尝试在类似情况下做些对我有帮助的事情:

Try to do what helped me in similiar case:

• 转到Oracle JDK 8下载页面，并下载与oracle-java8-installer尝试下载的完全相同的jdk版本.您的情况是jdk-8u20-linux-x64.tar.gz.因此，您应该从以下网址下载: http://www.oracle.com/technetwork/java/javase/downloads/java-archive-javase8-2177648.html
• 将jdk-8u20-linux-x64.tar.gz复制到以下文件夹:/var/cache/oracle-jdk8-installer/

• 尝试安装oracle-java8-installer:

• go to Oracle JDK 8 download page and download exactly same version of jdk that oracle-java8-installer tried to download. In your case it's jdk-8u20-linux-x64.tar.gz. So you should download from: http://www.oracle.com/technetwork/java/javase/downloads/java-archive-javase8-2177648.html
• copy jdk-8u20-linux-x64.tar.gz to folder: /var/cache/oracle-jdk8-installer/

• try install oracle-java8-installer:

sudo apt-get install oracle-java8-installer

这应该可以解决问题.