I have added commons-lang-2.6.jar & commons-lang3-3.1-sources.jar…
Here’s your problem: commons-lang-2.6.jar doesn’t contain the org.apache.commons.lang3 package, since that’s part of version 3, and commons-lang3-3.1-sources.jar contains the source code, not the byte code.
You need to include commons-lang3-3.1.jar instead.