java -version查询一下是否安装

查询已经安装的jdk的包

rpm -qa | grep -i jdk
rpm -qa | grep java

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[root@yc-nsg-e16 ~]# rpm -qa | grep -i jdk
java-1.8.0-openjdk-headless-1.8.0.312.b07-1.el7_9.x86_64
copy-jdk-configs-3.3-10.el7_5.noarch
java-1.8.0-openjdk-1.8.0.312.b07-1.el7_9.x86_64

使用rpm -e –nodeps 命令卸载这些默认安装的jdk版本

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[root@yc-nsg-e16 ~]# rpm -e --nodeps java-1.8.0-openjdk-headless-1.8.0.312.b07-1.el7_9.x86_64
[root@yc-nsg-e16 ~]# rpm -e --nodeps copy-jdk-configs-3.3-10.el7_5.noarch
[root@yc-nsg-e16 ~]#  rpm -e --nodeps java-1.8.0-openjdk-1.8.0.312.b07-1.el7_9.x86_64

[root@yc-nsg-e16 ~]# java
-bash: java: command not found

安装JDK

安装

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[root@VM_0_13_centos]~# yum install java-1.8.0-openjdk  java-1.8.0-openjdk-devel

配置

用[root@VM_0_13_centos]~# rpm -ql java-1.8.0-openjdk命令查看jdk安装路径，只需要 /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64目录

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[root@yc-nsg-e16 ~]# rpm -ql java-1.8.0-openjdk
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64/jre/bin/policytool
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64/jre/lib/amd64/libawt_xawt.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64/jre/lib/amd64/libjawt.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64/jre/lib/amd64/libjsoundalsa.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64/jre/lib/amd64/libsplashscreen.so
/usr/share/applications/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64-policytool.desktop
/usr/share/icons/hicolor/16x16/apps/java-1.8.0-openjdk.png
/usr/share/icons/hicolor/24x24/apps/java-1.8.0-openjdk.png
/usr/share/icons/hicolor/32x32/apps/java-1.8.0-openjdk.png
/usr/share/icons/hicolor/48x48/apps/java-1.8.0-openjdk.png

编辑配置文件：vi /etc/profile，在文件末尾加上：

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export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.345.b01-1.el7_9.x86_64
export CLASSPATH=.:$JAVA_HOME/jre/lib/rt.jar:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$PATH:$JAVA_HOME/bin

执行source /etc/profile命令使配置生效