Question

假设我有

class Student
{
String name;
int    age;
String teacher;
}

然后：

public class App1
{
    public static void main(String[] args)
    {
        Student st = new Student();
        st.setName("toto");

        XStream xs = new XStream();

        xs.alias("student",Student.class);

        System.out.println(xs.toXML(st));
    }

}

给我：

<student>
  <name>toto</name>
  <age>0</age>
</student>

有没有办法处理空值？我的意思是：

<student>
  <name>toto</name>
  <age>0</age>
  <teacher></teacher>
</student>

我可以这样做

st.setTeacher("");

但如果老师为空则不行。

我尝试使用自定义转换器，但似乎空值不会发送到转换器。

Answer 1

我使用XStream 1.4.7，@ XStreamAlias注释用于自定义字段名称，@ XStreamConverter用于自定义转换器（用于表示日期和其他自定义bean）。但是，甚至没有调用空值的自定义转换器。我的目标是序列化对象的所有字段，包括空字段，我不需要解组XML。

我设法通过创建自定义ReflectionConverter来做到这一点。我从XStream库扩展了ReflectionConverter并覆盖了doMarshal方法。我唯一改变的是为null info.values调用writeField方法：

new Object() {
{
    for (Iterator fieldIter = fields.iterator(); fieldIter.hasNext();) {
        FieldInfo info = (FieldInfo) fieldIter.next();
        if (info.value != null) {
            //leave the code unchanged
            ...
        } else {
            //add this to write null info.value to xml
            Log.info("MyCustomReflectionConverter -> serialize null field: " + info.fieldName);
            writeField(info.fieldName, null, info.type, info.definedIn, info.value);
        }
    }
    //... leave the rest of the code unchanged
}
};

之后，我创建了类似的xStream实例（以非常低的优先级注册转换器非常重要）：

StaxDriver driver = new StaxDriver(new NoNameCoder()) {
    @Override
    public StaxWriter createStaxWriter(XMLStreamWriter out) throws XMLStreamException {
        // the boolean parameter controls the production of XML declaration
        return createStaxWriter(out, false);
    }
};

XStream xStream = new XStream(driver);
xStream.autodetectAnnotations(true);//needed to process aliases
//register MyCustomReflectionConverter
MyCustomReflectionConverter reflectionConverter = new MyCustomReflectionConverter (xStream.getMapper(), new SunUnsafeReflectionProvider());
xStream.registerConverter(reflectionConverter, XStream.PRIORITY_VERY_LOW);

感谢Mark Nabours的解决方案here

希望它有所帮助。有人找到了更好的解决方案吗？

Answer 2

首先在Student类中提供getter和setter方法，如下所示：

public class Student{
   String name;
   int age;
   String teacher;
   public void setName(String name){
       this.name = name;
   }
   public String getName(){
      return name;
   }
.......
......//Like that mention other getter and setter method
}

现在，您需要创建转换器类，如下所示：

public class StudentConverter implements Converter{
    public boolean canConvert(Class clazz) {
         return clazz.equals(Test.class);
    }
    public void marshal(Object value, HierarchicalStreamWriter writer,
         MarshallingContext context) {
       Student student = (Student ) value;
       writer.startNode("name");
       writer.setValue(test.getName());
       writer.endNode();
       writer.startNode("age");
       writer.setValue(test.getAge());
       writer.endNode();
       writer.startNode("teacher");
       writer.setValue("");
       writer.endNode();
   }
    public Object unmarshal(HierarchicalStreamReader reader,
         UnmarshallingContext context) {
       Student student = new Student();
       test.setName(reader.getNodeName());
       test.setAge(reader.getNodeName());
       test.setTeacher(reader.getNodeName());
       return student;
    }
}

Your main class will the like that:

public class App1{
    public static void main(String args[]) {
        XStream stream = new XStream(new StaxDriver());
        Student st = new Student();
        st.setName("ABC");
        t.setAge(21);
        stream.registerConverter(new StudentConverter());
        stream.alias("student", Student.class);
        System.out.println(stream.toXML(st));
   }

}

希望这是你的答案......快乐学习：）

Answer 3

你可以放一个空字符串

String teacher = StringUtils.EMPTY;

或优化一个：）

{{1}}

XStream序列化空值

3 个答案: