How to change the default Java version on Ubuntu 18.04 LTS

  在Ubuntu环境下安装多个JDK版本也是很常见的，今天我们以Open JDK8与Open JDK11为例来介绍一下多JDK版本如何切换。

在目录/etc/jvm/中创建一个脚本文件，内容如下，并命名为switch-java-version.sh

#The set-default-java program is used to switch the Java version

process(){
  echo "process started."
  if [ $1 ]
    then
      sudo rm -rf /etc/profile.d/java.sh
      if [ "$1" -eq "0" ];
        then
          sudo update-java-alternatives --jre -s java-1.8.0-openjdk-amd64
          echo "export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-amd64" |sudo tee /etc/profile.d/java.sh
        else
          sudo update-java-alternatives --jre -s java-1.8.0-openjdk-amd64
          echo "export JAVA_HOME=/usr/lib/jvm/java-1.11.0-openjdk-amd64" |sudo tee /etc/profile.d/java.sh
      fi
      source /etc/profile.d/java.sh
  fi
  echo "process finished."
}

echo "Which version do you want to set the JDK for?"
echo "0 - java-1.8.0-openjdk-amd64."
echo "1 - java-1.11.0-openjdk-amd64."
read version

case $version in
0)
  echo "You choose the java-1.8.0-openjdk-amd64."
  process $version
  ;;
1)
  echo "You choose the java-1.11.0-openjdk-amd64."
  process $version
  ;;
*)
  echo "Incorrect choice."
esac

如何使用呢？执行如下命令即可。

lwk@qwfys:~$ source /etc/jvm/switch-java-version.sh