CLASSPATH, Java Buld Path (eclipse), and WEB-INF\LIB : what to use, when, and why?

Question

I recently switched to J2EE from .NET, and am confused about where to put JAR files. I know that the CLASSPATH, WEB-INF, and Eclipse\'s Java Web Path are all places where J

Answer 1

Also, I know that WEB-INF\LIB is a place where you can put JAR files that your web app is going to use. However, I've put JARs in WEB-INF\LIB only to have them be ignored. In what situations should I put JARs into WEB-INF\LIB folder? How do I get Eclipse or the web server to notice them?

The real problem you have here is likely that you didn't got Eclipse for Java EE developers and/or that you just created a generic Java Project instead of a Dynamic Web Project and built up the necessary folder structure yourself.

If you create a Dynamic Web Project in Eclipse for Java EE developers, then Eclipse will automagically add any libraries in WEB-INF/lib to the build path. The build path is roughly said just the classpath which is been used in both compiletime and runtime. With other words: just drop the 3rd party JAR's in there, really nothing more needs to be done.

Note that Java is case sensitive, thus it should be really called WEB-INF/lib, not WEB-INF/LIB. But anyway, if you create a Dynamic Web Project, then Eclipse will just automagically generate the correct folder/file structure for you.

As said by others, ignore the %CLASSPATH% environment variable. It is only used by javac.exe/java.exe and even then only when you do not specify any of the -cp, -classpath or -jar arguments. In real world this environment variable is seldom used, it is just some convenience for starters (and unfortunately also the most confusing one, they should never have invented it).