Java Web Application Configuration Patterns
Solution 1:
I'm surprised that no one cited the Jakarta Commons Configuration API (http://commons.apache.org/configuration/) to answer this question. It allows you to have a hierarchy of files (or other configuration sources like XML, JNDI, JDBC, etc.). That's what Jeremy Seghi was talking about and it gives you a good way to have both defaults and local overrides as well.
The best part is that it is a tested working solution so you don't have to go craft something yourself.
Solution 2:
I tend to work more with .NET lately, so my Java is fairly rusty. I'm pretty sure this would work in any language with a little tweaking.
We use an extension of the .NET configuration system that allows us to use environment and/or application specific settings in conjunction with a more global configuration. The configuration system uses a Global setting to each machine identifies it as dev, beta, or production (the default). A set of files loaded in order, and the setting from the last file overrides any setting that was defined in a previously loaded file. Files are loaded in the following order:
- Global settings
- Application specific settings
- Application specific environment overrides
All the files are in source control, and since the environment is defined on the machine the application is running on; since it won't access the "beta" configuration unless the machine configuration identifies it as "beta", we can promote all of the configuration files without fear of inadvertently pointing our production application to a dev database.