Image uploading

Hi,can anyone explain the following code. The code related to uploading an image file to oracle database using java servlet.

CODE

import java.io.*; import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.util.List; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.disk.DiskFileItemFactory; import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class AddPhotoServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { // Apache Commons-Fileupload library classes DiskFileItemFactory factory = new DiskFileItemFactory(); ServletFileUpload sfu = new ServletFileUpload(factory);

        if (! ServletFileUpload.isMultipartContent(request)) {
            System.out.println("sorry. No file uploaded");
            return;
        }

        // parse request
        List items = sfu.parseRequest(request);
        FileItem  id = (FileItem) items.get(0);
        String photoid =  id.getString();
       /* String photoid=request.getParameter("id");*/
        FileItem title = (FileItem) items.get(1);
       String   phototitle =  title.getString();
           //String   phototitle = request.getParameter("title"); */
        // get uploaded file
       FileItem file = (FileItem) items.get(2);
              /*String s=request.getParameter("photo");
               File file=new File(s);    
               FileInputStream fin = new FileInputStream(file); */
        // Connect to Oracle
        Class.forName("oracle.jdbc.driver.OracleDriver");
        Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE", "scott", "tiger");
        con.setAutoCommit(false);

        PreparedStatement ps = con.prepareStatement("insert into photos values(?,?,?)");
        ps.setString(1, photoid);
        ps.setString(2, phototitle);
        // size must be converted to int otherwise it results in error
        ps.setBinaryStream(3, file.getInputStream(), (int) file.getSize());
        ps.executeUpdate();
        con.commit();
        con.close();
        out.println("Proto Added Successfully. <p> <a href='listphotos'>List Photos </a>");
    }
    catch(Exception ex) {
        out.println( "Error --> " + ex.getMessage());
    }
}

}

In the above code I want to know functionality of DiskFileItemFactory, ServletFileUpload and FileItem classes. please help me.Thank you.