StackOverflow2013

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copied!<p>Oracle's JVM is only installed in one location. You've been misled!</p> <p>As you've noted, the Java commands in <code>/usr/bin</code> are symlinks to binaries in <code>/System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands</code>. The binaries within that directory are stub applications that determine which Java VM to use*, and then exec the corresponding real binary within that VM version. This is why all of the binaries within <code>/System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands</code> are almost identical in size, despite the fact that you'd expect them to be implementing quite different functionality.</p> <p>You can see this in action by using <code>dtrace</code>:</p> <pre><code>mrowe@angara:~$ sudo dtrace -n 'syscall::posix_spawn:entry { trace(copyinstr(arg1)); }' -c "/usr/bin/java -version" dtrace: description 'syscall::posix_spawn:entry ' matched 1 probe dtrace: pid 44727 has exited CPU ID FUNCTION:NAME 8 619 posix_spawn:entry /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/java </code></pre> <p>The given <code>dtrace</code> invocation prints out the path argument to <code>posix_spawn</code> when it is called by <code>java -version</code>. In my case the stub application has found Apple's Java 1.6 runtime in <code>/System/Library/Java/JavaVirtualMachines/1.6.0.jdk</code> and is invoking that version of the <code>java</code> command.</p> <p>The stub binaries also have another benefit: when they detect that no Java VM is installed they will prompt the user to install one.</p> <p>As for the <code>CurrentJDK</code> symlink, as best as I can tell this for sake of backwards-compatibility with the past when Apple was the only source of the JVM on OS X.</p> <hr> <p>* A combination of factors are considered when determining which Java VM should be used. <code>JAVA_HOME</code> is used if set (try <code>JAVA_HOME=/tmp java</code>). If <code>JAVA_HOME</code> is not set then the list of all virtual machines on the system is discovered. The <code>JAVA_VERSION</code> and <code>JAVA_ARCH</code> environment variables are used, if set, to filter the list of virtual machines to a particular version and supported architecture. The resulting list is then sorted by architecture (preferring 64-bit over 32-bit) and version (newer is better), and the best match is returned.</p>

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