Develop Reference

Unable to execute jar file due to main manifest attribute missing

I have below project structure:
->bin
->lib
->resources
->src
->DemoFramework
->FirstDemo.java
In lib folder, I have an external jar that I need in my application. Its name is ext.jar. In resources, I have Manifest.txt file, whose content is given below.
Manifest-Version: 1.0
Class-Path: . lib/ext.jar
Main-Class: DemoFramework.FirstDemo
I am using below command to generate jar:
javac -cp ".;./lib/ext.jar" src/DemoFramework/*.java -d bin
Basically I am putting all class files into bin folder so that in final jar file, source code is not visible.
Then I am issuing below command:
jar cmf resources/Manifest.txt project.jar bin lib
The jar file is successfully created but when I run it, it says:
no main manifest attribute, in project.jar
I am confused about this error, no idea why it is happening.
Can you guys help me to sort it out?
Thanks.

Error: Could not find or load main class when trying to run jar file

I'm trying to create a JAR file of my Java code. There are four classes - A.java, B.java, C.java, and D.java. A.java has the main method. These are in a folder called src, and my manifest file is outside of src, and all of my .class files are in bin which is inside src. I created a MANIFEST.MF with the following contents:
Manifest-Version: 1.0
Main-Class: src/A
I then use the command jar cmf MANIFEST.MF A.jar src/bin/*.class src/GraphFile.txt src/ProblemA.txt src/ProblemB.txt (there are a few text files I need to include as well in my JAR file). Then, when I run java -jar A.jar ProblemA.txt GraphFile.txt (note that ProblemA.txt and GraphFile.txt are input files that my program accepts and uses), I get the following error:
Error: Could not find or load main class src.A
Caused by: java.lang.ClassNotFoundException: src.A
Can anyone explain what I am doing wrong or any steps I am missing? Unfortunately, I cannot post the actual code because this is for a class project, but I just need to get it compiled into a JAR file for submission! Thanks for any help.

"Could find or load main class" while running executable jar file in Java code

After converting my java program to executable jar file using commands in command prompt in windows 10,while executing jar file I am getting error:
Could find or load main class Combine.class" caused
by:java.lang.ClassNotFoundException:Combine.class
My jdk-11.0.1 has javamail api and excelapi.While executing I have set my classpath as:
classpath=%classpath%;C:\Program Files\Java\jdk-11.0.1\javamail_api\javax.mail-1.6.2.jar;C:\Program Files\Java\jdk-11.0.1\javamail_api\activation.jar;C:\Program Files\Java\jdk-11.0.1\jexcelapi\jxl.jar;.;
It was compiling and executing properly but after converting to executable jar file it is not running and giving above error.
Any help would be appreciated.
Thank you

The clue is in the exception message. It is trying to load a class with the name Combine.class. But the classes real name is Combine.
You have created the JAR file incorrectly.
echo Main-Class: Combine.class > manifest.txt
jar cmf manifest.txt FinalExecutable.jar Combine.class
If Combine is in the default package (i.e. it doesn't have a package statement) then the above should be:
echo Main-Class: Combine > manifest.txt
jar cmf manifest.txt FinalExecutable.jar Combine.class
If Combine is declared in package foo.bar, then the above should be.
echo Main-Class: foo.bar.Combine > manifest.txt
jar cmf manifest.txt FinalExecutable.jar foo/bar/Combine.class
and you need to be in the directory above the foo directory.
NB: the "Main-Class" attribute in the manifest must be a Java fully qualified class name, NOT a filename or file pathname.
It also should be noted that the CLASSPATH environment variable and the -cp argument will be ignored when you run a JAR using java -jar .... If your executable JAR depends on other JAR files, you should either combine them (to create a shaded JAR) or you should add a "Class-Path" attribute to the manifest; see https://docs.oracle.com/javase/tutorial/deployment/jar/downman.html
Finally, my advice would be to use a build tool (e.g. Maven) to compile your code, create the executable JAR file, etc rather than doing it by hand.

No main manifest attribute, jar file, Applet

When trying to open my exported project (jar file) I get an error message
No main manifest attribute, in file.jar.
My project is basically a simple class extended by Applet, but the file won't open.
My java is up to date and I've tried using the line in cmd
java -jar file.jar
in order to open it, but it still doesn't work.
What is the reason that the main class isn't recognized?
Thanks for the help!

Create a manifest file like this (manifest.mf)
Main-class: start.HelloWorld
Class-Path: /pathToYourExternalJars/XXXXX.jar /pathToYourExternalJars/XXXXX.jar
Here 'Main-class' is the starting point of your application (simply class which contains main method ) & 'Class-path' is for external jars which are included in your application (Optional)

Cannot create executable jar from Java Swing app successfully

I have made a Java Swing application and now I want to export it as an executable jar file. I have created the app in Eclipse, and it has the following structure :
where folder mysqlconnector contains also a jar file. So first I tried following the instructions in this link and created seo.jar, but when I try to execute it from the terminal by java -jar seo.jar I get an error :
Error: Could not find file connectionprops.properties
As the screenshot shows, I tried putting connectionprops.properties in main package, but the same problem remains.
Then I tried making a manifest file named manifest.mf with contents :
Main-Class: bin.main.MainClass //also tried Main-Class: MainClass
as the structure of my project is :
seo --> bin --> main --> MainClass.class
I placed the manifest.mf in folder seo and I gave the following command in the terminal :
jar -cvfm seo.jar manifest.mf *
but again when executing it from the terminal by java -jar seo.jar I get an error :
Error: Could not find or load main class bin.main.MainClass
What am I doing wrong? Should I change something in my project structure? Is there a problem that I have other jar files inside my project? How can I create the executable jar and execute it successfully?

The Manifest Main-Class attribute needs to receive the package path to your Main class. It doesn't matter what the structure of the project looks like, what matters is the fully qualified package name that you have inside the src/ folder. So in this case, main.MainClass is what you should write there.
Also, if you receive other errors when trying to read the connectionprops.properties in your program, try to open the file using
someObject.getClass().getResourceAsStream("connectionprops.properties")

bin.main is not a package name. You can't add this to manifest.mf.
You should add the package name only if you have the main class in the package. If your package is default then put only the main class.
Main-Class: MainClass