Ubuntu下切换多个JDK环境

cf2000

　　安装Ubuntu时，默认安装了OpenJDK_1.7
　　$ java -version
　　java version "1.7.0_79"
　　OpenJDK Runtime Environment (IcedTea 2.5.6) (7u79-2.5.6-0ubuntu1.12.04.1)
　　OpenJDK 64-Bit Server VM (build 24.79-b02, mixed mode)
　　

　　现在需要安装JDK_1.6
　　安装在/opt/java/jdk1.6.0_45
　　/opt/java/jdk1.6.0_45# ls
　　bin        db       jre  LICENSE  README.html  THIRDPARTYLICENSEREADME.txt
　　COPYRIGHT  include  lib  man      src.zip
　　

　　加上环境变量
　　用户环境变量：~/.bashrc中增加行
　　export JAVA_HOME=/opt/java/jdk1.6.0_45
　　export JRE_HOME=$JAVA_HOME/jre
　　export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JRE_HOME/lib/tools.jar
　　export PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin
　　export USE_CCACHE=1
　　

　　系统环境变量：/etc/profile中增加行
　　export JAVA_HOME=/opt/java/jdk1.6.0_45
　　export JRE_HOME=$JAVA_HOME/jre
　　export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JRE_HOME/lib/tools.jar
　　export PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin
　　export USE_CCACHE=1
　　

　　通过update-alternatives切换软件版本
　　增加JDK_1.6的命令连接符，使用--install选项
　　$ sudo update-alternatives --install /usr/bin/java java /opt/java/jdk1.6.0_45/bin/java 1062  
　　如需移除，--remove选项
　　$ sudo update-alternatives --remove /usr/bin/java java /opt/java/jdk1.6.0_45/bin/java 1062
　　创建默认命令链接 --config
　　$ sudo update-alternatives --config java
　　There are 2 choices for the alternative java (providing /usr/bin/java).
　　

　　Selection    Path                   Priority  Status
　　------------------------------------------------------------------------------------
　　* 0    /opt/java/jdk1.6.0_45/bin/java            1062      auto mode
　　1    /opt/java/jdk1.6.0_45/bin/java            1062      manual mode
　　2    /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1051      manual mode
　　

　　Press enter to keep the current choice

, or type selection number:0
　　

　　同理Python也可以这样切换
　　

　　2017-6-16新增
　　更为详细的英文引用mark如下：
Use Oracle Java JDK, by following the steps below:

• 　　Visit http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase6-419409.html
  
• 　　Accept the license agreement
  
• 　　Download jdk-6uXX-linux-x64.bin (where XX is the latest minor version)
  
• 　　If you don't have an Oracle account and don't want to create one, you can have a look at http://bugmenot.com/view/oracle.com
  

Here is how to configure Oracle Java JDK to be the default on Ubuntu:
cd /usr/lib/jvm && sudo /bin/sh ~/Downloads/jdk-6u38-linux-x64.bin -noregisterNote: You might get /bin/sh: jdk-6u43-linux-x64.bin: Permission denied error. This happens because root does not permissions to read the ~/Downloads folder.
Option 1: Temporarily change the permissions of ~/Downloads folder for root to have read permission.
chmod 755 ~/Downloads/Don’t forget to change it back once you are done!
Option 2: Copy the downloaded file to /usr/lib/jvm and do
sudo /bin/sh jdk-6u38-linux-x64.bin -noregisterIn either case, then set it as default.
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.6.0_38/bin/javac 50000
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.6.0_38/bin/java 50000
sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/jdk1.6.0_38/bin/javaws 50000
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.6.0_38/bin/javap 50000
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.6.0_38/bin/jar 50000
sudo update-alternatives --install /usr/bin/jarsigner jarsigner /usr/lib/jvm/jdk1.6.0_38/bin/jarsigner 50000
sudo update-alternatives --config javac
sudo update-alternatives --config java
sudo update-alternatives --config javaws
sudo update-alternatives --config javap
sudo update-alternatives --config jar
sudo update-alternatives --config jarsignerAlso make sure /usr/bin/java is first in your $PATH. i.e.
which javashould return /usr/bin/java.