Current area: HOME -> Discover ISAPI. Feed provider for graphical applets
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Introduction
Some time ago I implemented a data feed system from SQL database to some
graphical applets.
At the beginning we decided a normal ASP script who read data and give it to
that applets will be usefully. Unfortunately wasn't !
The web server was crashed every time the number of simultaneous users on the site was bigger
like 80-100 and when an user tried to get bigger data in an applet.
For
that reasons we decided to move the feed on the ISAPI dll.
Advantages
- the ASP server is freed by the calls from clients applets. In that
way the asp will respond only to the normal site calls;
the asp will dont produce any time aout caused
by applets calls.
- keeping of connection to DB in the ISAPI cache, in that
way all request against DB will don't loose time with open connection,
will
use that public open connection variable (CAdoDatabase m_AdoDB).
- ISAPI extension dll are the best choice if you want to obtain the maximum
number of simultaneous connection to IIS web
server or to provide huge
quantities of HTML data.
Functionality
The ASP script load the applet class and give it some
parameters, like colors, time interval of http's requests,
web application URL,
etc.
<applet codebase="../AspDemoFeed/Tools/OnlineScroll/CLASSES/JavaScroller/"
archive="../AspDemoFeed/Tools/OnlineScroll/Scroller.jar" code="ScrollerStartUp.class" width="600"
height="20" VIEWASTEXT id="Scroller">
param name="speed" value="3"
param name="bgcolor" value="696969"
param name="Font" value="Arial|1|16"
param name="changeFontSize" value="11"
param name= "feedURL"value="<%=Application("WebURL")%>cgi-bin/IsapiDemoFeed.dll?GetOnlineScrollerData?"
param name="updateInterval" value="20000"</applet>
The java applet will made from the clients side to web
server HTTP requests at the received web URL parameter. That request
are maded
at equal interval of times give in milliseconds by "updateInterval" parameter.
If will open the java console on the client
will see some messages like:
Loading data from
http://localhost/projects/Articles/AspDemoFeed/cgi-bin/IsapiDemoFeed.dll?GetOnlineScrollerData?0&4
The ISAPI module respond to that HTTP hit with a know by
applet format, html stream:
0|2232160|453.4|2|14:19:06
1|576920|139.1|1|14:19:06
2|4006410|796.8|4|14:19:06
3|2511860|-31.5|2|14:19:06
4|2478810|529.2|0|14:19:06
At each HTTP hit, the ISAPI module make request again SQL
database, using the CAdoDatabase and
CAdoRecordset classes
from CodeProject site :).
The minor modification was the keep only database connection as public
variable.
On each method the record sets needed are open and close. An
optimization is the using of GetString
method of AdoRecordset class, who return directly a formatted data text.
Because the ISAPI dll is harder to debug, more attention must be to the errors
capture, resolved with try/catch macros.
try
{ CAdoRecordset* AdoRS = new CAdoRecordset; //create a recordset variable
if ( DBConnectionOpen( m_bstrConnectionString ) ) //look at db connection to be online
{ //open the recordset
if ( AdoRS->Open(m_AdoDB.GetActiveConnection(), bstrSTMT, adOpenForwardOnly,
adLockReadOnly, adUseClient ) ) //here the disc params
{ if(!AdoRS->IsEof()) //look if we have records
varOutput = AdoRS->GetString("|", "\n", 0 );
else
varOutput = "0 0 0 0 0 ";
AdoRS->Close(); //close the recordset
if (AdoRS) delete AdoRS;
}else //set the custom error
{ wsprintf(wcOut,"Encountered Error:<br>%s<br>%s<br>%s<br>%s<br>","MyFunction"
(LPCTSTR)m_AdoDB.GetLastError(), "RS isnt open", bstrSTMT );
*pCtxt << wcOut ; return;
}
}else //set the custom error
{ wsprintf(wcOut, "Encountered Error:<br>%s<br>%s<br>%s<br>%s<br>","GetMarketMapData",
(LPCTSTR)m_AdoDB.GetLastError(), "DB isn't open", bstrSTMT );
*pCtxt << wcOut ; return;
}
}
catch(_com_error err)
{ wsprintf(wcOut, "Encountered Error :<br>%s<br>%d<br>%s<br>", (LPSTR)err.Description(),
err.Error(), (LPSTR)err.ErrorMessage() );
*pCtxt << wcOut ; return;
}
*pCtxt << varOutput; //here the output
!!!
To test the feed, must make updates on the values of
tblOnline* tables.
That updating will be online reflected instantaneous to the Online tables and scrolling applets.
To see how is working Intraday charts applets make inserts in
tblIntraday* tables. Thats applets look permanently at thats tables and
updates our values in cells and points on the charts.
Install
- The ASP connection string are located in the Includes\_incConnectionOn.asp
file.
cnx.Provider = "sqloledb"
cnx.Open "Data Source=andi;Initial Catalog=ArticlesIsapiFeed;", "sa", ""
- The ISAPI connection string are located in IsapiDemoFeed.cpp file, on the
constructor:
m_bstrConnectionString="Provider=SQLOLEDB;Data Source=andi;Initial Catalog=ArticlesIsapiFeed;
UserID=sa;Password=;";
- Copy the folder "AspDemoFeed" under
your web site and make it ASP application, to work the session and
application ASP objects.
- Give "Scripts and Executables" Execute Permision
to "cgi-bin" directory of "AspDemoFeed"
web application.
In that way the ISS web server will be able to execute the
IsapiDemoFeed.dll.
- To install the database on your SQL server select restore database option
on SQL Server Enterprise Manager and choose
the "DB/ArticlesIsapiFeed.bak"
file backup. The name of database is
ArticlesIsapiFeed.
About Adrian Bacaianu
I make programming for over 4 years and extensive experience in C++, ASP, Pascal, MFC, COM+, ATL, TCP/IP, HTTP protocols, XML, XSL, SOAP and SQL.
For the last 2 years i working extensively at the background of financial sites (databases, n tier architecture).
I’m available for contracts and/or outsourcing. Contact adrian_bacaianu@yahoo.com.
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