1 右击所选工程选择填出菜单里的Properties选项
2 在左侧菜单中选择Java Build Path
3 选择Libraies Tab，在此添加所需的jar包或者calss forlder
---原著
1)right click your project to select the Properties menu item.
2) select Java Build Path at the left Properties list
3) select Libraies Tab to set the class path. You can add Jars and
set class folder at there.