Selon les ressources ci dessous, on peut rajouter la classe MarshalDouble :

package org.ksoap2.serialization;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlSerializer;

import java.io.IOException;

public class MarshalDouble implements Marshal {

    public Object readInstance(XmlPullParser parser, String namespace, String name, PropertyInfo expected)
            throws IOException, XmlPullParserException {
        return Double.parseDouble(parser.nextText());
    }

    public void writeInstance(XmlSerializer writer, Object obj) throws IOException {
        writer.text(obj.toString());
    }

    public void register(SoapSerializationEnvelope cm) {
        cm.addMapping(cm.xsd, "double", Double.class, this);

    }

}

Et l'utiliser lors de l'appel à notre WS :

SoapSerializationEnvelope soapEnvelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
        soapEnvelope.implicitTypes = true;
        soapEnvelope.dotNet = true;

        MarshalDouble md = new MarshalDouble();
        md.register(soapEnvelope );

Mais étant donné que nous avons déjà créé un MarshalFloat, qui traite les float, double et decimal, dans le package org.ksoap2.serialization au lieu d'ajouter MarshalDouble, on peut utiliser notre MarshalFloat :

SoapSerializationEnvelope soapEnvelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
        soapEnvelope.implicitTypes = true;
        soapEnvelope.dotNet = true;

        MarshalFloat md = new MarshalFloat();
        md.register(soapEnvelope);

Déclaration de notre MarshalFloat qui sérialise les types : float, double et decimal, :

package org.ksoap2.serialization;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlSerializer;

import java.io.IOException;

public class MarshalFloat implements Marshal {

    public Object readInstance(XmlPullParser parser, String namespace, String name, PropertyInfo propertyInfo)
            throws IOException, XmlPullParserException {
        String stringValue = parser.nextText();
        Object result;
        if (name.equals("float")) {
            result = new Float(stringValue);
        } else if (name.equals("double")) {
            result = new Double(stringValue);
        } else if (name.equals("decimal")) {
            result = new java.math.BigDecimal(stringValue);
        } else {
            throw new RuntimeException("float, double, or decimal expected");
        }
        return result;
    }

    public void writeInstance(XmlSerializer writer, Object instance) throws IOException {
        writer.text(instance.toString());
    }

    public void register(SoapSerializationEnvelope cm) {
        cm.addMapping(cm.xsd, "float", Float.class, this);
        cm.addMapping(cm.xsd, "double", Double.class, this);
        cm.addMapping(cm.xsd, "decimal", java.math.BigDecimal.class, this);
    }
}

Ressources :