Solved

In a servlet where should you create a JDBC connection?

Posted on 2002-07-30
3
169 Views
Last Modified: 2013-11-24
I've got a couple of textbooks about JDBC and servlets. They differ in where they create a connection.
One holds the connection as an instance variable; creates the connection in the init method; closes it in the doGet method and also closes it in the destroy method and in a finally clause.
The other author creates and closes the connection inside the try clause, no instance variable.
What are the advantages and disadvantages of each method?

Colin
0
Comment
Question by:cjmackenzie
  • 2
3 Comments
 
LVL 1

Accepted Solution

by:
twh270 earned 50 total points
ID: 7198376
A database connection is "expensive" to set up and tear down.  Most people use a connection pool to cache connections.  There are a lot of them out there, everything from free stuff to high-end expensive kits.  The servlet acquires a connection from the pool via something like "connectionPool.acquireConnection()" and releases it through e.g. "connectionPool.releaseConnection()".

To directly answer your question: Setting up the connection in init() means you create a single connection, only once, for the lifetime of each servlet instance.  This means you don't have the overhead of creating a database connection each time the servlet services a request, but it means only one request at a time can use the connection, so you'll need to synchronize access to it.  Creating a connection in try/catch means every request creates a new connection.  This is expensive.  However, it allows you to service N requests simultaneously.  (N is usually limited by the number of simultaneous connections your database allows.)

Both of these problems are mitigated through a connection pool (though not necessarily eliminated).

Keep in mind: textbook example code shows you how to write code that works.  It isn't intended to demonstrate good design.

-Thomas
0
 

Author Comment

by:cjmackenzie
ID: 7200606
Thanks Thomas, I was finding it hard to get my head round pooled connections and threads and your answer has helped clarify my options.
Within my application I have a static class that takes a connection and a query as parameters, then puts the results into a List of Javabeans for use in a JSP.
So I think I could very quickly improve the performance by creating the connection in the init method, then make the static method synchronized.
I am up against a deadline and I have a small number of potential users users, anyway (10 at the most). I don't think I've got time to look at pooled connections although that is obviously better still.


Colin
0
 
LVL 1

Expert Comment

by:twh270
ID: 7200978
Glad to help.

One thing I forgot to mention is that if the connection is unused for a long time it may timeout -- get closed by the database.  You can call Connection.isClosed() before using the connection.

-Thomas
0

Featured Post

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
groupNoAdj 7 95
Weekend adv creator 3 36
hibernate jars 4 26
JAVA API design with micro service cloud in mind 1 10
For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
I had a project requirement for a displaying a user workbench .This workbench would consist multiple data grids .In each grid the user will be able to see a large number of data. These data grids should allow the user to 1. Sort 2. Export the …
Viewers will learn about arithmetic and Boolean expressions in Java and the logical operators used to create Boolean expressions. We will cover the symbols used for arithmetic expressions and define each logical operator and how to use them in Boole…
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …

816 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

8 Experts available now in Live!

Get 1:1 Help Now