使用下面指令添加了一个源：
sudo add-apt-repository ppa:webupd8team/java
然后update的时候提示：
W: Failed to fetch http://ppa.launchpad.net/webupd8team/java/ubuntu/dists/trusty/main/binary-amd64/Packages: 403 Forbidden [IP: 112.124.140.210 80]
W: Failed to fetch http://ppa.launchpad.net/webupd8team/java/ubuntu/dists/trusty/main/binary-i386/Packages: 403 Forbidden [IP: 112.124.140.210 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
E: Couldn't rebuild package cache
根据网友的提示，看了一下apt的设置，发现以下配置：
Acquire::http::Proxy "http://mirrors.aliyun.com/";
注释掉，就Ok了，阿里云对镜像的此类修改有点不合理。