Access restriction: The type ‘BASE64Decoder’ is not API (restriction on required library ‘D:javajdk1.7.0_45jrelib t.jar’)
解决其实很简单，把JRE System Library移除重新添加即可。
方法：项目右键–>Properties–>Java Build Path，切换到libraries tab页，找到JRE System Library移除， 然后再点击Add Library–>JRE System Library添加即可。
如果import后仍然是报错！
图文来源：
https://blog.csdn.net/gnail_oug/article/details/53636428
https://blog.csdn.net/lvyanfen6/article/details/51121586