将下载的jdk文件解压到 /usr/lib/jvm目录下
sudo nano /etc/profile
修改 /etc目录下的 profile文件，在末尾添加：
set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_171
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:$PATH
设置系统默认jdk 版本
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0_171/bin/java 300
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0_171/bin/javac 300
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.8.0_171/bin/jar 300
sudo update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/jdk1.8.0_171/bin/javah 300
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.8.0_171/bin/javap 300
运行如下命令,切换jdk版本:
sudo update-alternatives --config java
查看jdk版本：
java -version
