Access restriction: The type FtpClient is not accessible due to restriction on r

在做ftp，代码中引用
import sun.net.ftp.FtpClient;
报如下错误
Access restriction: The type FtpClient is not accessible due to restriction on required library D:/Program Files/Java/jre6/lib/rt.jar

sun.net包里的，在eclipse里默认是不让用的。解决办法是自定义access rules

工程上右键->工程属性->java builder path->Libraries标签，点击JRE System Library里面的Access rules，add sun/** 为accessible，如果该项存在，就edit。