sun.misc.BASE64Encoder找不到jar

myeclipse中編寫Java代碼時，用到了BASE64Decoder，importsun.misc.BASE64Decoder；可是Eclipse提示： 

Access restriction: The type BASE64Decoder is not accessible due torestriction on required library C:\Program 
files\java\jre6\lib\rt.jar 
Access restriction : The constructor BASE64Decoder() is notaccessible due to restriction on required library C:\Programfiles\java\jre6\lib\rt.jar 

解決方案1（推薦）： 
只需要在project build path中先移除JRE System Library，再添加庫JRE SystemLibrary，重新編譯後就一切正常了。 
解決方案2： 
Windows -> Preferences -> Java-> Compiler -> Errors/Warnings-> 
Deprecated and trstricted API -> Forbidden reference(access rules): -> change to warning