缘由：
更新sdk，遇到了更新下载失败问题：
Fetching https://dl-ssl.google.com/android/repository/addons_list-2.xml
Fetched Add-ons List successfully
Fetching URL: https://dl-ssl.google.com/android/repository/repository-8.xml
Done loading packages.
Fetching https://dl-ssl.google.com/android/repository/addons_list-2.xml
Failed to fetch URL https://dl-ssl.google.com/android/repository/addons_list-2.xml, reason: Connection to https://dl-ssl.google.com refused
Fetched Add-ons List successfully
Fetching URL: https://dl-ssl.google.com/android/repository/repository-8.xml
Failed to fetch URL https://dl-ssl.google.com/android/repository/repository-8.xml, reason: HttpHostConnect Connection to https://dl-ssl.google.com refused
Done loading packages.
遂百度，网上有很多文章有说到这个，但是因为大陆政策问题，像更改hosts文件等方法，我这都没解决问题，最后还是强大的开源力量啊，开源万岁，配置步骤如下：
1.启动 Android SDK Manager ，打开主界面，依次选择「Tools」、「Options...」，弹出『Android SDK Manager - Settings』窗口；
2.在『Android SDK Manager - Settings』窗口中，在「HTTP Proxy Server」和「HTTP Proxy Port」输入框内填入mirrors.neusoft.edu.cn和80，并且选中「Force https://... sources to be fetched using http://...」复选框。设置完成后单击「Close」按钮关闭『Android SDK Manager - Settings』窗口返回到主界面；
3.依次选择「Packages」、「Reload」。