最近在配置WSL的环境，全部重置了一遍，装Java的时候，打算装一个Java8和一个Java17。本篇文章就是来处理不同Java安装以及Java版本的切换
Java8 安装
下载Java8 JDK包
以Java8为例子，我们要安装JDK版本，链接如下
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| https://www.oracle.com/java/technologies/downloads/
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下载jdk-8u401-linux-x64.tar.gz。
建立Java8目录
我们建立Java的安装目录
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| sudo mkdir -p /usr/lib/java8
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解压Java包至Java8目录
我是WSL，所以可以直接从主机复制到目录里
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| cd /usr/lib/java8
sudo tar xzvf jdk-8u401-linux-x64.tar_2.gz
rm jdk-8u401-linux-x64.tar_2.gz
cd jdk1.8.0_401
ls
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添加环境变量
最末尾处添加
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| JAVA_HOME=/usr/lib/java8/jdk1.8.0_401
PATH=$PATH:$HOME/bin:$JAVA_HOME/bin
export JAVA_HOME
export PATH
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注册Java8
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| sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/java8/jdk1.8.0_401/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/java8/jdk1.8.0_401/bin/javac" 1
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/java8/jdk1.8.0_401/bin/javaws" 1
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/java8/jdk1.8.0_401/bin/javaws" 1
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检测
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| ┌──(root㉿Desktop-Trtyr)-[~]
└─# java -version
java version "1.8.0_401"
Java(TM) SE Runtime Environment (build 1.8.0_401-b10)
Java HotSpot(TM) 64-Bit Server VM (build 25.401-b10, mixed mode)
┌──(root㉿Desktop-Trtyr)-[~]
└─# javac -version
javac 1.8.0_401
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安装成功
Java17 安装
同样的方法，安装Java17，我是放在目录/usr/lib/java17/jdk-17.0.10下了，不过这次，不需要添加环境变量了
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| 下载java17 JDK包 -> 建立目录/usr/lib/java17 -> 压缩至目录 -> 注册
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注册如下
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| sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/java17/jdk-17.0.10/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/java17/jdk-17.0.10/bin/javac" 1
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切换版本
先看一下当前啥版本
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| ┌──(root㉿Desktop-Trtyr)-[~]
└─# java -version
java version "1.8.0_401"
Java(TM) SE Runtime Environment (build 1.8.0_401-b10)
Java HotSpot(TM) 64-Bit Server VM (build 25.401-b10, mixed mode)
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查看所有的Java版本
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| ┌──(root㉿Desktop-Trtyr)-[~]
└─# update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/lib/java8/jdk1.8.0_401/bin/java 1 auto mode
1 /usr/lib/java17/jdk-17.0.10/bin/java 1 manual mode
* 2 /usr/lib/java8/jdk1.8.0_401/bin/java 1 manual mode
Press <enter> to keep the current choice[*], or type selection number:
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我们现在是用的2，输入1就可以切换到Java17。
如果切换后出现
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| -bash: /usr/bin/java: Permission denied
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使用命令
然后是切换javac
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| ┌──(root㉿Desktop-Trtyr)-[~]
└─# update-alternatives --config javac
There are 2 choices for the alternative javac (providing /usr/bin/javac).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/java8/jdk1.8.0_401/bin/javac 1 auto mode
1 /usr/lib/java17/jdk-17.0.10/bin/javac 1 manual mode
2 /usr/lib/java8/jdk1.8.0_401/bin/javac 1 manual mode
Press <enter> to keep the current choice[*], or type selection number:
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一样。
