[fedora-java] java.home/java.library.path etc, what can I rely on ?

[Thomas Fitzsimmons]

Caolan McNamara wrote:
> So, for..
> 
> class findhome
> {
>         public static void main(String args[])
>         {
>                 System.out.println(System.getProperty("java.home"));
>                 System.out.println(System.getProperty("gnu.classpath.home.url"));
>                 System.out.println(System.getProperty("java.library.path"));
>         }
> }
> javac findhome.java 
> java findhome
> I have (on x86_64) ...
> 
> /usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
> file:///usr/lib64
> /usr/lib64/gcj-4.1.2
> 
> For something like OOo we have two sort of requirements, 
> 
> at run time we'd like to dlopen libjvm.so, currently the approach I took for gcj
> was to stick lib/ARCH/client/libjvm.so onto the value of java.home.

Unfortunately, Java vendors do not provide libjvm.so in a standard location 
relative to JAVA_HOME.  Your approach should work on RHEL- and Fedora-packaged 
GCJ 1.5.0, IcedTea and Sun JDKs.  The BEA location is lib/ARCH/jrockit/libjvm.so 
and the IBM location is bin/classic/libjvm.so or bin/j9vm/libjvm.so.

> I guess from the
> output here searching through java.library.path is also plausible ? 
> 
> The other requirement is at buildtime to link against libjawt.so and to find the 
> java headers.

The location of libjawt.so is JDK-dependent.  GCJ 1.5.0, IcedTea, Sun and BEA 
install it as lib/ARCH/libjawt.so.  IBM installs it as bin/libjawt.so.  The 
headers are always in ${java.home}/../include.

> 
> but for e.g. suse right now apparently the output of the above (for i386) is..
> 
> /usr
> file:///usr/lib/gcc/i586-suse-linux/4.2.1
> /usr/lib/gcj-4.2.1
> 
> So what I'm wondering is if there is a canonical reference to what the various 
> properties should refer to. i.e. are my assumptions just busted, or is e.g. the
> suse gcj misconfigured

I'd say SuSE gcj is misconfigured.  I had planned to add full support for 
JAVA_HOME to upstream GCJ; I got as far as adding a --with-java-home configure 
option which we set in Fedora.  The SuSE package doesn't set it, so java.home 
defaults to $prefix.

> and if there is more correct way to find libjvm.so. And
> while I'm at it is there a good solid cross platform and cross java-impl test
> to find the correct include and link path to build against the java headers and
> link to libjawt and friends.

See above.  Because of the lack of Java deployment standards, your tests will 
need to know specifics about the JDK you're building with.

Tom