/etc/profile jdk配置环境变量

export JAVA_HOME=/opt/jdk1.8.0_241
export JRE_HOME=JAVA_HOME/jre
export PATH=PATH:JAVA_HOME/bin:JRE_HOME/bin
export CLASSPATH=.:JAVA_HOME/lib/dt.jar:JAVA_HOME/lib/tools.jar:$JRE_HOME/lib
export JAVA_HOME JRE_HOME PATH CLASSPATH