sun.misc.BASE64Encoder找不到jar包的解决方法

在MyEclipse中编写Java代码时，用到了BASE64Decoder，需要导入import sun.misc.BASE64Decoder；但无法导入该包，且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 

解决方案1（推荐）： 
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。 
解决方案2： 
Windows -> Preferences -> Java -> Compiler -> Errors/Warnings -> 
Deprecated and trstricted API -> Forbidden reference (access rules): -> change to warning