1.添加webupd8team Java PPA(Personal Package Archives) repository到系统里;
$ vim /etc/apt/sources.list.d/java-8-debian.list
deb http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main
deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main
2.在安装之前导入GPG key到系统验证包的合法性;
$ apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EEA14886
出现以下的错误提示：
Error:
Executing: /tmp/apt-key-gpghome.iKAAqs0hjL/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys EEA14886
gpg: failed to start the dirmngr '/usr/bin/dirmngr': No such file or directory
gpg: connecting dirmngr at '/tmp/apt-key-gpghome.iKAAqs0hjL/S.dirmngr' failed: No such file or directory
gpg: keyserver receive failed: No dirmngr
Tip:No dirmngr
提示没有dirmngr，安装dirmngr：
$ apt-get install software-properties-common dirmngr
$ apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EEA14886
3.apt-get update(更新索引文件);
$ apt-get update
4.安装java8;
$ apt-get install oracle-java8-installer
5.查看java版本，以及java, javac命令是否可用；
$ java -version
$ java
$ javac
6.将oracle-java8设置为默认的java环境；
$ apt-get install oracle-java8-set-default