Eclipse warning: XXXXXXXXXXX.jar will not be exported or published. Runtime ClassNotFoundExceptions may result

In order to get it to work right, I have to "drop and drag" the files that I want in my classpath/dependencies into my the WEB-INF/lib folder. It works this way.

For some reason, when I try to do it the right way

Build path → Configure build path → External jars

it just doesn't take them.

The trick is that I have to put the files int my Web App Libraries folder and the only way to do that (that I can see) is to "click and drop" into my WEB-INF/lib folder. In this way, it automatically shows up in my Web App Libraries.

When adding new jar files, I got two messages on Eclipse's Problems Tab: one error and one warning. I only solved this problem when combining all previous solutions with an extra step. Here's how I solved it:

1. "Drag and drop" the files that I want in my classpath/dependencies into my WEB-INF/lib/ folder;
2. Right-click on your project in the Package Explorer tab, and build path --> configure build path --> external jars, adding the desired files;
3. Restarted Eclipse;
4. Select Project --> Clean…. My system is configured to build automatically, so after this step, the error message was gone, but the warning XXXXXXXXXXX.jar will not be exported or published. Runtime ClassNotFoundExceptions may result remained;
5. Right-click on warning message --> Quick Fix;
6. Select the option Mark the associated raw classpath entry as a publish/export dependency. (in the following figure)

Right-click on your project in the 'Project Explorer' tab and go to 'Build path' → 'Configure build path' → 'External jars`, and add all the JARs that you want.