Re: is it possible to package a Java application in one jar that includes everything?

Lew <>
Sun, 19 Feb 2012 22:41:26 -0800
Arne Vajh??j wrote:

Nasser M. Abbasi wrote:

Its been few years since I've used Java, since jdk 1.1 I think,
and I'd just like to ask a simple question:

Life has somewhat changed in Java universe since then.

Is it possible to package my Java application,
including all and any other Java code, that I might have
downloaded from the web and used, into one jar file,
such that one can just download this one jar file and
double click on it on their PC or Linux or Mac, and it
will run (ofcourse one needs to have the JRE installed
on their end).

Yes and no. The "jar" and "java -jar" commands /per se/ do not carry that
capability, but you can package things such that they will work.

Besides external packaging products, and Arne's excellent suggestion of Web
Start, the JAR format is intended as the vehicle to distribute Java
applications, but it does not pretend to package third-party works for you.
Nor should you be tempted to unpackage third-party work and package their
classes into your own JAR. That way lies madness.

If you study the JAR documentation you find the manifest file "MANIFEST.MF".
One of its elements is "Class-Path:", which specifies where third-party
libraries go *relative to the JAR* in its final resting place.

So the trick is to package third-party JARs with your JAR in parallel, or
conventionally, in a "lib/" subdirectory relative to your JAR's deployment.

The rest is packaging. I like ZIP. You put your JAR and all the library JARs
in a ZIP. It looks like this (from a project I just did as an exercise):

$ cd ~/projects/someproject/
$ ls configurator.* lib/

$ unzip -l
Unzip into desired directory, run 'java -jar configurator.jar &' from there.
   Length Date Time Name
--------- ---------- ----- ----
     23197 2012-02-11 19:25 configurator.jar
    481534 2012-02-11 15:40 lib/log4j-1.2.16.jar
--------- -------
    504731 2 files

Now that ZIP file is a complete distribution package for the 'configurator'

It is one step away from your request. You have to unpack the ZIP on the
target machine, say, into "/var/opt/configurator/".

$ ls /var/opt/configurator/ /var/opt/configurator/lib/
configurator.jar lib


Now a GUI can run "configurator.jar" with a double click if you associate JAR
files with the "java -jar" command.

Here's the manifest:
$ unzip -p configurator.jar META-INF/MANIFEST.MF
Manifest-Version: 1.0
Class-Path: lib/log4j-1.2.16.jar
Created-By: Lew Bloch
Main-Class: exercise.ui.ConfiguratorScreen

I've done something like this before, and I remember using
Makefiles and the jar command

jar cvf0 myjar.jar .../*.class

I assume only *.class files can go into a Jar. Can other
jar files go into a Jar file also?

Yes, but it won't help you. In fact, your assumption is wrong. You can put any
kind of file whatsoever into a JAR file. Why would you assume when you can
look it up?

For example, If I use 3rd party Jar file myself, do I
need to extract the content of that Jar file out first,
and then jar the resulting tree into my jar file?


Just wanted to check if things has changed, and if
there might be now better tools or ways to do this,
as I have not kept up with Java.

Things have changed, and there are other tools for other use cases, but really
nothing better than the JAR, which is magnificent for the purpose.

If someone has a good link I can read on this whole topic
of building one Jar for an application, and what to
watch for, that will help. I am using latest JDK.

Have you considered Googling for that?

Have you considered reading the Oracle Java site? You know, they really do
have some excellent documentation there. In fact, from the technologies page
there's a link right to a whole bunch of stuff about JARs, ion the column
labeled "Tools and Utilities"
Though sometimes (but not always) somewhat superficial, the tutorials are a
great introduction to all things Java

I am somewhat surprised you aren't using these resources, as they come from
the same site whence you get the downloads.

Java does not standard read jars in jars (you can get special
classloaders that can do it though).

You can obviously package all the class files you need
from various external jar files into you jar file.

But I will suggest that you keep your stuff in your jar
file and the external stuff in their jar files.


Quite aside from the compelling technical reasons to do things correctly, you
can have interesting licensing issues if you repackage other people's code
into your own.

That enables independent updates of your stuff and the
external stuff.

And if it is simplicity of distribution you need, then
take a look at Java Web Start.

JARs in ZIPs aren't all that complicated, and can boldly go where Web Start
sometimes can't. OTOH, Web Start handles dependencies for you when you can
rely on a suitable server for distribution.

But OP, all this is pretty accessible on the Java site, even if you aren't too
terribly familiar with it. In fact, there's a lot more there I haven't even
had time to suggest, so I suggest that you explore it fully. You'll get much
better answers more quickly from the material at your fingertips than trying
to piece it together piecemeal from Usenet posts, and you won't waste
everyone's time with stuff that is trivial for you to find out.

After that, IBM Developerworks has a ton of useful Java articles.

And remember, GIYF.

Honi soit qui mal y pense.

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