Solution:
- Choose File, Project Properties. The Project Properties dialog opens.
- Click Libraries in the Categories pane, and then click the Add Library button. The Add Library dialog opens.
- Click the Create button. The Create New Library dialog opens.
- Enter e.g. HTTPClient in the Library Name field and click OK. The Customize Library dialog opens.
- Click Add JAR/Folder. The Browser JAR/Folder dialog opens.
- Find the folder where you saved unpacked HTTPClient and choose ALL the JAR files in the lib folder. Click Add JAR/Folder.
- In the Customize Library dialog, click OK.
- In the Add Library dialog, choose HTTPClient and click Add Library.
- In the Project Properties dialog, click OK.
Based on R. Cadenhead "Sams Teach Yourself Java in 24 Hours" [p. 303].