JSP code

Hi!
Can somebody provide a line by line explanation of the following code. The code is used to upload and download an image.

<%@ page import="java.io.*" %>
<%@ page import="java.sql.*" %>

<%
String saveFile="";
String contentType = request.getContentType();
if ((contentType != null) && (contentType.indexOf("multipart/form-data") >= 0)) {
DataInputStream in = new DataInputStream(request.getInputStream());
int formDataLength = request.getContentLength();
byte dataBytes[] = new byte[formDataLength];
int byteRead = 0;
int totalBytesRead = 0;
while (totalBytesRead < formDataLength) {
byteRead = in.read(dataBytes, totalBytesRead,formDataLength);
totalBytesRead += byteRead;
}
String file = new String(dataBytes);
saveFile = file.substring(file.indexOf("filename=\"") + 10);
saveFile = saveFile.substring(0, saveFile.indexOf("\n"));
saveFile = saveFile.substring(saveFile.lastIndexOf("\\") + 1,saveFile.indexOf("\""));
int lastIndex = contentType.lastIndexOf("=");
String boundary = contentType.substring(lastIndex + 1,contentType.length());
int pos;
pos = file.indexOf("filename=\"");
pos = file.indexOf("\n", pos) + 1;
pos = file.indexOf("\n", pos) + 1;
pos = file.indexOf("\n", pos) + 1;
int boundaryLocation = file.indexOf(boundary, pos) - 4;
int startPos = ((file.substring(0, pos)).getBytes()).length;
int endPos = ((file.substring(0, boundaryLocation)).getBytes()).length;
saveFile="C:/"+saveFile;
File f = new File(saveFile);
FileOutputStream fileOut = new FileOutputStream(f);
fileOut.write(dataBytes, startPos, (endPos - startPos));
fileOut.flush();
fileOut.close();
%><Br><table border="2"><tr><td><b>You have successfully upload the file by the name of:</b>
<% out.println(saveFile);%></td></tr></table>
<%
}
%>
<a href="download.jsp?f=<%=saveFile%>">Download</a>


/*Code to download an image*/
<%@ page import="java.util.*,java.io.*"%>
<%@ page import="java.net.*"%>
<%!
public static String getMimeType(String fileUrl)
throws java.io.IOException, MalformedURLException
{
String type = null;
URL u = new URL(fileUrl);
URLConnection uc = null;
uc = u.openConnection();
type = uc.getContentType();
return type;
}

%>
<%
String file=request.getParameter("f");
File f = new File (file);
String filename=f.getName();
String type=getMimeType("file:"+file);

response.setContentType (type);
response.setHeader ("Content-Disposition", "attachment; filename=\""+filename+"\"");

String name = f.getName().substring(f.getName().lastIndexOf("/") + 1,f.getName().length());
InputStream in = new FileInputStream(f);
ServletOutputStream outs = response.getOutputStream();

int bit = 256;
int i = 0;
try {
while ((bit) >= 0) {
bit = in.read();
outs.write(bit);
}
} catch (IOException ioe) {
ioe.printStackTrace(System.out);
}
outs.flush();
outs.close();
in.close();
%>