Q:
I am porting a Java product to Mac OS X. What are the equivalents
for directories and paths common to JDK installations on
other platforms?
A:
Since J2SE is a preinstalled component on every copy of Mac
OS X, the location and structure of the Java VM is controlled
and consistent. User input should not be required to retrieve
information on Java-related paths and directories.
Java Home. Many Java applications require the identification
of a "Java Home" directory during installation.
The equivalent on Mac OS X should always be /Library/Java/Home. This is actually a symbolic link to the current installed
J2SE version, and allows access to the bin subdirectory where
command line tools such as java, javac, etc. exist as expected.
The advantage of using this link, as opposed to its target,
is that it will be maintained and updated when a new version
of Java is downloaded via Software Update or installed with
a newer version of Mac OS X. For this reason, it is important
that developers do not install files below the Java Home,
as the actual directory referenced by the link will be lost
with subsequent updates when the link is updated by newer versions of Java.
Extension Libraries. Java software on other platforms often
makes use of the lib/ext directory within a JDK installation
to store support class or jar files. While
the Mac OS X java home also contains a lib/ext directory,
it is not recommended that developers directly make use of
it for the same reason mentioned above. Similar to the java
home situation, Apple has provided standardized paths for
extension libraries to be placed. The /Library/Java/Extensions
directory can be used for additional jar files or JNI libraries that need
to be placed on the system classpath. For more controlled
access, a ~Library/Java/Extensions directory off of a given
user's home directory can be used for user-level installation
of support libraries. Items placed in either of these directories
do not need to be named in an application's classpath and
will be available to all applications run under the applicable
scope (user-level or system-level, depending on which directory
is used).
Please note that these extension directories are for jar files and JNI libraries only. Directories of classfiles, even if properly laid out to match your packages, are not picked up. If you want to use these provided extension directories, package your support Java classes into jar files. JNI libraries can go in as-is.
User Preferences. Many applications choose their own installed directory structure for storing settings and user preferences. Others try to make use of whatever preference system exists on the host platform. In the latter case, on Mac OS X, user preferences for an application are typically stored in the ~/Library/Preferences directory, if those preferences are to be on a per-user basis. This directory could be reached from Java code by appending the String "Library/Preferences" to the user.home System property. An application that should have global preferences across all users could instead reside in /Library/Preferences from root.
[Oct 21, 2003]
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