如何使用XStream有条件地序列化字段(属性)

Question

我正在使用XStream来序列化和反序列化对象.例如,一个名为的类Rating定义如下:

Public Class Rating {

  String id;
  int score;
  int confidence;

  // constructors here...
}

但是,在此类中,变量confidence是可选的.

因此,当置信度值(非0)时,Rating对象的XML表示应如下所示:

<rating>
<id>0123</id>
<score>5</score>
<confidence>10</confidence>
</rating>

但是,当置信度未知(默认值为0)时,应从XML表示中省略置信属性:

<rating>
<id>0123</id>
<score>5</score>
</rating>

谁能告诉我如何使用XStream有条件地序列化字段？

Answer 1

一种选择是编写转换器.

这是我很快为你写的:

import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;

public class RatingConverter implements Converter
{

    @Override
    public boolean canConvert(Class clazz) {
        return clazz.equals(Rating.class);
    }

    @Override
    public void marshal(Object value, HierarchicalStreamWriter writer,
            MarshallingContext context) 
    {
        Rating rating = (Rating) value;

        // Write id
        writer.startNode("id");
        writer.setValue(rating.getId());
        writer.endNode();

        // Write score
        writer.startNode("score");
        writer.setValue(Integer.toString(rating.getScore()));
        writer.endNode();

        // Write confidence
        if(rating.getConfidence() != 0)
        {
            writer.startNode("confidence");
            writer.setValue(Integer.toString(rating.getConfidence()));
            writer.endNode();
        }
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader arg0,
            UnmarshallingContext arg1)
    {
        return null;
    }
}

剩下的就是注册转换器,并在Rating类中提供访问器方法(即getId,getScore,getConfidence).

注意:您的另一个选择是适当地省略该字段.