changing filename after uploading image

I am doing application where i am selecting img to be uploaded . after uploading i want to change its file name. to values that i am getting from session

example useridcompid.img save it.

a2) i want to saveimage in img folder using relative url

I am attaching my code below

[CODE]
<html>
<head>
<title>
Status...
</title>
<link href="forAll.css" rel="stylesheet" type="text/css">
<script type="text/javascript">
</script>
</head>
 
<body>
<%@ include file="LoginHeader.jsp" %>
 
<%
 
    response.setContentType("text/html");
    response.setHeader("Cache-control","no-cache");
   [B] String userid=(String)session.getAttribute("userID");
    String compid=(String)session.getAttribute("companyId");[/B]String err = "";
    String lastFileName = "";
    String contentType = request.getContentType();
    String boundary = "";
    final int BOUNDARY_WORD_SIZE = "boundary=".length();
    if(contentType == null || !contentType.startsWith("multipart/form-data")) {
      err = "Ilegal ENCTYPE : must be multipart/form-data\n";
      err += "ENCTYPE set = " + contentType;
    }else{
      boundary = contentType.substring(contentType.indexOf("boundary=") + BOUNDARY_WORD_SIZE);
      boundary = "--" + boundary;
      try {
        javax.servlet.ServletInputStream sis = request.getInputStream();
        byte[] b = new byte[1024];
        int x=0;
        int state=0;
        String name=null,fileName=null,contentType2=null;
        java.io.FileOutputStream buffer = null;
        while((x=sis.readLine(b,0,1024))>-1) {
          String s = new String(b,0,x);
          if(s.startsWith(boundary)) {
            state = 0;
            //out.println("name="+name+"<br>");
            //out.println(fileName+"<br>");
 
            name = null;
            contentType2 = null;
            fileName = null;
 
 
          }else if(s.startsWith("Content-Disposition") && state==0) {
            state = 1;
            if(s.indexOf("filename=") == -1)
              name = s.substring(s.indexOf("name=") + "name=".length(),s.length()-2);
            else {
              name = s.substring(s.indexOf("name=") + "name=".length(),s.lastIndexOf(";"));
              fileName = s.substring(s.indexOf("filename=") + "filename=".length(),s.length()-2);
              if(fileName.equals("\"\"")) {
                fileName = null;
              }else {
                String userAgent = request.getHeader("User-Agent");
                String userSeparator="/";  // default
                if (userAgent.indexOf("Windows")!=-1)
                  userSeparator="\\";
                if (userAgent.indexOf("Linux")!=-1)
                  userSeparator="/";
                fileName = fileName.substring(fileName.lastIndexOf(userSeparator)+1,fileName.length()-1);
                if(fileName.startsWith( "\""))
                  fileName = fileName.substring( 1);
              }
            }
            name = name.substring(1,name.length()-1);
            if (name.equals("file")) {
              if (buffer!=null)
                buffer.close();
              lastFileName = fileName;
            [B]  buffer = new java.io.FileOutputStream("/img/"+fileName);[/B]
            }
          }else if(s.startsWith("Content-Type") && state==1) {
            state = 2;
            contentType2 = s.substring(s.indexOf(":")+2,s.length()-2);
          }else if(s.equals("\r\n") && state != 3) {
            state = 3;
          }else {
            if (name.equals("file"))
              buffer.write(b,0,x);
          }
        }
        sis.close();
        buffer.close();
      }catch(java.io.IOException e) {
        err = e.toString();
      }
    }
    boolean ok = err.equals("");
    if(!ok) {
      out.println(err);
    }else{
    %>
<SCRIPT language="javascript">
  history.back(1)
  alert('Uploaded <%=lastFileName%>');
  window.location.reload(false)
</SCRIPT>
    <%
    }
    out.println("done");
%>
<%@ include file="Footer.jsp" %>
</body>
</html>

[/CODE]

i want to saveimage in img folder using relative url

You can't save image in a folder using relative path, you have to use absolute path.