检查当前系统中是否已安装JDK
[root@localhost ~]# java -version
openjdk version "1.8.0_242"
OpenJDK Runtime Environment (build 1.8.0_242-b08)
OpenJDK 64-Bit Server VM (build 25.242-b08, mixed mode)
检测系统JDK默认安装包
[root@localhost ~]# rpm -aq | grep java
java-1.8.0-openjdk-headless-1.8.0.242.b08-1.el7.x86_64
python-javapackages-3.4.1-11.el7.noarch
tzdata-java-2019c-1.el7.noarch
javapackages-tools-3.4.1-11.el7.noarch
java-1.8.0-openjdk-1.8.0.242.b08-1.el7.x86_64
卸载OpenJDK
卸载命令yum：
[root@localhost ~]# yum remove openjdk
检查
[root@localhost root]$ java -version
bash: java: 未找到命令...
安装JDK
mkdir /usr/local/jdk
上传jdk-8u221-linux-x64.tar.gz 至/usr/local/jdk
解压
tar -xvf jdk-8u221-linux-x64.tar.gz
mv jdk-8u221-linux-x64.tar.gz jdk1.8.0-221
配置环境变量
vim /etc/profile
export JAVA_HOME=/usr/local/jdk/jdk1.8.0_221
export JRE_HOME=#{JAVA_HOME}/jre
export CLASSPATH=.😒{JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=$PATH:${JAVA_HOME}/bin
source /etc/profile