27.安装jdk，配置环境变量

vi /etc/profile

export JAVA_HOME=/usr/local/jdk1.8.0_221
export CLASSPATH=.:$JAVA_HOME/jre/lib/rt.jar:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$PATH:$JAVA_HOME/bin

source /etc/profile

java -version