java on linux

[mikebw at colossus.bilow.com (Mike Bilow)]

Hmmm... so you work on the Island of Misfit Toys?

As a practical matter, you really need to have the latest stuff with Java.  
The changes are always major and you need to be on the cutting edge if you
want to work with the new J2EE components.  If you are dealing with
anything beyond basic Java, even common things such as JDBC or JNDI, then
you really need to be on Java 1.2 and cannot really get by with 1.1.

This rules out all of the open source VMs, unfortunately.  We have been
using the Sun JDK 1.2.2 on Linux, and it has worked.  This is with very
heavy use of J2EE extensions such as JNDI and even EJB.  In turn, this
forces the use of a fairly recent distribution of Linux, since you must be
on glibc 2.1.  In our case, we are using Debian Potato, which is not quite
released but is so far proving solid and reliable.

Debian also has a specific provision for mounting multiple concurrent
JVMs, using the "java-virtual-machine-dummy" package.  This works by
filtering all calls into "java" or "javac" through indirections in the
/etc/alternatives table, which is a standard part of Debian for things
other than Java also.

Privately, what I did was to install the JDK and other things into
versioned directories as local installations, and then to point
appropriate symbolic link at them:


mikebw at guardian:/usr/local/share$ ls -l
total 7288
lrwxrwxrwx    1 root     staff           8 Apr 26 01:14 jdk -> jdk1.2.2
drwxr-sr-x    8 root     staff        4096 Jan 12  2000 jdk1.2.2
lrwxrwxrwx    1 root     staff          10 Apr 26 01:13 jndi -> jndi_1.2.1
drwxr-sr-x    3 root     staff        4096 Apr 26 01:19 jndi_1.2.1
lrwxrwxrwx    1 root     staff          13 Apr 26 04:15 jonas -> jonas_jdk1.2/
drwxr-sr-x    9 root     staff        4096 Apr 26 06:03 jonas_jdk1.2


On a Debian Potato system, the important control files are /etc/java-vm
and /etc/java-c, and these require manual configuration:


mikebw at guardian:/etc$ cat java-vm
/usr/local/share/jdk/bin/java
/usr/local/share/jdk/lib:/usr/local/share/jndi/lib:/usr/local/share/java/lib
NONCOMPLIANT
#
# This file is referenced by the Debian Java Policy and is installed for
# compliance with the "java-virtual-machine-dummy" package.
# Line 1: path to the JVM installed, not necessarily under package control
# Line 2: path to use as default for CLASSPATH; Debian will append its own
#         /usr/share/java/repository (which is under package management and
#         should not be user-modified) when the JVM is invoked
# Line 3: magic keyword "COMPLIANT" will disable Debian adding its own
#         /usr/share/java/repository to CLASSPATH upon starting the JVM;
#         this makes the JVM strictly compliant with standard installation
# Line 4 and following are (at present) ignored
#
# -- Mike Bilow, 2000-04-25

mikebw at guardian:/etc$ cat java-c
/usr/local/share/jdk/bin/javac
/usr/local/share/jdk/lib:/usr/local/share/jndi/lib:/usr/local/share/java/lib
NONCOMPLIANT
#
# This file is referenced by the Debian Java Policy and is installed for
# compliance with the "java-compiler-dummy" package.
# Line 1: path to the javac installed, not necessarily under package control
# Line 2: path to use as default for CLASSPATH; Debian will append its own
#         /usr/share/java/repository (which is under package management and
#         should not be user-modified) when the JVM is invoked
# Line 3: magic keyword "COMPLIANT" will disable Debian adding its own
#         /usr/share/java/repository to CLASSPATH upon starting the JVM;
#         this makes the JVM strictly compliant with standard installation
# Line 4 and following are (at present) ignored
#
# -- Mike Bilow, 2000-04-25


In any case, by this point it ought to be fairly obvious how the system is
configured, and how it can be extended to support multiple concurent JVMs.

-- Mike


On 2000-06-29 at 19:01 -0400, Tom Guilderson wrote:

> Since our shop is moving towards java as the development
> language of choice; I need to come up with the right tools
> for the linux platform.
> 
> What jdk and jre?
> 
> kaffe?
> jikes?
> ibm jdk & jre 1.1.8 for linux
> sun's java 2 jdk and jre?
> blackdown?
> Visual age for linux? (I know Visual anything - eccchhh!)
> 
> I would prefer using open-source software. If it is as good or close to
> the best commercial binary software and the code will run in other 
> environments on other platforms (eg NT, solaris, aix), then that is my 
> preference.
> 
> Also if I want to have different jdk's and jre's living on the same 
> system for testing purposes, how difficult? Anyone have any experience 
> with this?
> 
> I would appreciate any and all feedback, comments, anyone has to offer
> on or off line.
> 
> TIA
> 
> --
> Tom Guilderson
> Applied Technology Team
> CVS Pharmacy
> mailto:TWGuilderson at cvs.com
> http://www.cvs.com/


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