Ajax upload file in java

[regent_royal]

Hello, I want to use ajax upload I m using "commons-fileupload.jar" for uploading file... and below code is used to call servlet through ajax. Actually I am new in ajax so I can't understand what happens while I use multipart request.

My javascript is

<script language="javascript">
	
	function getXMLObject()  //XML OBJECT
	{
   		var xmlHttp = false;
	    try {
     		xmlHttp = new ActiveXObject("Msxml2.XMLHTTP")  // For Old Microsoft Browsers
   		}
   		catch (e) {
     		try {
       			xmlHttp = new ActiveXObject("Microsoft.XMLHTTP")  // For Microsoft IE 6.0+
     		}
     		catch (e2) {
       			xmlHttp = false   // No Browser accepts the XMLHTTP Object then false
     		}
   		}
   		if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
     		xmlHttp = new XMLHttpRequest();        //For Mozilla, Opera Browsers
   		}
   		return xmlHttp;  // Mandatory Statement returning the ajax object created
	}
 
var xmlhttp = new getXMLObject();	//xmlhttp holds the ajax object
 
	function addPhoto(){
		alert("before if");
		var f = document.form1.file;
		alert(f);
		alert(f1.value);
  		if(xmlhttp) { 
			alert("inside if");
  			xmlhttp.open("GET","ajaxUploadGenerator?file="+f,true); //ajaxUploadGeneratoris servlet name
			xmlhttp.onreadystatechange  = handleServerResponse;
			xmlhttp.setRequestHeader('Content-Type','multipart/form-data');
    		xmlhttp.send(null);
  		}
		alert("after if");
	}

	function handleServerResponse() {
   		if (xmlhttp.readyState == 4) {
     		if(xmlhttp.status == 200) {
    	 		document.getElementById("reply").innerHTML = xmlhttp.responseText;
     		}
     		else {
        		alert("Error during AJAX call. Please try again");
     		}
   		}
	}

</script>

and My page contains...

<form id="form1" name="form1" enctype="multipart/form-data">
  <label>
  <input type="file" name="file" />
  </label>
  <p>
    <label>
    <input type="button" name="Submit" value="Submit" onclick="addPhoto()"/>
	<div id="reply"></div>
    </label>
  </p>
  <iframe name="iframe" id="iframe" style="display:none">
  </iframe>
</form>