测试
/etc/profile配置
export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$PATH:$JAVA_HOME/bin
使用update-alternatives切换JAVA
hadoop@note50064:~$ which java
/usr/bin/java
hadoop@note50064:~$ sudo update-alternatives --config java
There are 2 choices for the alternative .
Selection Path Priority Status
------------------------------------------------------------
0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1072 auto mode
* 1 /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java 1071 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1072 manual mode
Press enter to keep the current choice[*], or type selection number:
hadoop@note50064:~$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 Nov 21 03:26 /usr/bin/java -> /etc/alternatives/java
hadoop@note50064:~$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 46 Nov 1 01:44 /etc/alternatives/java -> /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
hadoop@note50064:~$ java -version
java version "1.7.0_121"
OpenJDK Runtime Environment (IcedTea 2.6.8) (7u121-2.6.8-1ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.121-b00, mixed mode)
hadoop@note50064:~$ $JAVA_HOME/bin/java -version
java version "1.7.0_121"
OpenJDK Runtime Environment (IcedTea 2.6.8) (7u121-2.6.8-1ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.121-b00, mixed mode)
hadoop@note50064:~$
hadoop@note50064:~$ sudo update-alternatives --config java
There are 2 choices for the alternative .
Selection Path Priority Status
------------------------------------------------------------
0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1072 auto mode
* 1 /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java 1071 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1072 manual mode
Press enter to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/lib/jvm/ in manual mode
hadoop@note50064:~$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 39 Nov 1 01:45 /etc/alternatives/java -> /usr/lib/jvm/java-7-oracle/jre/bin/java
hadoop@note50064:~$ java -version
java version "1.7.0_80"
hadoop@note50064:~$ $JAVA_HOME/bin/java -version
java version "1.7.0_121"
OpenJDK Runtime Environment (IcedTea 2.6.8) (7u121-2.6.8-1ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.121-b00, mixed mode)
分析
Alternatives是使用符号连接管理已装软件位置的工具。例外我们通常在命令行使用的java命令使用的是/usr/bin/java；而/usr/bin/java指向/etc/alternatives/java，/etc/alternatives/java指向的是真正某个JRE/JDK包下的java命令。 尽管可以使用Alternatives工具切换JAVA，但是由于我的JAVA_HOME始终指向OpenJDK，所以$JAVA_HOME/bin/java不会随Alternatives的指定而切换。这样使用JAVA_HOME环境变量的Hadoop等工具一直用OpenJDK。
方案
更改/etc/profile配置：
export
export JDK_HOME=$(readlink -f /usr/bin/
export CLASSPATH=.:$JDK_HOME/lib/dt.jar:$JDK_HOME/lib/tools.jar
export PATH=$PATH:$JAVA_HOME/bin
这样通过update-alternatives命令更改java和javac后，重启命令行后JAVA_HOME和JDK_HOME也随之更新。 这个方案自己不甚满意，有时间再继续研究吧。
参考
What is the difference between JAVA_HOME and update-alternatives?
Setting up your Linux environment to support multiple versions of Java
Using the Debian alternatives system
update-alternatives - Linux man page