Linux Java JDK多版本管理自定义工具

为什么有其他工具还要自定义？

之前用过update-alternatives 这个命令管理 但是如果JDK版本更新了，文件夹一变，你就要重新改注册，你要各种拷贝目录…

我的工具基本原理

通过软连接的方式在环境变量中配置一个固定的路径，这样每次要切换JDK版本时，只要改变下这个软连接路径即可，其他不要动。
即使增加新版本，只要将JDK放到/usr/lib/jvm/目录下即可通过运行工具选择切换。

运行工具前的步骤

按照正常情况，JDK默认安装的位置是/usr/lib/jvm/，所以我也就按照这个默认的位置来，把JDK的文件夹（如：jdk1.8.0_231）不管是安装还是拷贝的方式都放到这个目录下。
然后，如果是第一次使用，还是要正常配置环境变量的，不过要按照如下规则配置，其中这个路径不能变（/usr/lib/jvm/java_home）

#set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/java_home ## Don't change this directory!!!
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH 

最后运行下命令source /etc/profile激活你设置的环境变量。

接着就可以运行工具了。

上代码

将下面代码保存为sh文件即可，然后直接运行。没有位置要求，如果经常用可以放到bin目录下使用。

#!/bin/bash
echo
echo "==================================================================="
echo "Please follow 3 steps as below before you select the JDK version!"
echo "Step 1:"
echo
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo "Please put jdk folder in '/usr/lib/jvm/', this program will scan 
JDK in this directory!"
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo
echo "Step 2:"
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo "Please append the text as below to file '/etc/profile'!"
echo "#----------------------------------------------------------"
echo "#set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/java_home ## Don't change this directory!!!
export JRE_HOME=\${JAVA_HOME}/jre  
export CLASSPATH=.:\${JAVA_HOME}/lib:\${JRE_HOME}/lib  
export PATH=\${JAVA_HOME}/bin:\$PATH  "
echo "#----------------------------------------------------------"
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo
echo "Step 3:"
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo "!!!Run command 'source /etc/profile' to activate the configuration!"
echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
echo
echo

echo -n  "Do you already has followed the three steps before? {[yes]|no}:"
read  answer
if [[ $answer =~ ^[N|n]o$ ]]; then 
    echo "exit."
    exit
fi
cd /usr/lib/jvm/
echo "There are JDK versions as below:"
jdks=`eval ls -d */|grep jdk`
#echo $jdks
jdkArr=($jdks);
#echo ${jdkArr[1]} --- ${!jdkArr[@]}

# print JDK directories and number
echo "============================="
printf "%s\t%s\n" "NO." "JDK" 
for i in "${!jdkArr[@]}";   
do   
    printf "%s\t%s\n" "$i" "${jdkArr[$i]}"  
done 
echo "============================="

# wait input and read number
echo -n  "please enter an number before the JDK:"
read  num
if [[ ! $num =~ ^-?[0-9]+$ ]]; then #validate is number or not
    echo "$num is not number. exit."
    exit
fi
if echo "${!jdkArr[@]}" | grep -w $num  &>/dev/null; then # validate number is in scope or not
    echo "The JDK you select is "${jdkArr[$num]}
else
    echo "The number you input is invalid. exit."
    exit
fi
# create soft link
sudo ln -s $PWD/${jdkArr[$num]} $PWD/java_home

echo "Done and enjoy!"
echo "============================="
java -version
echo 
echo 

exit

运行效果

谢谢大家！