JAVA/Android how to send XML with org.simpleframework.xml to a php Server

i would like to send XML Data to a PHP Webserver. I found the org.simpleframework.xml useful for that. What i have is a List of DayItem's like this:

public class DayItem{

    private int                         ID;
    private Date                        myDate;
    private boolean                     activeUserIsOnThatDay   = false;
    private boolean                     anAlertIsOnThatDay      = false;
...
}   

So how i can get this to a XML String WITHOUT writing it to a File on my Android Phone? Or is the only Way write this to a File an then send this??

Thank you so much