Create xml temporary and send to WebService

Hello, I am trying to create a temporary xml file and send it to a web service (the WebService already has the parameter 'String xml' which is the one that receives it) I just do not understand how to make it temporary, I would appreciate your help also xml format is next:

<Entidad>
    <row>
        <Parametro1>a</Parametro1>
        <Parametro2>b</Parametro1>
    </row>
    <row>
        <Parametro1>x</Parametro1>
        <Parametro2>y</Parametro1>
    </row>
</Entidad>