Create xml file using SSJS

Question 1

There are quite some ways. The seemingly easiest one is to create a string that looks like XML.

The next one would be the use of Java DOM classes. There is an article describing it.

Finally you can use SAX with a little helper class

Let us know how it goes.

Update: This would be my version of @Michael's code sample:

<?xml version="1.0" encoding="UTF-8"?>
<!-- XPage which is not rendered but returns data like XML, JSON, etc.     -->
<!-- More: http://www.wissel.net/blog/d6plinks/shwl-7mgfbn                 -->

<xp:view xmlns:xp="http://www.ibm.com/xsp/core" rendered="false">
    <xp:this.beforeRenderResponse><![CDATA[#{javascript:try {
    var out = facesContext.getOutputStream();
    var exCon = facesContext.getExternalContext();
    var response = exCon.getResponse(); // get the response context
    // set content type, e.g. ...
    response.setContentType("text/xml"); 
    // set caching option 
    response.setHeader("Cache-Control", "no-cache");
    // write XML output ...
    var result = new biz.taoconsulting.xmltools.SimpleXMLDoc();
    result.setOut(out);
    result.openTag("result");
    result.dateTag("created", new java.util.Date());
    result.addSimpleTag("Author",@UserName);
    result.openTag("FruitList");
    result.addComment("Stephan really likes the fruits example");
    var attributes = new java.util.HashMap();
    attributes.add("name","Durian");
    attributes.add("color","white");
    attributes.add("taste","Don't ask");
    result.addEmptyTag("fruit",attributes);
    result.closeDocument();
    // close the output
    exCon.responseComplete();
    out.close();
} catch (e) {
    print(e.toString());
}}]]>
    </xp:this.beforeRenderResponse>
</xp:view>

Note the differences here:

I use the beforeRenderResponse event
Access to outputStream instead of writer (stream is not accessible in the afterRenderResponse event)
set the response complete to stop the page from further output, so you can simply type comments on the page what it does
use of the helper class

What seems a little odd when you read the source of the helper class: why not use the output stream in the constructor, so you won't miss it? - I would today add a second constructor with that, but the parameterless constructor allow me to define that class as a managed bean if I fancy that.

Question 2

to "render" XML in a String as @Stefan suggested I would use the XAgent approach:

<?xml version="1.0" encoding="UTF-8"?>
<!-- XPage which is not rendered but returns data like XML, JSON, etc.     -->
<!-- More: http://www.wissel.net/blog/d6plinks/shwl-7mgfbn                 -->

<xp:view xmlns:xp="http://www.ibm.com/xsp/core" rendered="false">
    <xp:this.afterRenderResponse><![CDATA[#{javascript:try {
    var writer = facesContext.getResponseWriter(), // get a writer object 
        response = facesContext.getExternalContext().getResponse(); // get the response context
    // set content type, e.g. ...
    response.setContentType("text/xml"); 
    // set caching option 
    response.setHeader("Cache-Control", "no-cache");
    // write XML output ...
    writer.write(
        '<?xml version="1.0"?>\n'
        + '<root>\n'
        + '<entity>Example Content</entity>\n'
        + '</root>\n'
    );
    // close the stream
    writer.endDocument();
} catch (e) {
    print(e.toString());
}}]]>
    </xp:this.afterRenderResponse>
    <xp:this.resources>
        <xp:script src="/XBAN.jss" clientSide="false"></xp:script>
    </xp:this.resources>
</xp:view>

Simply put his code into a newly created XPage and test it. Modify the lines in writer.write() to fit to your needs.