Is it ok to put configuration files in JARs?

We are having a debate at my office around what can and cannot go in a JAR file. It has been suggested that it is poor form to have anything that is not a .class file go into a JAR. We currently have some XML configur开发者_开发知识库ations for Ibatis/etc, some property files.. the usual. However, there is a push to extract all such files from JARs and put them onto the local file system of each deployment machine. Does this sound reasonable?

it is poor form to have anything that is not a .class file go into a JAR

That is nonsense. It is in fact very good form to put resources like icons and other data files that user used by the code into the JAR together with the code. This is what the getResource() and getResourceAsStream() methods of Class and ClassLoader are for, and it makes for much more robust applications than messing around with resource paths manually.

However, config files are possibly a different matter. If they're meant to be changed during or after deployment, then having them inside a JAR file is rather inconvenient, and having them in a separate directory is preferable.

If you make changes in a configuration file inside a JAR (even without altering any line of Java code), the whole JAR needs to be rebuilt and redeployed. Does this sound reasonable?

It's absolutely OK to put non-class files in a JAR file, especially resources that the application needs (images, localized strings, etc.) Knowing this, you must decide which scenario fits your situation:

• If the configuration is fixed and will only change when a new JAR file is deployed, put it in the JAR.
• If the configuration must be altered, either manually or by the application, store it on the filesystem.

If you choose the latter, note that it's good practice to include a default configuration in the JAR file to handle the case when the external configuration file is missing. The default can be loaded directly from the JAR or copied to the filesystem to become the new editable configuration.

It does not sound reasonable to me. I believe, that some application's configuration should be in jar file. Such things as ORM mappings, spring config, custom spring namespace XSD, other XSDs, etc.. should be in most cases in jar. It's important part of deployment artifact.

The fact, that it's not class file, does not mean, that it should be taken out of jar just because it's theoretically can be modified without building a new jar. Can you imagine a modification of *.hbm.xml in production? for me it sounds very scary.

I think some configuration, like spring xml, is meant in most cases to better organize your application and dependencies, but not to change them at runtime in production.

Do you want or expect them to be changed without a new release of the code? Then you need to extract them.

If the answer to the question in no than you shouldn't extract them, as it would allow support to tinker around with them without going through the release process. (Of course this is also possible if they are in the JAR but slightly less tempting.)

Update: But since you mentioned multiple deployment machines, there's a third option: extract them and place them in a commonly accessible area on a network drive. Manually editable config files which are replicated on several machines (but should be identical) are notorious for getting out of sync.

ORM tools (such as Hibernate or IBatis) are not really supposed to be modified once the application is deployed. So, no, I would say that it doesn't make sense for that kind of files.

Depending on your requirements, application-wide configuration files can be placed outside the Jar/War so that they can be modified without having to rebuild the jar. Do keep in mind that modifying application parameters in production is, imho, a bad practice. Changes should be tested first in some pre-production environment.