java JAXB XML 适配器通过注解工作，但不通过 setAdapter
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JAXB XML Adapters work via annotations but not via setAdapter
提问by I82Much
I understand all about how to use XMLAdaptersto 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).
我完全了解如何使用XMLAdapters来转换不可映射的类型，或者只是改变某些对象如何序列化/反序列化为 XML。如果我使用注释（包级别或其他级别），一切都会很好。问题是我试图更改我无法将源代码更改为的第三方对象的表示（即为了注入注释）。
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:
考虑到 Marshaller 对象具有手动添加适配器的方法，这应该不是问题。不幸的是，无论我做什么，我都无法以这种方式设置适配器以“启动”。例如，我有一个类表示 XYZ 空间（地心坐标）中的一个点。在我生成的 XML 中，我希望将其转换为纬度/经度/高度（大地坐标）。这是我的课程：
Geocentric
地心说
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;
}
}
Geodetic
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
地心到大地定位适配器
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 field
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();
}
}
}
Output:
输出：
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<objectWithLocation>
<location z="0.0" y="0.0" x="0.0"/>
</objectWithLocation>
By using an annotation (in my package-info.javafile):
通过使用注释（在我的package-info.java文件中）：
@javax.xml.bind.annotation.adapters.XmlJavaTypeAdapters
({
@javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter(value=GeocentricToGeodeticLocationAdapter.class,type=GeocentricCoordinate.class),
})
package package testJaxb;
I get the following (desired) xml
我得到以下（所需的）xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<objectWithLocation>
<location longitude="45.0" latitude="45.0" altitude="1000.0"/>
</objectWithLocation>
So my question is twofold.
所以我的问题是双重的。
- Why does the adapter work when annotated, but not when explicitly set via the
setAdaptermethod? - 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?
- 为什么适配器在注释时工作，但在通过
setAdapter方法显式设置时不起作用？ - 当我有无法注释的类以及无法修改其 package-info.java 以添加注释时，如何解决此问题？
回答by bdoughan
The setAdapter(XmlAdapter)on Marshalleris 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:
在setAdapter(XmlAdapter)对Marshaller使用在初始化XmlAdapter通过对已与注释的属性@XmlJavaTypeAdapter。下面的链接是我利用这种行为的答案：
If you want to map third party classes you could use EclipseLink JAXB (MOXy)'s XML mapping file (I'm the MOXy lead):
如果您想映射第三方类，您可以使用EclipseLink JAXB (MOXy)的 XML 映射文件（我是 MOXy 的负责人）：
回答by user1697575
You always have to annotate with @XmlJavaTypeAdapter(...).
你总是必须注释 @XmlJavaTypeAdapter(...).
marshaller.setAdapter(...)is means to assign a custom initialized instance of your type adapter in case you have non default constructor initialisation.
marshaller.setAdapter(...)是指分配类型适配器的自定义初始化实例，以防您有非默认构造函数初始化。
Otherwise, if you have only one default constructor for your adapter, then you don't need to explicitly call .setAdapter(...)method.
否则，如果您的适配器只有一个默认构造函数，则不需要显式调用.setAdapter(...)方法。
Here is a great answer with more detailed explanation: JAXB: Isn't it possible to use an XmlAdapter without @XmlJavaTypeAdapter?
这是一个带有更详细解释的很好的答案： JAXB：是否可以在没有 @XmlJavaTypeAdapter 的情况下使用 XmlAdapter？
JAXB Runtime can only accept Adapter with No-args constructor .. (Obviously JAXBContextdoes not know about application specific model)
JAXB 运行时只能接受带有无参数构造函数的适配器..（显然JAXBContext不知道应用程序特定模型）
So thankfully there is an option :D
谢天谢地，有一个选择：D
You can tell your unmarshaller to use given instance of UserAdapter rather than instating it by own its own.
您可以告诉您的解组器使用 UserAdapter 的给定实例，而不是自行安装它。
public class Test {
public static void main(String... args) {
JAXBContext context = JAXBContext.getInstance(Event.class);
Unmarshaller unmarshaller = context.createUnmarshaller();
UserContext userContext = null; // fetch it from some where
unmarshaller.setAdapter(UserAdapter.class, new UserAdapter(userContext));
Event event = (Event) unmarshaller.unmarshal(..);
}
}
setAdaptermethod is available on both Marshaller & Unmarshaller
setAdapter方法在 Marshaller 和 Unmarshaller 上都可用
Note:
setAdapter on marshaller / unmarshaller does not mean that you don't have to use @XmlJavaTypeAdapter.
注意： marshaller / unmarshaller 上的 setAdapter 并不意味着您不必使用@XmlJavaTypeAdapter.
