Hi all,
Is there a similar mailing list on Java language features?
Could somebody point me there?
Thanks.
--Ashwath
-----Original Message-----
From: Craig McClanahan <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Thursday, August 05, 1999 1:21 PM
Subject: Re: Thread safe JDBC connection
>Nitin Kulkarni wrote:
>
>> HI Chris
>>
>> Could you please elaborate a bit on this. I was/am under the impression
that
>> since init() is going to get called only once in a servlets life time
anything
>> we write in that is going to be thread safe. But your mails seems to say
that it
>> is/may not be so always.
>> Also what does ' the diff types of JDBC implementations' mean. Here
again I am
>> under the impression that JDBC since it is provided by sun it has to be
same
>> only we need diff drivers to connect to diff databases.
>> Please throw some light on this
>>
>
>The init() method indeed "thread safe" in the manner you are talking about.
In
>other words, the servlet engine guarantees that there will be only one
thread in the
>init() method, and that no calls to the service() method will occur until
init()
>returns.
>
>The place where you are still not necessarily safe is that, once the
service() calls
>start happening, the various calls will be sharing the single JDBC
connection that
>you created in the init() method. Some JDBC drivers will handle this
correctly, in
>the sense that you can have multiple statements and result sets open on the
same
>connection at the same time. However, you are almost certain to run into
>transaction problems if your database supports transactions (MySQL doesn't,
for
>example, but Oracle/Sybase/Postgres/etc. do). If you do a COMMIT or
ROLLBACK in the
>thread of one service() call, it will affect the statements currently
executing in
>*all* of them.
>
>The solution is to use a "connection pool" instead of a single connection.
As the
>name implies, you open a set of connections in the init() method, instead
of just
>one. Whenever a service() method call needs to access the database, it
does
>essentially this:
>* Allocates one of the connections from the pool
>* Does its JDBC calls on the connection that
> is, for the moment, dedicated to that thread.
>* Returns the connection to the pool.
>
>A good analogy to this is checking books out of a library -- the book is
available
>to everyone, but can be checked out and read by only one person at a time.
>
>There has been substantial discussion about connection pools, including
suggestions
>on some freely available ones, on this list. I suggest you peruse the
archives
>(http://archives.java.sun.com) and look for messages that have "connection
pool" or
>"connection broker" in their subjects.
>
>>
>> Thanks
>>
>> Nitin
>>
>
>Craig McClanahan
>
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