CentOS 7 yum installation and configuration of JDK detailed

first step

• Check if your machine has jdk installed

java -version
yum list installed | grep [java][jdk]

• If so, please uninstall it first (as shown above)
• Uninstall

yum -y remove java-1.8.0-openjdk*  //表时卸载所有openjdk相关文件输入
yum -y remove tzdata-java.noarch   //卸载tzdata-java

Second step

• Install jdk
• View jdk version

yum search java | grep -i --color jdk

• Choose the version to install, or the second command is simple and rude

yum install -y java-1.8.0-openjdk java-1.8.0-openjdk-devel
#或者如下命令，安装jdk1.8.0的所有文件
yum install -y java-1.8.0-openjdk*

• Check if the installation is successful

java -version

third step

• Configure environment variables
• JDK default installation path /usr/lib/jvm

ls /usr/lib/jvm

• Add the following commands to the /etc/profile file

vim /etc/profile

# set java environment  
JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64
PATH=$PATH:$JAVA_HOME/bin  
CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar  
export JAVA_HOME  CLASSPATH  PATH 

• Save and close the profile file, execute the following command to take effect

source  /etc/profile

• Use the following command to view the JDK variables

 echo $JAVA_HOME
 echo $PATH
 echo $CLASSPATH