如何告诉 JAXB 忽略来自父类的属性

Question

我在使用 JAXB 时面临以下问题： 看起来 JAXB 正在分析从最深的子类到父类的属性，并且子属性具有优先级。我想以某种方式改变这种行为。特别是：

子类：

package test.sub;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlTransient;


@XmlAccessorType(XmlAccessType.NONE)
public class BasicDocument {

    private String comment;

    public String getComment() {
        return comment;
    }

    public void setComment(String cost) {
        this.comment = cost;
    }
}

父类：

package test;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;

import test.sub.BasicDocument;

@XmlRootElement(name="Description", namespace="http://www.w3.org/1999/02/22-rdf-syntax-ns#")
@XmlAccessorType(XmlAccessType.PROPERTY)
class Document extends BasicDocument {

    private String identifier;

    @XmlElement(name = "identifier", namespace = "http://purl.org/dc/terms/")
    public String getIdentifier() {
        return identifier;
    }

    public void setIdentifier(String identifier) {
        this.identifier = identifier;
    }

    @Override
    @XmlElement(name = "abstract", namespace = "http://purl.org/dc/terms/")
    public String getComment() {
        return super.getComment();
    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
    }
}

编组工作正常：

Document document = new Document();

document.setIdentifier("12A");
document.setComment("special");

StringWriter w = new StringWriter();

jaxbContext.createMarshaller().marshal(document, new StreamResult(w));

System.out.println(w);

输出：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:Description xmlns:ns2="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://purl.org/dc/terms/">
    <abstract>special</abstract>
    <identifier>12A</identifier>
</ns2:Description>

但是编组忽略了子 BasicDocument 类中的属性（t.xml 正是上面的 XML）：

JAXBContext jaxbContext = JAXBContext.newInstance(Document.class);

Document document = (Document) jaxbContext.createUnmarshaller().unmarshal(Document.class.getResourceAsStream("t.xml"));

System.out.println("out: " + document);

输出：

out: Document[identifier=12A,comment=<null>]

预期：

out: Document[identifier=12A,comment=special]

基本上@XmlAccessorType(XmlAccessType.NONE) 上的BasicDocument（见Ignore a parent class when Serializing to XML）没有效果。还像这样在包test.sub（参见@XmlTransient on third-party or external super class）中创建package-info.java：

@XmlAccessorType(XmlAccessType.NONE)
package test.sub;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;

没有效果。只有@XmlTransient public class BasicDocument 有效。理想情况下，我不想在孩子上添加任何注释，并且只能通过package-info.java 控制此行为。我该怎么做？

在 JDK 1.6.0_27 上测试，另外在类路径中使用 JAXB 2.2.4-1 运行时。

是功能还是错误？

Answer 1

您只需将setComment 方法添加到Document 类。没有它，即使该方法存在于父类中，它也会被视为只写属性。

public void setComment(String comment) {
    super.setComment(comment);
}

Document的完整源代码

package test;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;

import test.sub.BasicDocument;

@XmlRootElement(name="Description", namespace="http://www.w3.org/1999/02/22-rdf-syntax-ns#")
@XmlAccessorType(XmlAccessType.PROPERTY)
class Document extends BasicDocument {

    private String identifier;

    @XmlElement(name = "identifier", namespace = "http://purl.org/dc/terms/")
    public String getIdentifier() {
        return identifier;
    }

    public void setIdentifier(String identifier) {
        this.identifier = identifier;
    }

    @Override
    @XmlElement(name = "abstract", namespace = "http://purl.org/dc/terms/")
    public String getComment() {
        return super.getComment();
    }

    public void setComment(String comment) {
        super.setComment(comment);
    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
    }

}