RE: VMRuntime.insertSystemProperties(); java.ext.dirs

[David Holmes]

Steven Augart writes:
> I have been implementing the rest of the mandatory properties as
> listed in VMRuntime.insertSystemProperties().  I'm puzzled by the
> java.ext.dirs property ...
>
> I'm setting it to the empty string for now, in Jikes RVM's
> implementation.   But I wonder what it would mean if someone were to
> explicitly set it to another value.   Would it mean that the bootstrap
> class loader should start to look for javax.* classes wherever
> java.ext.dirs points?

java.ext.dirs defines the set of directories in which the extensions
classloader should look for standard extensions. Standard extensions have
different security privileges to normal user-defined code. If I had a jar
containg my favourite SPI implementation and added it's directory to
java.ext.dirs then I would expect the extensions loader to load that SPI
implementation.

The javax naming has nothing directly to do with this - other than certain
pre-packaged javax standard extensions will be found in the default
jre/lib/ext jar files that form the pre-installed standard extensions.

http://java.sun.com/j2se/1.4.2/docs/guide/extensions/index.html

When the VM starts up it should create the extensions classloader, with the
bootstrap loader as parent, then create the system/application class loader
with the extensions loader as parent.

Also note that once you start playing this game the role of the context
classloader for a thread becomes much more important :)

Hope this helps.

David Holmes