The type BASE64Encoder is not accessible due to restrict

Access restriction: The type BASE64Encoder is not accessible due to restrict

在Eclipse中编写Java代码时，用到了BASE64Decoder，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 
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。

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Windows -> Preferences -> Java -> Compiler -> Errors/Warnings -> 
Deprecated and trstricted API -> Forbidden reference (access rules): -> change to warning