Opening newly created jar file - "Failed to load Main-Class manifest attribute"

I'm trying to make a jar file but it never seems to work.

I have three class files, one with the main method, in the folder "hexMaze." In command prompt, I go to this directory, then type in "jar cvf HexMaze.jar *":

Quote:

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C:\Documents and Settings\Aaron MacDonald\Desktop\hexMaze>jar cvf HexMaze.jar *
added manifest
adding: HexArray.class(in = 3460) (out= 2057)(deflated 40%)
adding: HexCell.class(in = 2780) (out= 1390)(deflated 50%)
adding: HexDisplay.class(in = 1538) (out= 940)(deflated 38%)

C:\Documents and Settings\Aaron MacDonald\Desktop\hexMaze>

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This makes the file HexMaze appear in my hexMaze folder. However, when I double-click it I get this error message:

Quote:

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Failed to load Main-Class manifest attribute from C:\Documents and Settings\Aaron MacDonald\Desktop\hexMaze\HexMaze.jar

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I also get this error message when I try to make my jar inside Eclipse. Can anyone tell me what's going on?

If it helps, I'm using jdk 1.5.03 on Windows XP. I believe my PATH variable is right, since I'm able to compile through the command promt (though when I try to run a file in the promt I get a bunch of NoClassDefFoundErrors...).

Could it be that you should have included a manifest file that names the class
containing the main method ?

O.K. The web page I looked at for instructions on creating jar files didn't mention me having to create a manifest file first. I'll search around some more.

Thanks.

UPDATE
I tried making a manifest file. I called it "mainClass.txt" and I put the line "Main-Class: HexDisplay.class" in it (I also tried not puting the extension on HexDisplay). Then in command prompt I typed "jar cvmf mainClass.txt
HexMaze.jar *.class":

Quote:

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C:\Documents and Settings\Aaron MacDonald\Desktop\hexMaze>jar cvmf mainClass.txt
HexMaze.jar *.class
added manifest
adding: HexArray.class(in = 3460) (out= 2057)(deflated 40%)
adding: HexCell.class(in = 2780) (out= 1390)(deflated 50%)
adding: HexDisplay.class(in = 1538) (out= 940)(deflated 38%)

C:\Documents and Settings\Aaron MacDonald\Desktop\hexMaze>

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This made HexMaze.jar appear in my folder, but I get the exact same error I got before when I try to open it!

Ok, i think the manifest file should have an .mf extension, I have made an executable
jar file from my 'cfe' package, the class with the main in is named App, and the
manifest file is named

manifest.mf

and its contents are:

Code:

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Manifest-Version: 1.0
Main-Class: cfe.App

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Nope, still doen't work.

I put this in my manifest file:

Quote:

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Manifest-Version: 1.0
Main-Class: hexMaze.HexDisplay

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Then I tried to make the jar like I did last time, but I got a "IOException: invalid header field". I tried taking out the line with "Manifest-Version: 1.0" and I got a jar file, but that error is still there.

I've exported runnable jars out of Eclipse. There's a place in the export dialog sequence where you tell it to generate a manifest and you pick the class containing main().

There you go :)

The Eclipse method worked perfectly. I didn't notice that field where you specify the main class (you have to click "next" twice). Thanks ray326.

Quote:

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(you have to click "next" twice)

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Finishing too soon is always a bad thing, or so I'm told. ;)

hi,

just update mail-class in manifest and give class path for external needed jar files.

put lib folder in your jar file folder(like dist folder and) and put your other jar files and related folders). This may help u.

Just follow these 4 steps: -

1. Create a file ( for eg. call it Manifest.text )
Specify your main class ( the class having public static void main(String [] args) method ) in the following format: -

Main-Class: <mainClass>

2. Hit enter in the same file ( the last line should be blank but it should be there, JVM ignores the last line )

3. Now, create your jar file, using the following command: -

jar cfm <jarName>.jar <Manifest.text> <contents>

4. Your are ready to double click the jar file!

For example: -

Your main file is HexDisplay.java,

create a file named Mainfest.text and write here

Main-Class: HexDisplay
with a new line after it.

Now, to make the jar file: -
Go the same directory where the contents are stored and execute

jar cfm HexMaze.jar Manifext.text .

the options cfm here tells -

c - create a jar file
f - put the output in the specified jar file
m - merge the contents of the default manifest file and the contents of the file specified.

It's done, run the jar file and your main class will get executed! :WAVE: