以编程方式确定JAXB注释是否会导致xsi：type注释？ [英] Programmatically determine if a JAXB annotation will result in a xsi:type annotation?

问题描述

反思JAXB带注释的对象，有没有办法确定类/字段/方法是否会在编组期间产生xsi：type属性？

Reflecting on JAXB annotated objects, is there a way to determine if a class/field/method will result in a xsi:type attributed during marshaling?

是否为XmlElement注释，

annotation.type！= javax.xml.bind.annotation.XmlElement.DEFAULT.class

唯一的案例我需要担心吗？

Is XmlElement annotation,
annotation.type != javax.xml.bind.annotation.XmlElement.DEFAULT.class
the only case I need to worry about?

我正在写一个Lua unmarshaler，我们已经删除了大部分通常的xml类型信息，我正在试图弄清楚如何将传入的Lua与JAXB匹配。

I'm writing a Lua unmarshaler where we have dropped much of the usual xml type info and I'm trying to figure-out how to match the incoming Lua to JAXB.

谢谢。

- 更新 -

以下是显示问题的简单示例：

Here is simple example that shows the problem:

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
@XmlSeeAlso({ Cat.class, Dog.class })
public class Animal {
  @XmlElement()
  public List<Animal> critters;
  @XmlAttribute
  public String type;
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
public class Dog extends Animal {
  public Dog() {
    this.type = "German Shepherd";
  }
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
public class Cat extends Animal {
  public Cat() {
    this.type = "Black";
  }
}

当我收到Animal对象时，我可以查询生物的注释检测它应该是狗还是猫而不是动物？

When I receive an Animal object can I query critter's annotation to detect that it should be a Dog or Cat and not an Animal?

推荐答案

有几种情况下 JAXB（JSR-222） 实现将写出xsi：类型属性。

There are a couple circumstances where a JAXB (JSR-222) implementation will write out an xsi:type attribute.

1. 如果字段/属性的类型为对象（或者是用 @XmlElement（type = Object.class）注释并且没有用 @XmlAnyElement（lax = true）映射并保存一个Object的实例 JAXBContext`有映射。


2. 表示继承的默认机制将导致 xsi：type 属性表示子类（请参阅： http：// blog .bdoughan.com / 2010/11 / JAXB和继承-USI NG-xsitype.html ）。

1. If the field/property is of type Object (or is annotated with @XmlElement(type=Object.class)) and not mapped with@XmlAnyElement(lax=true)and holds an instance of an Object that theJAXBContext` has mappings for.
2. The default mechanism for representing inheritance will result in an xsi:type attribute to represent subclasses (see: http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-xsitype.html).

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