All about java and jar files.

Here is a good article on java and jars.

http://fraaargh.wordpress.com/2008/07/13/how-to-java-jars-and-manifestmf/




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Some thoughts about things
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Use ANT to auto-generate the list of jar files in a MANIFEST.MF »
How-to java jars and MANIFEST.MF

Here’s a brief “how-to” for remembering what is possible with a jar file, how to use it, launch its main class and define where the other jars (the libraries used) are stored. I could not find anywhere on the net a good explanation of all this, so decided to write my own.
So imagine you have your own jar file named myApp.jar which main class (the one with the “main” method) is marot.francois.MyMainClass which needs to receive 2 arguments: arg1 and arg2 (passed in String[] args).

1- Without using any MANIFEST.MF fil

If you don’t have a MANIFEST.MF file in your jar, or if you want to set some specific places where Java should look for the libraries used by myApp.jar, then you should use the following command. Beware, the use of the star is only available since Java 6 (or is it Java 5 ?)

on Windows:
java -cp tmmerge.jar;myCustomLibPath1\*;myCustomLibPath2\*;myCustomLibPath3\* marot.francois.MyMainClass arg1 arg2
on Linux:
java -cp tmmerge.jar:myCustomLibPath1\*:myCustomLibPath2\*:myCustomLibPath3\* marot.francois.MyMainClass arg1 arg2

Same as previous one but with all the libraries’ jars listed instead of using *:
on Windows:
java -cp ./myApp.jar;myCustomLibPath1\sctm.jar;myCustomLibPath2\ant.jar;myCustomLibPath2\ant-launcher.jar;myCustomLibPath3\scdata.jar marot.francois.MyMainClass arg1 arg2

on Linux:
java -cp ./myApp.jar:myCustomLibPath1\sctm.jar:myCustomLibPath2\ant.jar:myCustomLibPath2\ant-launcher.jar:myCustomLibPath3\scdata.jar marot.francois.MyMainClass arg1 arg2

At first, I thought such a command line was overriding the classpath in MANIFEST.MF, if any. But that is not the case, the MANIFEST.MF is just bypassed.


2- Using a MANIFEST.MF file in the jar
Launch myApp using the jar files listed in myApp.jar’s own manifest
java -jar myApp.jar arg1 arg2

The content of the META-INF\MANIFEST.MF file must be:

Manifest-Version: 1.0
Ant-Version: Apache Ant 1.7.0
Created-By: 1.6.0_02-b06 (Sun Microsystems Inc.)
Main-Class: marot.francois.MyMainClass
Product-Name: myApp
Package-Title: marot.francois
Package-Version: 1.00.00
Package-Vendor: Elsys Design Avisto
Class-Path: myCustomLibPath2/ant-launcher.jar myCustomLibPath2/ant.jar myCustomLibPath3/scdata.jar myCustomLibPath1/sctm.jar

In a next post, I’ll show you how to use ANT to automatically generate the content listed here. And more specifically the list of libraries which would be error prone to write by hand.
By the way, I think it’s good to point to something important: in the “Class-Path”line of the manifest, you CAN’T use a star as you could do when specifying the classpath on the command line.
Also be aware that the space is the jars path delimiters as opposed to the “;” (windows) or “:” (Linux) on the command line. This last remark is very very error prone…

3- What I would like to be able to do (but it seems like Java doesn’t handle this case)

Warning: the exemple given hereafter does not work. I spent a lot of time trying to find some explanation of the reasons why, but was not able to find.
So the problem seems to be that you can’t override the default classpath specified in the jar’s manifest if you use the -cp switch at the same time. So the basic rule of thumb is:
“in java, do not use both switches -jar and -cp at the same time”: it does not work (at least up to Java 6).
I thought it would be cool to be able to run a jar but defining another place where it can find its dependancies. In case you want the users of your app to be able to use a shared folder containing the lib jars but don’t want him to have to know the main class’ name.
Here’s the command line I desperatly tryed to run:
REM java -cp myCustomLibPath1\*;myCustomLibPath2\*;myCustomLibPath3\* -jar myApp.jar arg1 arg2

Nevertheless, the same goal can be reached (successfuly) by using method 1. Only that the user needs to know the main class.

Tags: java jar manifest

This entry was posted on 2008-07-13 at 22:34 and is filed under Java, dev. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
6 Responses to “How-to java jars and MANIFEST.MF”

1. Use ANT to auto-generate the list of jar files in a MANIFEST.MF « Some thoughts about things Says:
2008-07-13 at 23:04

[...] Some thoughts about things Computing, IT, society… « How-to java jars and MANIFEST.MF [...]
2. Swathi Says:
2008-08-06 at 06:53

Thank you very much for the valuable inputs…
I am facing an issue.. I am using a junit library and built a test library testXXX.jar now this has a number of dependent jars say XXX.jar etc but how do i ask the testXXX.jar to use XXX.jar and execute the test library?
3. fraaargh Says:
2008-08-08 at 13:57

Swathi, I don’t really understand your problem there… Why can’t you use for testXXX.jar the same process used for your application’s main jar ?
4. Swathi Says:
2008-08-20 at 07:08

Actually i have one jar xxxlib.jar . Now from command line i ll be executing the jar yyylib.jar(inside that i have one property file prop.properties) which inturn use the xxxlib.jar. Now my problem is when i try to access the prop.properties while executing the yyylib.jar from cmd prompt i am not able to read the property file inside the yyylib.jar. I want to know how i can read this property file which is actually inside the jar?
5. fraaargh Says:
2008-08-20 at 21:45

If I understand, you try to access the *.properties file in xxxlib.jar from yyylib.jar… I never faced such a problem. Perhaps you could add a utility class in xxxlib.jar that would provide such an access through public methos ? Otherwise, try to find information on how to read files in jar files.
6. Swathi Says:
2008-09-10 at 13:18

Actually thats my doubt i am unable to read the property file inside the xxxlib.jar.

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