使用JAXB根据属性解析xml [英] Parse xml based on attributes using JAXB

问题描述

我正在使用JAXB解析一些xml.

I am using JAXB to parse some xml.

<countries>
    <Name language="en">Australia</Name>
    <Name language="se">Australien</Name>
</countries>

如果我在所在国家/地区使用

If I in my class Countries use

@XmlElement(name = "Name", required = true)
    protected List<Name> name;

一切正常. 但是我只想获取language ="en"

everything works. However I would like to only get the attribute where language="en"

所以我在我的国家/地区课程中有

So I in my Countries class have

protected String name

不是收藏集.

例如，是否可以通过一些注释来解决此问题?

Is there a good way to solve this with some annotation for example?

推荐答案

注意:我是 JAXB(JSR-222) 专家组

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group

以下是您处理此用例的两种方法.首先是更多代码，但是可以用任何JAXB实现来完成.第二个是更少的代码，但是需要您使用EclipseLink JAXB(MOXy).

Below are two ways you could handle this use case. The first is a little more code but could be done with any JAXB implementation. The second is less code, but requires you use EclipseLink JAXB (MOXy).

选项#1-任何JAXB(JSR-222)的实现

演示

Demo

您可以使用过滤的流读取器过滤掉不需要的元素，并使JAXB实现取消编组.

You could use a filtered stream reader to filter out the unwanted elements and have your JAXB implementation unmarshal that.

package forum11586106;

import javax.xml.bind.*;
import javax.xml.stream.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    private static final String LANGUAGE_CODE = "en";

    public static void main(String[] args) throws Exception {
        XMLInputFactory xif = XMLInputFactory.newFactory();
        XMLStreamReader xsr = xif.createXMLStreamReader(new StreamSource("src/forum11586106/input.xml"));
        xsr = xif.createFilteredReader(xsr, new StreamFilter() {

            private boolean isReading = true;

            @Override
            public boolean accept(XMLStreamReader reader) {
                if(reader.isStartElement() && "Name".equals(reader.getLocalName())) {
                    isReading = LANGUAGE_CODE.equals(reader.getAttributeValue("", "language"));
                    return isReading;
                } else if(reader.isEndElement() && !isReading) {
                    isReading = true;
                    return false;
                }

                return true;
            }});

        JAXBContext jc = JAXBContext.newInstance(Countries.class);
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Countries countries = (Countries) unmarshaller.unmarshal(xsr);

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

}

国家/地区

Countries

package forum11586106;

import javax.xml.bind.annotation.*;

@XmlRootElement
public class Countries {

    private String name;

    @XmlElement(name="Name")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

input.xml

input.xml

使用这种方法，输出中不包含language属性:

With this approach the language attribute is not included in the output:

<countries>
    <Name language="en">Australia</Name>
    <Name language="se">Australien</Name>
</countries>

输出

Output

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<countries>
    <Name>Australia</Name>
</countries>

---

选项#2-ECLIPSELINK JAXB(MOXy)

我们将利用MOXy的@XmlPath扩展名映射到具有值en的language属性的Name元素(请参阅

We will leverage MOXy's @XmlPath extension to map to the Name element that has a language attribute with value en (see http://blog.bdoughan.com/2011/03/map-to-element-based-on-attribute-value.html).

国家/地区

Countries

package forum11586106;

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

@XmlRootElement
public class Countries {

    private String name;

    @XmlPath("Name[@language='en']/text()")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

jaxb.properties

jaxb.properties

要将MOXy用作JAXB提供程序，您需要在与域模型相同的软件包中包含一个名为jaxb.properties的文件，并带有以下条目(请参阅:

To use MOXy as your JAXB provider you need to include a file called jaxb.properties in the same package as your domain model with the following entry (see: http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html).

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

演示

Demo

使用这种方法，元素过滤由@XmlPath映射处理，因此运行时部分变得更加简单.请注意如何仅使用标准的JAXB运行时API.

With this approach the element filtering is handled by the @XmlPath mapping, so the runtime portion becomes much simpler. Note how only the standard JAXB runtime APIs are used.

package forum11586106;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

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

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum11586106/input.xml");
        Countries countries = (Countries) unmarshaller.unmarshal(xml);

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

}

input.xml

input.xml

<countries>
    <Name language="en">Australia</Name>
    <Name language="se">Australien</Name>
</countries>

输出

Output

通过这种方法，language属性包含在输出中:

With this approach the language attribute is included in the output:

<?xml version="1.0" encoding="UTF-8"?>
<countries>
   <Name language="en">Australia</Name>
</countries>

这篇关于使用JAXB根据属性解析xml的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！