Ubuntu 20.04 安装 oracle jdk 8

https://www.fosstechnix.com/install-oracle-java-8-on-ubuntu-20-04/

1. 下载 jdk-8u251-linux-x64.tar.gz

2. 解压

sudo mkdir  -p /opt/jdk
# 解压后放到/opt/jdk

3. Install Oracle Java 8 on Ubuntu 20.04 LTS with Alternatives

sudo update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_251/bin/java 100

4. 如果有多个版本可以这么切换

sudo update-alternatives --config java

5. 配置环境变量

# 编辑 /etc/environment ，填入以下内容
JAVA_HOME=/opt/jdk/jdk1.8.0_251
JRE_HOME=/opt/jdk/jdk1.8.0_251/jre
# 使生效
source /etc/environment