Re: converting some VB code to Java..

From:
Frances <fdr58@yahoo.com>
Newsgroups:
comp.lang.java.help
Date:
Tue, 30 May 2006 14:38:41 -0400
Message-ID:
<447c9112$0$15795$14726298@news.sunsite.dk>
actually, the db-code you sent, I did know how to do that.. I had just
thought that for AJAX it had to be diff. code from usual.. it's wild
how this works, results print right on page that sends the request, yet
when you go to view generated HTML code the result that appears on the
page is not there.. I know it's pulled with this code:

    document.getElementById(<divId>).innerHTML=xmlHttp.responseText

but still don't know how this transfers results from JSP page to client
page.. this is very intriguing stuff...

many thanks again..

Bjorn Abelli wrote:

"maya" <fdr58@yahoo.com> wrote...

Bjorn Abelli wrote:

A simple Google gives plenty of sites with AJAX connected to Java:

http://tinyurl.com/pmypd

Why not from the horses mouth, Sun:

http://developers.sun.com/ajax/

Plenty of examples there... ;-)


thank you Bjorn, I HAD searched in Google, and had found some stuff (among
others sun-pg you mention above) but can't find a step-by-step java-based
tutorial like the one here..
http://www.w3schools.com/ajax/default.asp

since you seem to know about AJAX I was wondering,


Actually, I had only heard of it, but never used it, before you asked for
it... ;-)

am looking for AJAX 'docs'...


I don't think anyone "owns" the concept. That would be Adaptive Path who
coined the expression:

http://www.adaptivepath.com/publications/essays/archives/000385.php

closest thing I found is here...
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/xmlsdk/html/7924f6be-c035-411f-acd2-79de7a711b38.asp

why does XMLHTTPRequest have an "I" at the beginning here? (it's referred
to as "IXMLHTTPRequest")


Microsoft has a naming standard where interfaces "always" starts with an
"I".

That IXMLHTTPRequest is not "exactly" the same as XMLHTTPRequest, but as it
started in IE, MSDN is one source:

http://tinyurl.com/n8n7p

Other pages that explain the concepts are:

http://en.wikipedia.org/wiki/XMLHttpRequest
http://www.xulplanet.com/references/objref/XMLHttpRequest.html
http://developer.mozilla.org/en/docs/AJAX:Getting_Started
http://developer.apple.com/internet/webcontent/xmlhttpreq.html

I would like to know what all the objs are that these properties & methods
can be applied to (is XMLHttpRequest the only obj here? or are there
others? I just need to get the "big picture" here....:)

So I'd suggest you get your hands dirty with JDBC, ResultSets,
PreparedStatements, etc... ;-)


I do know how to do db-stuff w/Java, Bjorn (probably not as much as you
do, but I do know how to connect to db, insert stuff into tables, do
updates and queries, etc..) right now I just need to figure out how to do
this in java:

 response.write("<table>")
 do until rs.EOF
   for each x in rs.Fields
     response.write("<tr><td><b>" & x.name & "</b></td>")
     response.write("<td>" & x.value & "</td></tr>")
   next
   rs.MoveNext
 loop

rs.EOF?? (resultSet EndOfFile? what does this mean?)


Yes, ADO has a slightly different approach than JDBC... ;-)

Other than that, the code would look quite similar, e.g.:

  out.print("<table>");

  while (rs.next ())
  {
     for (int i = 0; i < columnCount; i++)
     {
         out.print(
             "<tr><td><b>" +
              rsMetaData.getColumnName(i+1) +
              "</b></td>");
         out.print(
             "<td>" +
             rs.getString (i+1) +
             "</td></tr>");
      }
   }

...should be corresponding to the code you extracted.

ok, no more on AJAX questions (unless it's an AJAX/Java-related
question....:), since this is not an AJAX group.. have more JS/AJAX code
questions (xmlHttp.readyState=="complete" -- what is "complete"..), I
guess I need to switch to JS ng (I guess no AJAX-ng yet..)


Yep, that's on the client side...

again, many thanks for yr help..


You're welcome.

// Bjorn A

---------------------------------
Appendix
---------------------------------
The servlet, not tested though...

import java.sql.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class AjaxDatabaseServlet extends HttpServlet
{
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
                      throws ServletException, IOException
    {
        PrintWriter out = response.getWriter();

        String sql =
           "SELECT * FROM CUSTOMERS WHERE CUSTOMERID=" +
            request.getParameter("q");

        // You might want to fix the path to the database

        String url =
            "jdbc:odbc:DRIVER={Microsoft Access Driver (*.mdb)};DBQ=" +
            "/db/northwind.mdb";

        try
        {
            DriverManager.registerDriver(
               new sun.jdbc.odbc.JdbcOdbcDriver());

            Connection conn = DriverManager.getConnection (url);
            Statement stmt = conn.createStatement ();
            ResultSet rs = stmt.executeQuery (sql);
            ResultSetMetaData rsMetaData = rs.getMetaData();

            int columnCount = rsMetaData.getColumnCount();

            out.print("<table>");

            while (rs.next ())
            {
                for (int i = 0; i < columnCount; i++)
                {
                    out.print(
                        "<tr><td><b>" +
                        rsMetaData.getColumnName(i+1) +
                        "</b></td>");
                    out.print(
                        "<td>" +
                        rs.getString (i+1) +
                        "</td></tr>");

                }
            }

            out.print("</table>");

            // cleanup...

            rs.close();
            stmt.close();
            conn.close();
        }
        catch (SQLException ex)
        {
            ex.printStackTrace(out);
        }
    }
}

/// Bjorn A

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