个人博客地址：Mac OS JAVA_HOME设置 | 一张假钞的真实世界
在MacOS上使用DMG文件安装了Jdk8 之后，在默认路径下找不到JDK的HOME路径：
$ which java
/usr/bin/java
$ ls -l /usr/bin/java
lrwxr-xr-x 1 root wheel 74 12 6 2015 /usr/bin/java -> /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/java
$ ls -l /System/Library/Frameworks/JavaVM.framework/Versions
total 8
drwxr-xr-x 10 root wheel 340 5 9 20:45 A
lrwxr-xr-x 1 root wheel 1 12 6 2015 Current -> A
$ ls -l /System/Library/Frameworks/JavaVM.framework/Versions/A/
total 80
drwxr-xr-x 47 root wheel 1598 10 18 2015 Commands
drwxr-xr-x 4 root wheel 136 10 18 2015 Frameworks
drwxr-xr-x 14 root wheel 476 8 2 2015 Headers
drwxr-xr-x 3 root wheel 102 8 23 2015 JavaPluginCocoa.bundle
-rwxr-xr-x 1 root wheel 109488 10 18 2015 JavaVM
drwxr-xr-x 3 root wheel 102 8 2 2015 Modules
drwxr-xr-x 45 root wheel 1530 10 18 2015 Resources
drwxr-xr-x 3 root wheel 102 8 23 2015 _CodeSignature
在MacOS下可以使用/usr/libexec/java_home命令来定位JAVA_HOME：
$ /usr/libexec/java_home
/Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home
设置JAVA_HOME：
export JAVA_HOME=`/usr/libexec/java_home`
检查JAVA_HOME：
$ echo $JAVA_HOME
/Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home
如果安装了多个版本的JDK，可以使用-V命令选项列出所有版本的JAVA_HOME：
$ /usr/libexec/java_home -V
Matching Java Virtual Machines (1):
1.8.0_91, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home
/Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home