通过 JAXB 为枚举提供自定义值序列化 [英] Providing custom value serialization for enums via JAXB

问题描述

对于我正在处理的一个项目，我们使用了很多枚举.模型对象本身由许多小类组成；然后我们通过 JAXB 将此模型作为 XML 序列化到我们的数据库.现在，我们希望能够使用枚举中特定方法的返回来序列化我们的枚举值；给出的:

For a project I'm working on, we have a lot of enums in use. The model object itself is composed from a lot of tiny classes; this model we then serialize to our DB as XML via JAXB. Now, we want to be able to serialize our enum values using the return of a particular method in the enum; that is given:

public enum Qualifier {
    FOO("1E", "Foo type document"),
    BAR("2", "Bar object");

    private String code, description;

    public Qualifier(String code, String description) {
        this.code = code;
        this.description = description;
    }

    public String getCode() {
        return this.code;
    }

    public String getDescription() {
        return this.description;
    }
}

等等.等等.目前，当序列化为 XML 时，我们得到如下内容:

etc. etc. Currently, when serialized to XML, we get something like:

<qualifier>FOO</qualifier>

这就是 JAXB 处理它的方式.然而，我们需要该值是 getCode() 的返回值，并且我们的大量枚举确实遵循该约定(具有用于通过代码查找的相应静态方法)，因此上述 XML 片段如下所示:

which is how JAXB handles it. However, we need the value to be the return of getCode(), and a whole lot of our enums do follow that convention (with a corresponding static method for lookup via code), so that the above XML fragment looks like:

<qualifier>1E</qualifier>

相反.我们可以用@XmlEnum 和@XmlEnumValue 来注释它，但这太繁琐了——有些枚举最多有30 个枚举值，手工编辑也不好.我们也在考虑使用自定义序列化程序，但我现在不想走这条路(但如果这是要走的路，那么我没有问题).

instead. We can annotate it with @XmlEnum and @XmlEnumValue, but that's too tedious -- some enums have up to 30 enumerated values, and hand-editing it is not good. We're also thinking of using a custom serializer instead, but I'd like to avoid going that route for now (but if that's the way to go, then I have no problem with it).

有什么想法吗?

推荐答案

为此尝试使用 XmlAdapter 机制.您为每个枚举类型创建一个 XmlAdapter 子类，该子类知道如何将枚举编组/解组为 XML.

Try using the XmlAdapter mechanism for this. You create an XmlAdapter subclass for each enum type, and which knows how to marshal/unmarshal the enum to and from XML.

然后您将适配器与属性相关联，例如

You then associate the adapter with the property, e.g.

public class QualifierAdapter extends XmlAdapter<String, Qualifier> {

   public String marshal(Qualifier qualifier) {
      return qualifier.getCode();
   }

   public Qualifier unmarshal(String val) {
      return Qualifier.getFromCode(val);   // I assume you have a way of doing this
   }
}

然后在模型类中:

@XmlJavaTypeAdapter(QualifierAdapter.class)
private Qualifier qualifier;

您也可以在包级别声明这一点，在与模型类相同的包中的一个名为 package-info.java 的文件中，使用相当特殊的包注释:

You can also declare this at the package level, inside a file called package-info.java in the same package as your model classes, using the rather idiosyncratic package annotations:

@javax.xml.bind.annotation.adapters.XmlJavaTypeAdapters({
  @javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter(
    type=Qualifier.class, value=QualifierAdapter.class
  )
})
package com.xyz;

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