Why has it failed to load main-class manifest attribute from a JAR file?

Question

I have created a JAR file in this way jar cf jar-file input-files. Now, I'm trying to run it. Running it does not work (jre command is not found):

jre -cp app.jar MainClass

This does not work either:

java -jar main.jar

(Failed to load Main-Class manifest attribute from main.jar).

I also found out that

To run an application packaged as a JAR file (version 1.2 -- requires Main-Class manifest header)

What is the "Main-Class manifest header"? How do I create it and where do I put it?

Answer 1

I'm not sure I believe your symptoms:

• If the jre command isn't found, then running jre -cp app.jar should give the same error
• Just adding a JAR file to the classpath shouldn't give the error you're seeing

I'd expect you to see this error if you run:

java -jar app.jar

The Main-Class header needs to be in the manifest for the JAR file - this is metadata about things like other required libraries. See the Sun documentation for how to create an appropriate manifest. Basically you need to create a text file which includes a line like this:

Main-Class: MainClass

Then run

jar cfm app.jar manifest.txt *.class

Answer 2

1. set the classpath and compile

   javac -classpath "C:\Program Files\Java\jdk1.6.0_updateVersion\tools.jar" yourApp.java

2. create manifest.txt

   Main-Class: yourApp newline

3. create yourApp.jar

   jar cvf0m yourApp.jar manifest.txt yourApp.class

4. run yourApp.jar

   java -jar yourApp.jar

Answer 3

You can run with:

java -cp .;app.jar package.MainClass

It works for me if there is no manifest in the JAR file.

Answer 4

I got this error, and it was because I had the arguments in the wrong order:

CORRECT

java maui.main.Examples tagging -jar maui-1.0.jar 

WRONG

java -jar maui-1.0.jar maui.main.Examples tagging 

Answer 5

The easiest way to be sure that you have created the runnable JAR file correctly, with the appropriate manifest file, is to use Eclipse to build it for you. In your Eclipse project, you basically just select File/Export from the menu, and follow the prompts.

That way, you can be sure that your JAR file is correct and will know to look elsewhere if there is still an issue. The process is described in full in FAQ How do I create an executable JAR file for a stand-alone SWT program?.

Answer 6

I was getting the same error when i ran:
jar cvfm test.jar Test.class Manifest.txt

What resolved it was this:
jar cvfm test.jar Manifest.txt Test.class

My manifest has the entry point as given in oracle docs (make sure there is a new line character at the end of the file):
Main-Class: Test

Answer 7

Try

java -cp .:mail-1.4.1.jar JavaxMailHTML 

no need to have manifest file.