使用XStream反序列化空的XML元素

Question

在我接收到的XML流中，有以下语句。

<user>
    <age/>
</user>

需要插入到类似于这样的对象中：

@XStreamAlias("user")
public class User {

    public int age = 0;
}

很不幸，每次我尝试阅读这个XML时，都会收到XStream异常，因为age xml标记为空：

Exception in thread "main" com.thoughtworks.xstream.converters.ConversionException: For input string: "" : For input string: ""
---- Debugging information ----
message             : For input string: ""
cause-exception     : java.lang.NumberFormatException
cause-message       : For input string: ""
class               : java.lang.Integer
required-type       : java.lang.Integer
converter-type      : com.thoughtworks.xstream.converters.SingleValueConverterWrapper
wrapped-converter   : com.thoughtworks.xstream.converters.basic.IntConverter
path                : /GoodreadsResponse/user/age
line number         : 17
class[1]            : fr.riduidel.exporter.goodreads.User
converter-type[1]   : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
class[2]            : fr.riduidel.exporter.goodreads.GoodreadsResponse
version             : null
-------------------------------
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshallField(AbstractReflectionConverter.java:355)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:306)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:234)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:322)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:234)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
    at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1052)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1036)
    at com.thoughtworks.xstream.XStream.fromXML(XStream.java:921)

我该如何告诉XStream将此字段视为“可选”或“可能不含任何内容”？

- Riduidel

Answer 1

很遗憾，这并不像我们想象的那么容易。你可以通过以下两种方式来实现：

• 编写一个XSLT转换，在使用XStream读取流之前将其应用于流中，以使XML与Java Beans匹配；或者
• 编写自己的JavaBeanConverter并将其注册到XStream中。这样，您可以详细定义如何将XML映射到Java Beans。您可以在此处找到如何在XStream上注册JavaBeanConverter的提示。

- Chris