jdk 官网：http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
[root@local-master software]# tar xf jdk-8u121-linux-x64.tar.gz
[root@local-master software]# ls /opt/software/
jdk1.8.0_121 jdk-8u121-linux-x64.tar.gz
[root@local-master software]# ln -s jdk1.8.0_121/ jdk
设置环境变量：
/etc/profile在文件末尾追加如下内容：
JAVA_HOME=/opt/software/jdk
JRE_HOME=$JAVA_HOME/jre
PATH=$PATH:$JAVA_HOME/bin
CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export JAVA_HOME
export JRE_HOME
export PATH
export CLASSPATH
source /etc/profile 更新环境变量
java -version 检查是否生效
