SAP delivers basis libraries which you have to transport once through your system landscape to fill the build spaces before starting your development. If you want to make modifications to Java components of the Employee Self-Service (ESS) or Customer Relationship Management (CRM) application, then you also have to load the related sources into the development configuration.
Note that the archives and sources have to be transported again after every support package or patch import.
With SAP NetWeaver 7.3 you can use the Synchronize Service instead of the Upload System. The Synchronize Service reads all necessary information from the runtime system and loads the relevant sources and archives from the inbox. This means it is no longer necessary to import sources and archives manually.
More information about the Synchronize Service, see Using the Synchronize Service.