Centos7自带了OpenJDK1.8，我们不想要。想用JDK8，怎么办：
-
Download JDK1.8 rpm:
wget http://download.oracle.com/otn-pub/java/jdk/8u101-b13/jdk-8u101-linux-x64.rpm -
Install JDK1.8:
sudo rpm -ivh jdk-8u101-linux-x64.rpm -
Switch from Open JDK to Oracle JDK:
sudo alternatives --config java* (Select the item for jdk1.8) * - Check it:
which java
java -version
which javac
javac -version
