NAME

NAME
Java::SJ - Highly configurable Java program startup system

SYNOPSIS
sj myprogram.sj

DESCRIPTION
This module allows you to very easily run Java services that rely on
complex configuration at the VM and library level. It also provides an
easy way of specifying a sensible 'default' configuration that can be
overridden by specific applications should they need to.

The system is configured on a machine and application level. The system
looks for configuration files in a set of well-known locations,
currently these are:

* /etc/sj.conf
* .sj.conf in users HOME directory
* .sj.conf in current working directory

Every application is defined in terms of a similar configuration file.
The configuration system has been designed so that it is easy to write a
simple and minimal configuration file for a program.

Provided the system has a fairly complete configuration associated with
it then an application configuration file need only have the class name
to be executed.

FEATURES
Some of the Goodness(tm) that you get with SJ is as follows:

Easy co-existence of multiple Virtual Machines
Any number of VMs can be supported and used concurrently on the same
machine. Developers don't need to know where the JDK/JRE resides,
just a symbolic name for it.

Easy co-existence of multiple versions of JAR files
Any number of different versions of the same JAR file may co-exist.
SJ sorts out which ones to use and only places those JAR files that
are required in an application's CLASSPATH

Control over BOOTCLASSPATH variables
All three flavours of the bootclasspath can be configured on a
system-wide and application specific basis.

Process control
PID files can be automatically generated and placed wherever you
wish.

Cache of executable scripts
Application configuration files are cached as executable scripts
that can be directly invoked.

This will probably make more sense as a set of examples, so here goes.

EXAMPLES
Simple Configuration
<?xml version="1.0"?>
<sj>

<vm name="ibm"
home="/usr/local/IBMJava-1.3.1"
default="true"/>
</sj>

The above minimal system configuration simply tells the system where to
find a virtual machine called 'ibm' and that it should be used as the
default VM unless an application specifically requests another one.

<?xml version="1.0"?>
<sj>

<class>myclass</class>
</sj>

The above minimal application configuration simply provides a class file
name to run. If both of the above simple configuration files were used
then the class 'myclass' would have to be in the system's CLASSPATH
environment variable already.

Useful Configuration
The above simple configuration is only really useful to test that the
system is working. Running a simple class on the command line isn't
normally very difficult and so sj doesn't actually add very much to the
above case.

If we had a system where we wished to test that the same code was
compatible with multiple virtual machines and multiple library versions
then the following configuration files would enable us to run these
programs with different parameters easily.

<?xml version="1.0"?>
<sj>

<var name="dir.base" value="/usr/local"/>
<var name="dir.pid" value="${dir.base}/var/run"/>
<var name="dir.log" value="${dir.base}/var/log/sj"/>
<var name="dir.tmp" value="/tmp"/>
<var name="dir.lib" value="${dir.base}/lib/sj"/>
<var name="dir.script" value="${dir.base}/var/sj/script"/>


<pid/>


<classpath>
<jar name="xalan"/>
<jar name="xerces"/>
<jar name="xml-apis"/>
<jar name="commons-cli" version="1.0.3"/>
</classpath>

<vm name="ibm118"
vendor="IBM"
version="1.1.8"
home="/usr/local/IBMJava-1.1.8"/>

<vm name="ibm141"
vendor="IBM"
version="1.4.1"
home="/usr/local/IBMJava-1.4.1"/>

<vm name="blackdown118"
vendor="Blackdown"
version="1.1.8"
home="/usr/local/blackdown-1_1_8"/>

<vm name="sun131"
vendor="Sun Microsystems"
version="1.3.1"
home="/usr/local/sunjdk_131"
default="true"/>
</sj>

The above system configuration contains a lot more information than our
initial simple example.

Variables
There are explicitly declared variables that SJ will use when
figuring out where things should be read from/written to.

Variables may be defined in terms of other variables, even if they
have not been declared yet. The syntax for referring to variables
thorughout is the same as Ant, ${variable_name}.

PID file
It states that by default a PID file should be written when running
an application. This is most useful for multithreaded server
applications where you want to be able to kill or HUP the server
without figuring out what the lead process PID is.

Classpath
The classpath definition instructs SJ to look for the latest
available versions of xalan, xerces and xml-apis and version 1.0.3
of the commons-cli libraries and add these to the classpath when
running any program.

SJ will look for the libraries in the path defined by ${dir.lib}.

SJ is currently very simplistic about library versioning. If it
needs to look for a specific version of a library then it simply
looks for the library name and library version number joined by a
single hyphen. So in the case of the commons-cli library SJ would
look for commons-cli-1.0.3.jar in the ${dir.lib} directory.

You may be wondering how SJ figures out which is the 'latest'
version of a JAR file if no version is specified. Quite simply it
chooses the one whose filename begins with the required name and is
lexicographically last in an ordered list of those filenames that
match. It's not great but with any half-sensible version numbering
scheme it will work.

Virtual Machines
There are four virtual machines defined here. In addition to the
home directory for each there is now information regarding the
vendor and version. Currently this is for informational purposes
only but future versions of SJ should be able to choose a VM based
on the version or vendor.

<?xml version="1.0"?>
<sj>

<class>myclass</class>
<vm ref="blackdown118"/>
</sj>

<?xml version="1.0"?>
<sj>

<class>myclass</class>
<vm ref="ibm118"/>
</sj>

<?xml version="1.0"?>
<sj>

<class>myclass</class>
<vm ref="sun131"/>
</sj>

The above application configurations are exactly the same as the simple
version with the addition of a vm reference tag to determine which VM
they should be executed under.

High Granularity
In addition to being able to specify which VMs and libraries to use you
have complete control over the environment that the VM is run under, the
properties that are passed the the VM and even default command line
options on a per system, VM and application basis.

<?xml version="1.0"?>
<sj>

<var name="dir.base" value="/usr/local"/>
<var name="dir.pid" value="${dir.base}/var/run"/>
<var name="dir.log" value="${dir.base}/var/log/sj"/>
<var name="dir.tmp" value="/tmp"/>
<var name="dir.lib" value="${dir.base}/lib/sj"/>
<var name="dir.script" value="${dir.base}/var/sj/script"/>


<property name="ORBSingletonClass" value="jacorb.ORBSingleton"/>


<environment name="TZ" value="CET"/>
<environment name="PAGER" value="less"/>


<param name="--debuglevel" value="3"/>
<param name="--colour" value="blue" sep="="/>
<param name="-g" value="3" sep=":"/>


<pid/>


<classpath>
<jar name="xalan"/>
<jar name="xerces"/>
<jar name="xml-apis"/>
<jar name="commons-cli" version="1.0.3"/>
</classpath>

<vm name="ibm118"
vendor="IBM"
version="1.1.8"
home="/usr/local/IBMJava-1.1.8">

<environment name="USE_JIT" value="true"/>
</vm>

<vm name="ibm141"
vendor="IBM"
version="1.4.1"
home="/usr/local/IBMJava-1.4.1"/>

<vm name="blackdown118"
vendor="Blackdown"
version="1.1.8"
home="/usr/local/blackdown-1_1_8">

<param name="-Xmx" value="81920k" sep=""/>
</vm>

<vm name="sun131"
vendor="Sun Microsystems"
version="1.3.1"
home="/usr/local/sunjdk_131"
default="true"/>
</sj>

The above system configuration is identical to our useful configuration
except we have now added directives that SJ will use to alter the
environment and command line parameters passed to the application and
VMs.

Using VM specific parameters you can make sure that the correct
threading models are used or that memory limuts are enforced unless
someone needs to tweak the settings.

In an application configuration file it is possible to override
previously declared parameters such as the -Xmx directive above for the
blackdown VM.

For example:

<?xml version="1.0"?>
<sj>

<class>myclass</class>
<vm ref="blackdown118">
<param name="-Xmx" value="80m" sep=""/>
</vm>
</sj>

The Java::SJ::Config documentation describes every configuration
directive in detail, also have a look in the sample directory for ideas.

TODO
Test, test, test.

BUGS
None known so far. Please report any and all to Nigel Rantor
<[email protected]>

SUPPORT / WARRANTY
This module is free software. IT COMES WITHOUT WARRANTY OF ANY KIND.

LICENSE
The Java::SJ module is Copyright (c) 2003 Nigel Rantor. England. All
rights reserved.

You may distribute under the terms of either the GNU General Public
License or the Artistic License, as specified in the Perl README file.

AUTHORS
Nigel Rantor <[email protected]>

SEE ALSO
Java::SJ::Config.