Java – xStream serializes null values

Suppose I have

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

then:

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));
    }

}

Give me:

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

Is there any way to handle null values? Well, I mean:

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

If I do, maybe

st.setTeacher("");

But if the teacher is empty, then No

I try to use a custom converter, but it seems that null values will not be sent to the converter

Solution

I'm using xStream 1.4 7. The @ xstreamalias annotation is used for custom field names, and the @ xstreamconverter is used for custom converters (used to represent dates and other custom beans) However, there is not even a custom converter that calls null values

I try to do this by creating a custom reflectionconverter I extended reflectionconverter from the xStream library and overridden the domarshal method The only thing I changed was null info Values calls the writefield method:

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
}
};

After that, I created a similar xStream instance (it is important to register the converter with a very low priority):

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);

Thanks for mark nabours' solution here

I hope I can help you Has anyone found a better solution?