先移除JRE System Library，再添加库JRE System Library

osgi bundle

import sun.misc.BASE64Decoder;可是Eclipse提示：
Access restriction : The type BASE64Decoder is not accessible due to restriction on required library C:\Program
files\java\jre6\lib\rt.jar
Access restriction : The constructor BASE64Decoder() is not accessible due to restriction on required library C:\Program files\java\jre6\lib\rt.jar
搞不懂是为什么，最后在http://forums.dzone.com/eclipse/384-access-restriction-problems.html 找到答案，只需要在project build path中先移除JRE System Library，再添加库JRE System Library，重新编译后就一切正常了