注释向元素添加属性 [英] annotating the addition of an attribute to an element

问题描述

本着这种精神，我正在升级目前具有XML表示形式的Java对象:

I'm upgrading a Java object that currently has XML representation in this spirit:

<myObjects>
    <myObject uid="42" type="someEnum">
        <name>Waldo</name>
        <description>yada yada</description>
        <myElement>some_string</myElement>
        ...
    </myObject>
    ...
</myObjects>

myElement 是可选的-在Java中可以为null，在XML中可以省略.
如果 myElement 具有实际值，我将添加与仅相关的字段 (并且为了与以前的XML兼容，它本身是可选的)

myElement is optional - it can be null in Java / omitted in XML.
I'm adding a field that is only relevant if myElement has an actual value (and to keep compatibility with previous XML, it's optional in itself)

我正试图避免这种情况:

I'm trying to avoid this:

    <myElement>some_string</myElement>
    <myAttr>foo</myAttr>

并且喜欢这样的东西:

    <myElement myAttr="foo">some_string</myElement>

但是现在如何敲打我的头两天要如何注释它.

but banging my head for 2 days now on how to annotate it.

• 我考虑过用 XmlTransient 进行标记，然后让 XmlAnyElement 进行编组时捕获它-但是在将对象从Java编组到Java时，这似乎会引起问题. XML.
• 我尝试为该元素创建一个 XmlAdapter -但是unmarshal方法仅获取内部内容("some_string"). 我是否缺少这种技术?
• 有没有办法将元素作为字符串(< myElement myAttr = \" foo \> some_string</myElement>")获得，我将处理是我自己吗?
• 您是否建议其他方法?

• I thought of marking it with XmlTransient and let an XmlAnyElement catch it instead while unmarshalling - but it seems this will cause a problem when marshalling the object back from Java to XML.
• I tried creating an XmlAdapter for the element - but the unmarshal method gets only the inner content ("some_string"). Am I missing something with this technique?
• Is there a way to just get the element as a string ("<myElement myAttr=\"foo\">some_string</myElement>") and I will process it myself?
• Do you recommend any other approach?

推荐答案

您可以使用 EclipseLink JAXB (MOXy) @XmlPath扩展即可轻松实现:

You can use the EclipseLink JAXB (MOXy) @XmlPath extension to easily accomplish this:

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

import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class MyObject {

    @XmlAttribute
    private int uid;

    @XmlAttribute
    private String type;

    private String name;

    private String description;

    private String myElement;

    @XmlPath("myElement/@myAttr")
    private String myAttr;

}

此类将与以下XML交互:

This class will interact with the following XML:

<myObject uid="42" type="someEnum">
    <name>Waldo</name>
    <description>yada yada</description>
    <myElement myAttr="foo">some_string</myElement>
</myObject>

使用以下演示代码:

import java.io.File;

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

public class Demo {

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

        File file = new File("input.xml");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        MyObject myObject = (MyObject) unmarshaller.unmarshal(file);

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

}

要将MOXy指定为JAXB实现，您需要在与模型类相同的包中包含一个名为jaxb.properties的文件，并带有以下条目:

To specify MOXy as your JAXB implementation you need to include a file called jaxb.properties in the same package as your model classes with the following entry:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

有关基于MOXy的XPath映射的更多信息，请参见:

For more information on MOXy's XPath based mapping see:

• http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html
• http://bdoughan.blogspot.com/2010/07/xpath-based-mapping.html

• http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html
• http://bdoughan.blogspot.com/2010/07/xpath-based-mapping.html

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