Re: Centralizing instantiation?

Lew <>
Tue, 25 May 2010 19:07:09 -0400
Rhino wrote:

Now, a few of the classes need database access - for example, I store
information about references there - and several of the classes have the
potential of generating log messages.

I'm trying to figure out when I should initialize the logging and
database connection.

You initialize logging via the framework, but you initialize a logger
separately for each class, or perhaps each instance.

You initialize the database setup when you load the driver, once, but not the

I'm leaning toward getting my database connection in the constructor of
the "mainline" and then passing that connection to each of the classes
that needs it as it is invoked in the mainline. I'm also leaning toward
getting my logger during the constructor of the mainline and, again,
passing it to each of the classes kicked off by the mainline.


Loggers are essentially self-initializing when the Logger class initializes.
Likewise the database driver. But not individual logger instances and not
individual DB connections.

This ensures that both the connection and logger are available to any
class that needs it. I'm also thinking that if creating the logger or
getting the database connection is a problem, I should probably find out

DB connections can drop at any time. Past checks are no guarantee against
future exceptions.

right at the start and probably abort the whole program if either one has
a problem. I'm inclined to think that if I'm unable to generate log
messages when I want to write them, that I shouldn't even get started.

The logging framework does that already.

The database connection is a little less categorical; if it is not
available, I could conceivably generate the resumes and simply display a
message to say that the references are not currently available so try
again later.

There is a difference between initializing the database driver and using a
particular connection. You don't really need to create one and only one
connection yourself - that's what a connection pool handles for you.

Don't reinvent the wheel.

I also don't know if connections can be managed very well if they're being
used all over the place at once. The recommended pattern is to obtain one,
use it and close it right away to release resources held by Statements and
ResultSets and the like. For example, how would you interleave separate
transactions? What if you needed different transaction isolation?

Arne Vajh??j wrote:

Both logging and database are rather well known problems with well known

For logging I would say no central initialization at all, but let
the logging stuff read the configuration file at first call and

For database you can either do something similar like have the
create connection code read the database configuration when needed
or if it is a heavy multithreaded app (does not sound like it) then
use a connection pool. A connection pool could also be initialized
at demand, but iy would be easier to justify initializing that at

Connection pools are essentially self-initializing - you use a pooling driver
and then just pretend each new connection really is new and not recycled.


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