如何在JAXB封送期间添加XML处理指令

I would like to add a processing instruction whenever a collection/array property is serialized to get something like

我想在序列化时添加一个处理指令，以得到类似的结果。

<alice>
  <? array bob ?>
  <bob>edgar</bob>
  <bob>david</bob>
</alice>

Is this possible with JAXB? Or at least with some specific JAXB implementation?

JAXB能做到这一点吗?或者至少使用某些特定的JAXB实现?

1 个解决方案

#1

You could leverage an XMLStreamWriter and an XmlAdapter to do this:

您可以利用XMLStreamWriter和XmlAdapter来实现这一点:

BobAdapter

BobAdapter

Things to note about the XmlAdapter:

关于XmlAdapter需要注意的事项:

It's stateful and references an XMLStreamWriter. We will later leverage JAXB's ability to set a stateful XmlAdapter on a Marshaller.
它是有状态的，并引用XMLStreamWriter。稍后，我们将利用JAXB在编组器上设置有状态的XmlAdapter的能力。
It converts from a List<String> to a List<String>, we're just using an XmlAdapter here to get an event.
它从列表转换为列表，我们只是在这里使用XmlAdapter来获取事件。
The marshal method is where we call writeProcessingInstruction on the XMLStreamWriter:
marshal方法在XMLStreamWriter上调用writeprocessinginstructions:

package forum6931520;

import java.util.List;

import javax.xml.bind.annotation.adapters.XmlAdapter;
import javax.xml.stream.XMLStreamWriter;

public class BobAdapter extends XmlAdapter<List<String>, List<String>> {

    private boolean first = true;
    private XMLStreamWriter xmlStreamWriter;

    public BobAdapter() {
    }

    public BobAdapter(XMLStreamWriter xmlStreamWriter) {
        this();
        this.xmlStreamWriter = xmlStreamWriter;
    }

    @Override
    public List<String> marshal(List<String> stringList) throws Exception {
        if(first) {
            xmlStreamWriter.writeProcessingInstruction("array", "bob");
            first = false;
        }
        return stringList;
    }

    @Override
    public List<String> unmarshal(List<String> stringList) throws Exception {
        return stringList;
    }

}

Alice

爱丽丝

The @XmlJavaTypeAdapter annotation is used to link the XmlAdapter with the field/property:

@XmlJavaTypeAdapter注释用于将XmlAdapter与字段/属性联系起来:

package forum6931520;

import java.util.List;

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
public class Alice {

    private List<String> bob;

    @XmlJavaTypeAdapter(BobAdapter.class)
    public List<String> getBob() {
        return bob;
    }

    public void setBob(List<String> bob) {
        this.bob = bob;
    }

}

Demo

演示

package forum6931520;

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamWriter;

public class Demo {

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

        File xml = new File("src/forum6931520/input.xml");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Alice alice = (Alice) unmarshaller.unmarshal(xml);

        Marshaller marshaller = jc.createMarshaller();
        XMLOutputFactory xof = XMLOutputFactory.newFactory();
        XMLStreamWriter xmlStreamWriter = xof.createXMLStreamWriter(System.out);
        marshaller.setAdapter(new BobAdapter(xmlStreamWriter));
        marshaller.marshal(alice, xmlStreamWriter);
    }

}

input.xml

input.xml

<?xml version="1.0" encoding="UTF-8"?>
<alice>
  <?array bob?>
  <bob>edgar</bob>
  <bob>david</bob>
</alice>

Output

输出

<?xml version='1.0' encoding='UTF-8'?><alice><?array bob?><bob>edgar</bob><bob>david</bob></alice>

Note

请注意

This example needs to be run with EclipseLink JAXB (MOXy) as the JAXB RI will throw the following exception (I'm the MOXy lead):

这个示例需要使用EclipseLink JAXB (MOXy)运行，因为JAXB RI将抛出以下异常(我是MOXy的引子):

Exception in thread "main" com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
java.util.List is an interface, and JAXB can't handle interfaces.
    this problem is related to the following location:
        at java.util.List
        at public java.util.List forum6931520.Alice.getBob()
        at forum6931520.Alice
java.util.List does not have a no-arg default constructor.
    this problem is related to the following location:
        at java.util.List
        at public java.util.List forum6931520.Alice.getBob()
        at forum6931520.Alice

For More Information

的更多信息

http://blog.bdoughan.com/2010/07/xmladapter-jaxbs-secret-weapon.html
http://blog.bdoughan.com/2010/07/xmladapter-jaxbs-secret-weapon.html
http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html
http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html

UPDATE

更新

I have entered an enhancement request (https://bugs.eclipse.org/354286) to add native support for processing instructions. This would eventually allow you to specify the following on your property:

我输入了一个增强请求(https://bugs.eclipse.org/354286)来为处理指令添加本地支持。这将最终允许您在您的财产上指定以下内容:

@XmlProcessingInstruction(target="array", value="bob")
public List<String> getBob() {
    return bob;
}

#1