1. yum -y install java-1.8.0-openjdk.x86_64
    2. which java
    3. ls -l /usr/bin/java
    4. ls -l /etc/alternatives/java
    5. # java安装目录
    6. /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.292.b10-1.el7_9.x86_64/jre
    7. vim /etc/profile
    8. export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.292.b10-1.el7_9.x86_64/jre
    9. export PATH=$PATH:$JAVA_HOME/bin
    10. export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
    11. source /etc/profile