practicing techie

Mac OS X is a nice platform for Java development because it successfully combines a very good desktop user experience with the system’s unix heritage and tooling. There are some problems, however:

• only a limited set of JDK versions are available for current OS X releases
• the JVM implementations are not standalone and require Apple proprietary frameworks to be present

In this respect, Linux is probably the best Java development platform because JDKs are available from many different vendors and multiple versions of the most popular JDKs run on Linux. The JVM implementations, usually don’t have esoteric dependencies and only require basic OS libraries in addition to the ones bundled with the JVM.

On the other hand, only Apple and Oracle provided JDKs run on Mac OS X and older Java versions aren’t available. Also, neither Apple’s Java 6 nor Oracle’s Java 7 JVM seems to run on Lion or Mountain Lion without the com.apple.pkg.JavaEssentials package, for example.

Recently, I managed to corrupt my Java installation beyond repair and I wanted to try and avoid this in the future by trying to isolate my Java 7 and 8 installations as much as possible. This turned out to be fairly simple if you defy the temptation to install by just clicking on the downloaded JDK package. The JDKs are distributed by Oracle as disk images that contain a Mac OS X installer package file. Instead of running the installer you can easily extract the contents of the package using command line tools. First mount the disk image by clicking on the disk image and then run the following commands in a terminal session:

xar -xf '/Volumes/JDK 8/JDK 8.pkg'
cat jdk180.pkg/Payload | gunzip | cpio -i

After that, the Contents directory will include the entire JDK installation and you can move it to the location of your choosing. Then just specify JAVA_HOME environment variable and add the JVM and required tools to shell search path.

After downloading and installing Java SE 7 update 6 I tried running “java -version” to verify that the JDK was installed properly. To my surprise, the command reported the previous version instead of update 6. I then tried troubleshooting the problem using:

pkgutil --verbose --files com.oracle.jdk7u6
installer -dumplog -verbose -pkg '/Volumes/JDK 7 Update 06/JDK 7 Update 06.pkg' -target /

but with no effect. Then, browsing through the previous Java 7 installation directory parent directories I noticed that with update 6 the installation path was actually

/Library/Java/JavaVirtualMachines/jdk1.7.0_06.jdk

instead of

/Library/Java/JavaVirtualMachines/1.7.0.jdk

as with the previous Java 7 update releases, so I was using the old absolute path in my “java -version” command.

Now, on Linux one of my first troubleshooting methods would’ve been to use the strace command, but for some reason this doesn’t come instinctively for me on Mac OS X. On the Mac the equivalent command is called dtruss and it would’ve revealed the new installation path immediately, as strace would’ve:

dtruss 'installer -dumplog -verbose -pkg /Volumes/JDK\ 7\ Update\ 06/JDK\ 7\ Update\ 06.pkg -target /'
...
kevent(0x3, 0x153C67788, 0x1) = 1 0
audit_session_self(0x7FB1EB9640E0, 0x7FB1EBBEB150, 0x78) = 6659 0
kevent(0x3, 0x153C67788, 0x1) = 1 0
lstat64("/Library/Java/JavaVirtualMachines/jdk1.7.0_06.jdk", 0x153C65860, 0x1) = -1 Err#2
stat64("/Library/Java/JavaVirtualMachines/jdk1.7.0_06.jdk", 0x153C668B8, 0x0) = -1 Err#2
getattrlist("/", 0x153C665A0, 0x153C66190) = 0 0
getattrlist("/Library/Internet Plug-Ins/JavaAppletPlugin.plugin", 0x153C665A0, 0x153C66190) = 0 0
...

So, when troubleshooting OS level problems, system call tracing is always your friend, irrespective of the operating system. This is a good case in point.