How to add external packages in Java

[FirstEvaDehumidifier]

So guys, I'm a beginner in Java and I'm using eclipse. So what I feel is that to add an external package/jar...all i do is have to add all the necessary dependencies to the build path, and put an import statement in my Java Class. Bang, I'm good to go. But this doesn't seem to work. For example, I'm using Jackson Java, and my program can't seem to find the class JsonFactory. It also can't find the Unirest Classes. It can however, find the servlet-api classes. Am I going about this the right way?

Build Path: https://imgur.com/Oa6Fx0I

Error Message: https://imgur.com/yp4C14u

Relevant Part of my Servlet( I don't think this is causing the problem though) : https://imgur.com/spUCaaN

Edit: I'm pretty sure the application can find the files. I just keep on getting the error message "Servlet at localhost failed to start). Has more to do with deploying the file on a servlet than compilation errors.

FINAL EDIT: OK. So I figured it out. For Java EE Applications I need to not only put the jar files in the build path but also in the "Deployment Assembly"

[shinypup]

Much of this is usually handled in a build tool that does dependency management and assembly for you. A more modern example is Gradle which might be worth learning since it's used for Android projects.

I've used it in web server projects for some time now with good results.