JAXB XML Adapters通过注释工作，但不通过setAdapter工作 [英] JAXB XML Adapters work via annotations but not via setAdapter

问题描述

我完全了解如何使用 XMLAdapters 到转换不可映射的类型，或者只是改变某些对象被序列化/反序列化为XML的方式。如果我使用注释（包级别或其他），一切都很好。问题是我试图改变第三方对象的表示，我无法将源代码更改为（即为了注入注释）。

I understand all about how to use XMLAdapters to convert unmappable types, or just to change how certain objects are serialized/deserialized to XML. Everything works great if I use annotations (either package level or otherwise). The problem is that I am attempting to change the representations of third party objects which I cannot change the source code to (i.e. in order to inject annotations).

那应该是'这是一个问题，考虑到Marshaller对象有一个方法手动添加适配器。不幸的是，无论我做什么，我都无法通过这种方式设置适配器来启动。例如，我有一个表示XYZ空间中的点的类（地心坐标）。在我生成的XML中，我希望将其转换为lat / long / altitude（大地坐标）。以下是我的课程：

That shouldn't be a problem, considering that the Marshaller object has a method for manually adding adapters. Unfortunately, no matter what I do, I can't get the adapters set in this way to "kick in". For instance, I have a class representing a point in XYZ space (geocentric coordinates). In the XML I produce, I want this to be converted into lat/long/altitude (geodetic coordinates). Here are my classes:

Geocentric

package testJaxb;

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

@XmlRootElement
public class GeocentricCoordinate {
    // Units are in meters; see http://en.wikipedia.org/wiki/Geocentric_coordinates
    private double x;
    private double y;
    private double z;

    @XmlAttribute
    public double getX() {
        return x;
    }
    public void setX(double x) {
        this.x = x;
    }
    @XmlAttribute
    public double getY() {
        return y;
    }
    public void setY(double y) {
        this.y = y;
    }
    @XmlAttribute
    public double getZ() {
        return z;
    }
    public void setZ(double z) {
        this.z = z;
    }
}

大地测量

package testJaxb;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;
/**
 * @see http://en.wikipedia.org/wiki/Geodetic_system
 */
@XmlRootElement
public class GeodeticCoordinate {

    private double latitude;
    private double longitude;
    // Meters
    private double altitude;

    public GeodeticCoordinate() {
        this(0,0,0);
    }

    public GeodeticCoordinate(double latitude, double longitude, double altitude) {
        super();
        this.latitude = latitude;
        this.longitude = longitude;
        this.altitude = altitude;
    }

    @XmlAttribute
    public double getLatitude() {
        return latitude;
    }
    public void setLatitude(double latitude) {
        this.latitude = latitude;
    }

    @XmlAttribute
    public double getLongitude() {
        return longitude;
    }

    public void setLongitude(double longitude) {
        this.longitude = longitude;
    }

    @XmlAttribute
    public double getAltitude() {
        return altitude;
    }
    public void setAltitude(double altitude) {
        this.altitude = altitude;
    }



}

GeocentricToGeodeticLocationAdapter

package testJaxb;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.adapters.XmlAdapter;


/**
 * One of our systems uses xyz coordinates to represent locations. Consumers of our XML would much
 * prefer lat/lon/altitude.  This handles converting between xyz and lat lon alt.  
 * 
 * @author ndunn
 *
 */
public class GeocentricToGeodeticLocationAdapter extends XmlAdapter<GeodeticCoordinate,GeocentricCoordinate> {

    @Override
    public GeodeticCoordinate marshal(GeocentricCoordinate arg0) throws Exception {
        // TODO: do a real coordinate transformation
        GeodeticCoordinate coordinate = new GeodeticCoordinate();
        coordinate.setLatitude(45);
        coordinate.setLongitude(45);
        coordinate.setAltitude(1000);
        return coordinate;
    }

    @Override
    public GeocentricCoordinate unmarshal(GeodeticCoordinate arg0) throws Exception {
        // TODO do a real coordinate transformation
        GeocentricCoordinate gcc = new GeocentricCoordinate();
        gcc.setX(100);
        gcc.setY(200);
        gcc.setZ(300);
        return gcc;
    }
}

ObjectWithLocation字段

package testJaxb; 
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class ObjectWithLocation {

    private GeocentricCoordinate location = new GeocentricCoordinate();

    public GeocentricCoordinate getLocation() {
        return location;
    }

    public void setLocation(GeocentricCoordinate location) {
        this.location = location;
    }


    public static void main(String[] args) {

        ObjectWithLocation object = new ObjectWithLocation();

        try {
            JAXBContext context = JAXBContext.newInstance(ObjectWithLocation.class, GeodeticCoordinate.class, GeocentricCoordinate.class);
            Marshaller marshaller = context.createMarshaller();

            marshaller.setAdapter(new GeocentricToGeodeticLocationAdapter());
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

            marshaller.marshal(object, System.out);

        }
        catch (JAXBException jaxb) {
            jaxb.printStackTrace();
        }
    }
}

输出：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<objectWithLocation>
    <location z="0.0" y="0.0" x="0.0"/>
</objectWithLocation>

使用注释（在我的 package-info.java file）：

By using an annotation (in my package-info.java file):

@javax.xml.bind.annotation.adapters.XmlJavaTypeAdapters
({
@javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter(value=GeocentricToGeodeticLocationAdapter.class,type=GeocentricCoordinate.class),
})

package package testJaxb;

我得到以下（所需）xml

I get the following (desired) xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<objectWithLocation>
    <location longitude="45.0" latitude="45.0" altitude="1000.0"/>
</objectWithLocation>

所以我的问题是双重的。

So my question is twofold.

1. 为什么适配器在注释时有效，但是在通过 setAdapter 方法显式设置时却没有？


2. 如何当我有一些我无法注释的类和我的package-info.java我无法修改以添加注释时，我能解决这个问题吗？

1. Why does the adapter work when annotated, but not when explicitly set via the setAdapter method?
2. How do I work around this problem when I have classes that I cannot annotate and whose package-info.java I cannot modify in order to add the annotations?

推荐答案

Marshaller 上的 setAdapter（XmlAdapter）用于传入已初始化的XmlAdapter，以获取已使用 @XmlJavaTypeAdapter 注释的属性。以下链接是我利用此行为的答案：

The setAdapter(XmlAdapter) on Marshaller is used to pass in an initialized XmlAdapter for a property that is already annotated with @XmlJavaTypeAdapter. The link below is to an answer where I leverage this behaviour:

• 使用JAXB交叉引用两个XML文件中的XmlID

• Using JAXB to cross reference XmlIDs from two XML files

如果你想映射第三方类，可以使用 EclipseLink JAXB（MOXy）的XML映射文件（我是MOXy主管）：

If you want to map third party classes you could use EclipseLink JAXB (MOXy)'s XML mapping file (I'm the MOXy lead):

• http://bdoughan.blogspot.com/2010/12/extending- jaxb-represent-annotations.html

• http://bdoughan.blogspot.com/2010/12/extending-jaxb-representing-annotations.html

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