[Anomalous]

Hi,

I am developing a Java application, which I am able to pack into a JAR file by using the "jar -cvf target.jar source" command. However, I am unable to make this JAR executable.

I have followed the standard procedure of using the command "jar -cvmf myManifest.mf...", where myManifest.mf is a text file containing the line "Main-Class: ClassName". However, even when I use this custom manifest file, when I try to execute the JAR with the java -jar command, I get an error saying that the Main-Class attribute couldn't be read from the manifest. I also tried expanding the JAR and looking at the manifest, and the Main-Class information was indeed missing from it. Any suggestions? Thanks.

[Arkham_c]

Your manifest should go in META-INF/MANIFEST.MF and should look something like this:

Code:
Manifest-Version: 1.0
Main-Class: com.mydomain.myClass
Created-By: Anomalous

Then when you create the jar, do the following:

Code:

jar -cmf mymanifestfile myjarfile com/mydomain/myClass

The "m" flag tells it you want to use your own manifest file rather than theirs.

[Anomalous]

Thanks for your suggestions.

When I tried this, I think I have successfully used a custom manifest file now, but when I try to execute the JAR, I get a "class not found" error.

I'm not exactly sure what you mean by com and mydomain.

[Arkham_c]

Originally posted by Anomalous:
Thanks for your suggestions.

When I tried this, I think I have successfully used a custom manifest file now, but when I try to execute the JAR, I get a "class not found" error.

I'm not exactly sure what you mean by com and mydomain.

Most java files are part of a package. At the top of the source there is a line that describes what package it is in, that looks like this:

Code:
package mypackage;

Typically, in order to ensure that your package name is unique across all java classes, the package is prefixed with your domain name in reverse order. For example, my domain is theresistance.net, and I have an Email package with SMTP and POP classes. At the top of all these source files is:

Code:
package net.theresistance.Email;

The code is then stored on the file system in net/theresistance/Email/somefile.java. If I wanted my default class in the manifest to be POPClient.class, then the way it is specified in the maifest is:

Code:
Main-Class: net.theresistance.Email.POPClient

In a simple example, you might not have a package. In this case, just remove all the domain stuff.

I tarred/gzipped up my sample code that I used to write the original reply. It's on my web site here for you to look at:

http://david.theresistance.net/files/jar_classtest.tgz

It's very simple and should remove any ambiguity caused by my poor explanation. Hope this helps.

[Anomalous]

Thanks for the sample code. Your explanation is not poor - I am just a little confused. I will keep looking to try to figure out what I am doing differently from your example.

[int69h]

Originally posted by Anomalous:

However, even when I use this custom manifest file, when I try to execute the JAR with the java -jar command, I get an error saying that the Main-Class attribute couldn't be read from the manifest.

I didn't test the OS X jdk, but the Blackdown linux jar command is pretty picky about the last line of your manifest containing a newline. If you don't have one it won't add that attribute. I must have said WTF 10 times in the last five minutes.

Glad to see you got your problem solved.

[Anomalous]

Okay, by moving the files around I was able to get an executable JAR file working. However, I tried to embed my program's image and sound files into the JAR, and the program couldn't locate them at runtime. How can I refer to files within the JAR?

[Arkham_c]

Originally posted by Anomalous:
Okay, by moving the files around I was able to get an executable JAR file working. However, I tried to embed my program's image and sound files into the JAR, and the program couldn't locate them at runtime. How can I refer to files within the JAR?

I suspect your answer is here:

http://developer.java.sun.com/developer/qow/archive/76/

[Anomalous]

Originally posted by Arkham_c:
I suspect your answer is here:

http://developer.java.sun.com/developer/qow/archive/76/

Thanks for the link.

[Arkham_c]

Originally posted by Anomalous:
Thanks for the link.

Google is great.

Just prepend "site:java.sun.com" as an argument to java-related queries and you can find anything about java in a flash.