1、检测默认jre运行环境
（1） 查看linux7默认运行环境jre
# cd /etc/alternatives
# ll
如下图：
java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64/jre/bin/java
或者 使用以下命令输出：
# ls -lrt /etc/alternatives/java
lrwxrwxrwx. 1 root root 71 Apr 30 09:45 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64/jre/bin/java
# rpm -qa|grep openjdk -i
java-1.8.0-openjdk-headless-1.8.0.262.b10-1.el7.x86_64
java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
#
# find / -name java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm-exports/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm-private/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
#
（2） 检测开发环境jdk
[root@localhost lib]# javac
bash: javac: command not found...
Similar command is: 'java'
[root@localhost lib]#
（3） 联网安装开发环境jdk（无网建议卸载自带jdk和jre，安装统一版本的离线jdk）
3.1）检测yum源存在的jdk版本
[root@localhost lib]# yum search java|grep jdk
ldapjdk-javadoc.noarch : Javadoc for ldapjdk
......
......
java-1.8.0-openjdk.i686 : OpenJDK Runtime Environment 8
java-1.8.0-openjdk.x86_64 : OpenJDK 8 Runtime Environment
java-1.8.0-openjdk-accessibility.i686 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility.x86_64 : OpenJDK accessibility connector
java-1.8.0-openjdk-demo.i686 : OpenJDK Demos 8
java-1.8.0-openjdk-demo.x86_64 : OpenJDK 8 Demos
java-1.8.0-openjdk-devel.i686 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel.x86_64 : OpenJDK 8 Development Environment
java-1.8.0-openjdk-headless.i686 : OpenJDK Headless Runtime Environment 8
java-1.8.0-openjdk-headless.x86_64 : OpenJDK 8 Headless Runtime Environment
java-1.8.0-openjdk-javadoc.noarch : OpenJDK 8 API documentation
java-1.8.0-openjdk-javadoc-zip.noarch : OpenJDK 8 API documentation compressed
java-1.8.0-openjdk-src.i686 : OpenJDK Source Bundle 8
java-1.8.0-openjdk-src.x86_64 : OpenJDK 8 Source Bundle
......
......
ldapjdk.noarch : The Mozilla LDAP Java SDK
[root@localhost lib]#
附（参考）：
（1）单独安装jre命令：yum install java-1.8.0-openjdk
（2）单独安装jdk命令：yum install java-1.8.0-openjdk-devel.x86_64
3.2）yum方式安装jdk
执行以下命令可安装或升级默认jre：
# yum install java-1.8.0-openjdk
3.3）yum方式安装jdk（建议版本与jre版本保持一致）
# yum install java-1.8.0-openjdk-devel.x86_64
查看安装软件，如下图：
# rpm -qa|grep java-1.8.0-openjdk -i
jdk安装目录如下：
3、配置JAVA_HOME
# vim /etc/profile
（1）配置/etc/profile文件，在最后添加jdk配置信息
# jdk config
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.322.b06-1.el7_9.x86_64
export JRE_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.322.b06-1.el7_9.x86_64/jre
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$JAVA_HOME/bin:$JAVA_HOME/jre/bin:$PATH:$HOME/bin
重启加载环境变量配置，测试javac命令
[root@localhost jvm]# source /etc/profile
[root@localhost jvm]#
[root@localhost jvm]# javac
...
...
[root@localhost jvm]#
[root@localhost jvm]# javac -version
javac 1.8.0_322
[root@localhost jvm]#
