Hi Karthikeyan:
Different modeling techniques as well as how/when to connect to databases (esp.
with connection pools) have been discussed in this list a few times. So rather
than read my 2-cents worth, I think you may do well to look in the archives. Far
smarter people than me have said a lot more than I can hope to! (:-)
Good luck!
Geeta
karthikeyan wrote:
> Hi Geeta,
>
> I wonder which is best way to connect to database and get your job done.
>
> Right Now what i am doing is :
>
> JSP -> Bean -> Database
>
> Database ->Bean->JSP
>
> I am opening the connection in the Beans Constructor.
>
> Whether there is any flaw in this approach if not how best can i improve
> this model.
>
> With Regards,
>
> b.karthikeyan.
> ----- Original Message -----
> From: Geeta Ramani <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Wednesday, August 01, 2001 8:36 PM
> Subject: Re: Refresh servlet page problem
>
> >
> > Hi Andrew:
> >
> > I think this is your problem: you are opening your connection in the
> init()!
> > init() is executed *just* once at servlet initialization time and *not*
> every
> > time a person posts (or gets)! So what is happening is your connection is
> opened
> > at init(), closed after the first doGet() and further doGets() don't have
> > connection to work with (hence a null pointer exception). So this is what
> you
> > should do:
> > Create and close the connection in the doGet()/doPost() and I believe your
> > troubles will be over. (You would do well to create a connection pool in
> the
> > init() and then get and release connections from the pool, but that's
> another
> > story..)
> >
> > Geeta
> >
> > andrew tollin wrote:
> >
> > > Thank you Marco,
> > >
> > > I have attempted to close the statement along with the connection within
> the
> > > doGet method as follows:
> > > finally {
> > > file://close the database connection.
> > > try {
> > > if (stmt !=null) stmt.close();
> > > if (con !=null) con.close();
> > > }
> > > catch (SQLException e) {}
> > > }
> > >
> > > I open the connection in the init() method as follows. I dont quite
> > > understand what my problem is! Help
> > >
> > > public void init(ServletConfig config)
> > > throws ServletException
> > > {
> > > super.init(config);
> > > try {
> > > // Loads the driver
> > > Class.forName("org.gjt.mm.mysql.Driver");
> > >
> > > // Get a Connection to the database
> > > con = DriverManager.getConnection (url);
> > > }
> > > catch (Exception E) {
> > > System.err.println("Unable to load driver.");
> > > E.printStackTrace();
> > > } // end catch
> > >
> > > ----- Original Message -----
> > > From: "Marco Trevisan" <[EMAIL PROTECTED]>
> > > To: <[EMAIL PROTECTED]>
> > > Sent: Wednesday, August 01, 2001 9:36 AM
> > > Subject: Re: Refresh servlet page problem
> > >
> > > > Looks like the first time the servlet is invoked it works OK.
> > > > Subsequent invocations mess up the connection (never
> > > > worked on mysql but I'd close and reopen the connection
> > > > or better use a connection pooling package, maybe stmt
> > > > isn't being closed).
> > > > When you open via the address bar I suspect you get the
> > > > cached HTML produced the first time.
> > > >
> > > > Marco
> > > >
> > > > ----- Original Message -----
> > > > From: andrew tollin
> > > > To: [EMAIL PROTECTED]
> > > > Sent: Tuesday, July 31, 2001 10:14 PM
> > > > Subject: Refresh servlet page problem
> > > >
> > > >
> > > >
> > > > Hello
> > > >
> > > > I have a problem with my servlets. I have created a number of servlets
> > > that
> > > > connect to a database, access a particular table, and insert the
> database
> > > > information into skeletal HTML. When I view my page on Tomcat port
> > > > 8090(changed from port 8080 due to DB probs) by entering
> > > > http://localhost:8090/servlet/UsefulAddresses for example, it loads
> with
> > > no
> > > > errors. However when I refresh the page I get this error:
> > > >
> > > > Error: 500: Location: /servlet/UsefulAddresses: Internal Servlet
> Error:
> > > > : java.lang.NullPointerException
> > > > at org.gjt.mm.mysql.Statement.executeQuery(Statement.java)
> > > > at org.gjt.mm.mysql.jdbc2.Statement.executeQuery(Statement.java:78)
> > > > at UsefulAddresses.doGet(UsefulAddresses.java:50)
> > > >
> > > > If i enter the servlet URL in the address bar again press return it
> > > returns
> > > > to the error free page! Every time I refresh this page or any other of
> my
> > > > servlets I get this error. Could anyone please tell me why this is. My
> > > > servlet code is the next email.
> > > >
> > > >
> > >
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