yum -y install java-1.8.0-openjdk java-1.8.0-openjdk-devel
dirname $(readlink $(readlink $(which java)))
【/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-3.b13.el7_5.x86_64/jre/bin】
vim /etc/profile
export JAVA_HOME=上面dirname命令获取到的路径，不要jre/bin最后这段
export PATH=$PATH:$JAVA_HOME/bin
export CLASSPATH=.:$JAVA_HOME/jre/lib:$JAVA_HOME/lib:$JAVA_HOME/lib/tools.jar
保存退出文件，然后执行一下使设置立即生效
source /etc/profile
[root@iZm5e46125tswtbtri94d1Z ~]# java -version
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)
