问题描述
是否可以使用 JAXB 根据 xml 的属性将 xml 解组为特定的 Java 类?
Is it possible to use JAXB to unmarshall xml to a specific Java class based on an attribute of the xml?
<shapes>
<shape type="square" points="4" square-specific-attribute="foo" />
<shape type="triangle" points="3" triangle-specific-attribute="bar" />
</shapes>
我想要一个包含三角形和正方形的 Shape 对象列表，每个对象都有自己的特定于形状的属性.IE:
I would like to have a List of Shape objects containing a triangle and a square, each with their own shape-specific attribute. IE:
abstract class Shape {
int points;
//...etc
}
class Square extends Shape {
String square-specific-attribute;
//...etc
}
class Triangle extends Shape {
String triangle-specific-attribute;
//...etc
}
我目前只是将所有属性放在一个大的Shape"类中，但并不理想.
I'm currently just putting all attributes in one big "Shape" class and it's less than ideal.
如果形状被正确命名为 xml 元素，我可以让它工作，但不幸的是我无法控制我正在检索的 xml.
I could get this to work if the shapes were properly named xml elements, but unfortunately I don't have control of the xml I'm retrieving.
谢谢！
推荐答案
JAXB 是一个规范，具体的实现会提供扩展点来做这样的事情.如果您使用 EclipseLink JAXB (MOXy)，您可以按如下方式修改 Shape 类:
JAXB is a spec, specific implementations will provide extension points to do things such as this. If you are using EclipseLink JAXB (MOXy) you could modify the Shape class as follows:
import javax.xml.bind.annotation.XmlAttribute;
import org.eclipse.persistence.oxm.annotations.XmlCustomizer;
@XmlCustomizer(ShapeCustomizer.class)
public abstract class Shape {
int points;
@XmlAttribute
public int getPoints() {
return points;
}
public void setPoints(int points) {
this.points = points;
}
}
然后使用 MOXy @XMLCustomizer，您可以访问 InheritancePolicy 并将类指示符字段从@xsi:type"更改为type":
Then using the MOXy @XMLCustomizer you could access the InheritancePolicy and change the class indicator field from "@xsi:type" to just "type":
import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
public class ShapeCustomizer implements DescriptorCustomizer {
@Override
public void customize(ClassDescriptor descriptor) throws Exception {
descriptor.getInheritancePolicy().setClassIndicatorFieldName("@type");
}
}
您需要确保在模型类(Shape、Square 等)中有一个 jaxb.properties 文件，并使用以下条目指定 EclipseLink MOXy JAXB 实现:
You will need to ensure that you have a jaxb.properties file in with you model classes (Shape, Square, etc) with the following entry specifying the EclipseLink MOXy JAXB implementation:
javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
以下是其余的模型类:
形状
import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class Shapes {
private List<Shape> shape = new ArrayList<Shape>();;
public List<Shape> getShape() {
return shape;
}
public void setShape(List<Shape> shape) {
this.shape = shape;
}
}
方形
import javax.xml.bind.annotation.XmlAttribute;
public class Square extends Shape {
private String squareSpecificAttribute;
@XmlAttribute(name="square-specific-attribute")
public String getSquareSpecificAttribute() {
return squareSpecificAttribute;
}
public void setSquareSpecificAttribute(String s) {
this.squareSpecificAttribute = s;
}
}
三角形
import javax.xml.bind.annotation.XmlAttribute;
public class Triangle extends Shape {
private String triangleSpecificAttribute;
@XmlAttribute(name="triangle-specific-attribute")
public String getTriangleSpecificAttribute() {
return triangleSpecificAttribute;
}
public void setTriangleSpecificAttribute(String t) {
this.triangleSpecificAttribute = t;
}
}
下面是一个演示程序，用于检查一切是否正常:
Below is a demo program to check that everything works:
import java.io.StringReader;
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 jaxbContext = JAXBContext.newInstance(Shapes.class, Triangle.class, Square.class);
StringReader xml = new StringReader("<shapes><shape square-specific-attribute='square stuff' type='square'><points>4</points></shape><shape triangle-specific-attribute='triangle stuff' type='triangle'><points>3</points></shape></shapes>");
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
Shapes root = (Shapes) unmarshaller.unmarshal(xml);
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(root, System.out);
}
}
我希望这会有所帮助.
有关 EclipseLink MOXy 的更多信息，请参阅:
For more information on EclipseLink MOXy see:
编辑
在 EclipseLink 2.2 中，我们使其更易于配置，请查看以下文章了解更多信息:
In EclipseLink 2.2 we're making this easier to configure, check out the following article for more information:
这篇关于Java/JAXB:根据属性将 Xml 解组为特定子类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！