Re: javaclasspath

[Rik]

On 12/15/2012 02:30 PM, address@hidden wrote:
> Message: 7
> Date: Sat, 15 Dec 2012 14:30:28 -0800 (PST)
> From: Philip Nienhuis <address@hidden>
> To: address@hidden
> Subject: Re: Opportunities for core work on Java
> Message-ID: <address@hidden>
> Content-Type: text/plain; charset=us-ascii
>
> Rik-4 wrote
>> > 12/14/12
>> > <snip>
>> > 1) javaclasspath.m needs to be able to set the classpath.
>> > 
>> > Currently the Octave version of javaclasspath only reads the current
>> > classpath variable.  For compatibility, and because it makes sense, we
>> > should be able to call javaclasspath (dpath) and directly set the value of
>> > the classpath.  The functionality we are trying to match is here
>> > (http://www.mathworks.com/help/matlab/ref/javaclasspath.html).  The change
>> > is pretty simple as well, call javaMethod with a "setProperty" method
>> > instead of a "getProperty" method.  Watch out that the path to octave.jar
>> > should always remain as the first element of the classpath.
> Is that really true? 
> IIRC octave.jar is implicitly in the path (i.e., in the static classpath). 
> >From what I understand of the ML docs, javaclasspath() is supposed to only
> be able to change the dynamic classpath (while yes, it can query both the
> dynamic and static classpaths).
> The static classpath is supposed to be just that: static. (It can be set in
> the "classpath.txt" file which is processed at startup of the JVM.)
I was misled by some comments in the m-file.  It is true, as you say, that
the static class path is set just once.  The reference behavior to match is
http://www.mathworks.com/help/matlab/matlab_external/bringing-java-classes-and-methods-into-matlab-workspace.html.

The static path is set by the file "javaclasspath.txt".  I made a change to
search for that file as well as "classpath.txt" here
(http://hg.savannah.gnu.org/hgweb/octave/rev/492893b98eef).  I made another
change here (http://hg.savannah.gnu.org/hgweb/octave/rev/ac9e34f83522) to
allow valid one-character paths like '/'.

Is there a good reason to hide octave.jar on the static classpath?  We are
doing that in javaclasspath.m but this seems unnecessary and misleading.

Do you have access to Matlab to try some experiments?  It seems that the
current working directory may be included by default in the dynamic path.
But, given that the paths in the classpath are absolute I think this must
mean the startup directory from which Matlab was launched.  Could you open
a brand new instance of Matlab and run 'javaclasspath' and report the output.

Also, the documentation seems to imply that every time the dynamic path is
modified ALL java objects are cleared.  Can you test that?

Sample Code:
clear all
x = javaObject ('java.lang.StringBuffer', 'Hello World')
whos
javaaddpath ('/tmp')
whos

>
> Anyway, a long time ago I peeked at how Martin Hepperle implemented the
> javarmpath() function; AFAIR it looked quite a bit more involved than just
> swapping getProperty for setProperty. But then I may be wrong.
>
>
This is true.  It looks like we can implement 'javaclasspath (dpath)' in a
straightforward, but braindead way, by looping over every path in the
current classpath and calling javarmpath on it it and then looping over
every path in dpath and calling javaaddpath on it.  Dumb, but performance
is not an issue here.

--Rik