I’m pretty new to Servlets and JSP and to using databases.
At the moment I have a class in the ‘model’ part of my web app which has lots of methods that I’ve written to perform database queries and updates. At the moment, in each of those methods I am creating a database connection, doing the SQL stuff, then closing the connection.
This works fine while I’m just making small apps for myself but I’m starting to realise that if lots of people were using my app concurrently then it would start to become apparent that creating database connections and closing them for each method call is a time costly process. So I need to change the way I do things.
In Head First Servlet & JSP by Basham, Sierra & Bates, they describe how it’s possible to use a ServletContextListener implementation to create an object on the deployment of the web app that will be added as an attribute of the ServletContext. The authors don’t go into it, but imply that people often add a database connection as an attribute of the ServletContext. I thought I would like to implement this for myself, but after reading this stackoverflow article on database connection management I’m not so sure.
However as I’m just starting with servlets and JSP, let alone the rest of J2EE, a lot of that article is beyond me.
The points that stand out for me from that article are:
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Something could happen to break that database connection and if we are relying only on that connection then we would need to redeploy our app in order to restart a connection. is this correct?
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We should reply on the container to manage the database connections for us. Great, but how is this acheived? How can I communicate with the container? (Please bear in mind that I’ve just started with Servlets and JSP).
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In terms of Servlet design in general, I have one servlet class per request type and that normally only has one type of call to a database ie a specific update or query. Instead of having a class with all the methods for querying the database, is it a better design for me to have the methods within their respective servlets or would that contravene the Model-View-Controller pattern?
I can’t imagine that I’ll be having too many problems with too many users slowing down the user experience just yet 🙂 but I’d like to start doing things right if possible.
Many thanks in advance for your comments
Joe
The following page on Tomcat’s website describes how to connect Tomcat and mySQL in detail. You do not want to roll your own, there are too many DataSource pools already available that have been debugged and tried in production environments.
The main thing about using a pool is that a connection is not terminated when you call close, instead it is just returned to the pool. Therefore it is important to make sure that you close your resources in a try/finally block. Look here for a sample.