Eclipse running a java application and a jar file

Question

I am using Eclipse for running my applications.

=> All this time I have been running as a java application (using Run as Java application option) and it works.My program executes for 20 minutes and prints some data .

Now I tried to create a Runnable jar. I am able to get jar file and execute.But it exits after 1 minutes.There are no prints from SOP.I have kept one just immediately after main and that is also not getting printed. How to debug this?

I am getting this Error now:

JAR export finished with warnings. See details for additional information.
 Exported with compile warnings:input.java
 Jar export finished with problems. See details for additional information.
 Could not find main method from given launch configuration.

But there is a public static void main(String[] args) in the input.java file. I am not sure why is it complaining when I try to run from command prompt and it gives no main manifest attribute.I did not create any file with that name. What has gone wrong here ?

• Subhrajyoti Majumder: Not clear. Can you please Explain with some code snippet?
• The Learner: I have a program with 2 files. file1 and file2-has java main and calls file1. I was able to print data and all. but when I did jar file I am not able to print anything. infact there is no print line I have exactly after main ..so looks my main immedite line is not executed
• User404: How are you executing your .jar ?
• mcalex: what does your manifest look like?
• The Learner: I do not have manifest file. i am using Extract required binaries option. I had some warnings it says export with compile warning in details...not sure how to see the warnings

Answer 1

The problem you are mentioning is because, the compiler can not find the main class within the jar. To solve this we use a MANIFEST file.

A MANIFEST file is a special file that contains information about the files packaged in JAR

refer here for details on MANIFESTS

To solve your problem. we need to define a MANIFEST file and define the main Class inside it.

Create a MANIFEST.MF

file for your jar and specify the class that has the main method using format

Main-Class: Mypackage.yourPackhage.OurClass

UPDATE

when you are creating the JAR, follow Define Jar Manifest

to Include a Manifest file in your jar

UPDATE 2

Structure should be like

YourJAR
 META-INF\MANIFEST.MF
 CLASS1
 CLASS2

• The Learner: Thanks Mukul. what if I dont have ant package name? I have 2 files, 1 class is having main and another classs is used by main class. so how sould I have the contents. just main class is fine? and also the file structure where I should create?
• The Learner: I am seeing this Error: JAR export finished with warnings. See details for additional information. Exported with compile warnings: sample.java Jar export finished with problems. See details for additional information. Could not find main method from given launch configuration.
• Mukul Goel: if you dont have any package name, then just put the class name. you should create MAINFIEST.MF file inside a META-INF folder refer to update 2 for sample structure
• Mukul Goel: @TheLearner by the way, can you update the post with command for how did you create your jar and how are you running it?

Answer 2

A manifest is a one-line text file with a "Main-Class" directive. You need to create this file (call it something useful like manifest.txt) in notepad or wherever.

In the file you want the line: Main-Class: file2

make sure there's a hard return at the end of the line.

Then use jar like this: jar cvfm sample.jar manifest.txt *.class