10.5以后的$JAVA_HOME没有被在.bash_profile中设置的话会被默认设置为 /usr/libexec/java_home。
如果一台mac里面安装了多个JDK， 可以通过/usr/libexec/java_home -V 来查看， 结果如下：
$ /usr/libexec/java_home -V
Matching Java Virtual Machines ():
1.7.0_13, x86_64:"Java SE 7"/Library/Java/JavaVirtualMachines/jdk1..0_13.jdk/Contents/Home
1.6.0_65-b14-, x86_64:"Java SE 6"/System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents/Home
1.6.0_65-b14-, i386:"Java SE 6"/System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents/Home
/Library/Java/JavaVirtualMachines/jdk1..0_13.jdk/Contents/Home
最后一行实际上反映的是系统默认使用的JAVA_HOME路径， 也就是执行/usr/libexec/java_home得到的路径。
如果想使用JDK1.6怎么办？
请在.bash_profile中添加
JAVA_HOME=$(/usr/libexec/java_home -v 1.6) export PATH=$PATH:$JAVA_HOME export JAVA_HOME
这样在bash下默认使用的就是JDK 1.6了
$ java -version java version "1.6.0_65" Java(TM) SE Runtime Environment (build 1.6.0_65-b14--11M4609) Java HotSpot(TM) -Bit Server VM (build 20.65-b04-, mixed mode)
另外要注意的一个地方是， 有些App是直接使用:
$ pwd
/System/Library/Frameworks/JavaVM.framework/Versions
$ ls -l
total
lrwxr-xr-x root wheel Feb : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6. -> CurrentJDK
drwxr-xr-x root wheel Feb : A
lrwxr-xr-x root wheel Feb : Current -> A
lrwxr-xr-x root wheel Feb : CurrentJDK -> /System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents
$
CurrentJDK来定位JDK路径的。一般如果JDK1.6是后安装的就会看到CurrentJDK为1.6。
要改的话：
$ ls -l
total
lrwxr-xr-x root wheel Feb : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6. -> CurrentJDK
drwxr-xr-x root wheel Feb : A
lrwxr-xr-x root wheel Feb : Current -> A
lrwxr-xr-x root wheel Feb : CurrentJDK -> /System/Library/Java/JavaVirtualMachines/1.6..jdk/Contents
$ sudo rm CurrentJDK
Password:
$ ln -s /Library/Java/
ln: ./: File exists
$ ls -l
total
lrwxr-xr-x root wheel Feb : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6. -> CurrentJDK
drwxr-xr-x root wheel Feb : A
lrwxr-xr-x root wheel Feb : Current -> A
$ ln -s /Library/Java/JavaVirtualMachines/jdk1..0_13.jdk/Contents CurrentJDK
$ ls -l
total
lrwxr-xr-x root wheel Feb : 1.4 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.4. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.5. -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6 -> CurrentJDK
lrwxr-xr-x root wheel Feb : 1.6. -> CurrentJDK
drwxr-xr-x root wheel Feb : A
lrwxr-xr-x root wheel Feb : Current -> A
lrwxr-xr-x root wheel Feb : CurrentJDK -> /Library/Java/JavaVirtualMachines/jdk1..0_13.jdk/Contents
$