问题描述
我想设置一个 JAXB 注释的 Java 类来生成以下格式的一些 XML:
I would like to setup a JAXB-annotated Java class to generate some XML in the following format:
<page refId="0001">
<title>The title of my page</title>
</page>
refId"字段是可选的,所以我想使用 Guava 的 Optional 构造来引用内存中的字符串.我看到 使用通用 @XmlJavaTypeAdapter 解组包装在 Guava 的 Optional 中,如果您使用的是元素(即使这不是最初的问题),但是您将如何为 XML 属性设置注释?
The "refId" field is optional, so I'd like to use Guava's Optional construct to reference the string in memory. I see Using generic @XmlJavaTypeAdapter to unmarshal wrapped in Guava's Optional, which gives a thorough example if you're using an element (even if that wasn't the original question), but how would you set up the annotations for an XML attribute?
这是我目前所拥有的:
@XmlRootElement(name="page")
public final class Page {
@XmlAttribute
@XmlJavaTypeAdapter(OptionalAdapter.class)
private Optional<String> refId;
@XmlElement
private String title;
... getters/setters, default constructor, etc.
}
而 OptionalAdapter 是一个简单的 XmlAdapter:
And OptionalAdapter is a simple XmlAdapter:
public class OptionalAdapter<T> extends XmlAdapter<T, Optional<T>> {
@Override
public Optional<T> unmarshal(T v) throws Exception {
return Optional.fromNullable(v);
}
@Override
public T marshal(Optional<T> v) throws Exception {
if (v == null || !v.isPresent()) {
return null;
} else {
return v.get();
}
}
}
当我尝试针对上述代码加载单元测试时,它在初始化期间立即失败,但是如果我将注释更改为@XmlElement,测试将运行并通过,但显然将 refId 设置为子元素一个属性.
When I try to load up a unit test against the above code, it fails instantly during initialization, but if I change the annotation to @XmlElement, the test will run and pass, but obviously sets the refId as a child element instead of an attribute.
提前致谢!
推荐答案
Xml-attribute 只能有简单类型(如 String
、Integer
等),所以你不能使用 OptionalAdapter
.
如果您的字段具有 String
类型,则适配器应具有 OptionalAdapter
类型.
您可以通过以下方式进行:
- 创建额外的类,使用为 XmlAdapter
Xml-attribute can have only simple type (like String
, Integer
etc.), so you cann't use OptionalAdapter<T>
.
If your field has type String
then adapter should have type OptionalAdapter<String>
.
You can do in next way:
- create additional class, and use is as XmlAdapter
public final class StringOptionalAdapter extends OptionalAdapter<String>
{
}
Page.java
@XmlAttribute
@XmlJavaTypeAdapter(StringOptionalAdapter.class)
private Optional<String> refId;
这篇关于将 Guava 的 Optional 与 @XmlAttribute 一起使用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!