1. custom library
Window-> Preferences-> Java-> Build Path-> User Libraries-> New-> for the new custom user library name is not checked (as shown), then OK, just click the name of the library custom - > Add External JARs (jar package added) -> Apply and Close
2. Introduction of a custom library
Right project name -> Properties-> Java Build Path-> Libraries-> Add Library-> User Library-> Next and just check the custom library -> Apply and Close
You can see just a custom library in the project