Java BASE64Decoder in Eclipse issue

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

解決方法 :
在project build path中先移除JRE System Library，
再添加 JRE System Library，重新编译后就一切正常了