映射到对象模型中的属性，您应该使用 MOXy 的 @XmlReadOnly 属性来防止它被编组到 XML 文档(它已经写成继承指示符了).

If you really want to map the role XML attribute to a property in your object model you should use MOXy's @XmlReadOnly property to prevent it being marshalled to the XML document (it will already be wriiten as the inheritance indicator).

import java.io.Serializable;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorNode;
import org.eclipse.persistence.oxm.annotations.XmlReadOnly;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({SourceDataFile.class, ExtensionDataFile.class})
@XmlDiscriminatorNode("@role")
public abstract class BaseDataFile implements Serializable {

    @XmlAttribute
    @XmlReadOnly
    String role;

}

子类(SourceDataFile)

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

@XmlAccessorType(XmlAccessType.FIELD)
@XmlDiscriminatorValue("source")
public class SourceDataFile extends BaseDataFile {

}

<小时>

缺少继承指示符

基类不是抽象的

如果您的基类 (BaseDataFile) 不是抽象的，那么如果缺少继承指示符，则会创建一个基类的实例.

If your base class (BaseDataFile) had not been abstract then if the inheritance indicator was missing an instance of the base class would have been created.

基类是抽象的

由于您的基类是抽象的，MOXy 抱怨缺少继承指示符值:

Since your base class is abstract MOXy complained about the missing inheritance indicator value:

Exception in thread "main" Local Exception Stack: 
Exception [EclipseLink-44] (Eclipse Persistence Services - @VERSION@.@QUALIFIER@): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Missing class indicator field from database row [UnmarshalRecordImpl()].
Descriptor: XMLDescriptor(forum15597322.BaseDataFile --> [])
    at org.eclipse.persistence.exceptions.DescriptorException.missingClassIndicatorField(DescriptorException.java:957)
    at org.eclipse.persistence.internal.oxm.XMLRelationshipMappingNodeValue.processChild(XMLRelationshipMappingNodeValue.java:83)
    at org.eclipse.persistence.internal.oxm.XMLCompositeCollectionMappingNodeValue.startElement(XMLCompositeCollectionMappingNodeValue.java:184)
    at org.eclipse.persistence.internal.oxm.record.UnmarshalRecordImpl.startElement(UnmarshalRecordImpl.java:834)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:506)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:376)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2715)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:607)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:116)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:488)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:835)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:764)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:123)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1210)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:568)
    at org.eclipse.persistence.internal.oxm.record.XMLReader.parse(XMLReader.java:221)
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:895)
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:388)
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:366)
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:323)
    at org.eclipse.persistence.oxm.XMLUnmarshaller.unmarshal(XMLUnmarshaller.java:367)
    at org.eclipse.persistence.jaxb.JAXBUnmarshaller.unmarshal(JAXBUnmarshaller.java:123)
    at forum15597322.Demo.main(Demo.java:23)

<小时>

忽略错误

JAXB (JSR-222) 实现包括在编组/解组到 ValidationEventHandler 期间遇到的 MOXy 报告异常，当遇到缺少继承指示符值时，默认会出错.下面是设置自定义 ValidationEventHandler 的示例，该示例通过从 handleEvent 方法返回 true 来表示永不出错.

JAXB (JSR-222) implementations including MOXy report exceptions encountered during marshalling/unmarshaling to a ValidationEventHandler the default one will error out when a missing inheritance indicator value is encountered. Below is an example of setting a custom ValidationEventHandler that says never error out by returning true from the handleEvent method.

    Unmarshaller unmarshaller = jc.createUnmarshaller();
    unmarshaller.setEventHandler(new ValidationEventHandler() {
        @Override
        public boolean handleEvent(ValidationEvent event) {
            return true;
        }

    });

将这个答案放在一起时，我发现了以下 MOXy 错误，由于执行上述操作，该错误会将无效的文本值作为集合中的一个项目.该修复针对 EclipseLink 2.5.1.

While putting this answer together I found the following MOXy bug which as a result of doing the above will put an invalid text value as an item in the collection. The fix is targeted against EclipseLink 2.5.1.