<apex:page controller="Xmlretrive" >
    <apex:form >
    <script type="text/javascript">
      function doSearch() {
        searchServer(
          document.getElementById("s1").value,
          document.getElementById("s2").value,
          document.getElementById("s3").value,
          );
      }
     </script>
         
    <apex:actionFunction name="searchServer" action="{!getXml}" rerender="output,resoutput" >
          <apex:param name="s1" value="" />
          <apex:param name="s1" value="" />
          <apex:param name="s1" value="" />         
      </apex:actionFunction>
        <apex:pageBlock >
            <apex:pageBlockButtons location="top">
                <apex:commandButton value="Click here to submit" action="{!submit}" reRender="output,resoutput" />
                       
            </apex:pageBlockButtons>
            <apex:pageBlockSection columns="1">
                <Apex:pageBlockSectionItem >
                    <apex:outputLabel >Enter the username :</apex:outputLabel>
                    <apex:inputText id="s1" value="{!userName}" />
                </Apex:pageBlockSectionItem>
                <apex:pageBlockSectionItem >
                    <apex:outputLabel >Password :</apex:outputLabel>
                    <apex:inputSecret id="s2" value="{!password}" />
                </apex:pageBlockSectionItem>
                <apex:pageBlockSectionItem >
                    <apex:outputLabel >Oauth URL</apex:outputLabel>
                    <apex:inputText id="s3" value="{!auth}" />
                </apex:pageBlockSectionItem>
            </apex:pageBlockSection>
        </apex:pageBlock>
----------------------
public class Xmlretrive {
  
     public String Xml{
        get;
        set;
    }
   
    public String xmlOutput {
        get;
        set;
    }
    String simple = 'bharath';

    public String auth {
        get;
        set;
    }
    public String password {
        get;
        set;
    }
    public String userName {
        get;
        set;
    }
    public boolean displayxml {
        get;
        set;
    }
    public Xmlretrive() {
        displayxml = false;
  
    }
    public PageReference submit( ) {
        displayxml = true;
        getXml(userName,password,auth );
        if (userName == null) {
            userName = 'Write here';
        } else {
            userName = userName;
            password = password;
            auth = auth;
        }
        return null;
    }
    public PageReference getXml() {
        String userName = Apexpages.currentPage().getParameters().get('s1');
        String password = Apexpages.currentPage().getParameters().get('s2');
        String auth = Apexpages.currentPage().getParameters().get('s3');
              
        XmlStreamWriter w = new XmlStreamWriter();
        w.writeStartDocument(null, '1.0');
        w.writeProcessingInstruction('target', 'data');
        w.writeStartElement('', 'attrs','http://www.sap.com/rws/bip');
        w.writeNamespace('', 'http://www.sap.com/rws/bip' );
        w.writeStartElement('', 'attr', 'http://www.sap.com/rws/bip' );
        w.writeAttribute(null, null,'name', 'username');
        w.writeAttribute(null, null,'type', 'string');
        w.writeCharacters(username);
        w.writeEndElement();
        w.writeStartElement('', 'attr', 'http://www.sap.com/rws/bip' );
        w.writeAttribute(null, null, 'name', 'password');
        w.writeCharacters(password);
        w.writeEndElement();
        w.writeStartElement('', 'attr', 'http://www.sap.com/rws/bip' );
        w.writeAttribute(null, null,'name', 'auth');
        w.writeAttribute(null, null, 'type', 'string');
        w.writeAttribute(null, null,'possibilities','secEnterprise,secLDAP,secWinAD,secSAPR3' );
        w.writeCharacters(auth);
        w.writeEndElement();
        w.writeEndElement();
        w.writeEndDocument();
        String xmlOutput = w.getXmlString();
        w.close();
       
        //string test = ' <some xml format data>';
        // otherwise we hit a limit of 32000

       
        //System.debug(xmlOutput);
        return null;
    }