Develop Reference

Can't figure out how to run my jar file "could not find or load main class"

I'm trying to create a jar file and run it using java -cp main.jar com.test.Foo.Main but I keep getting:
Error: Could not find or load main class com.test.Foo.Main
Caused by: java.lang.ClassNotFoundException: com.test.Foo.Main
This is my file structure. So I'm thinking the line in my Main.java should be package com.test.Foo correct?
I'm compiling my Main.java with javac Main.java which outputs a Main.class file. Afterward, I create a jar file using jar cfm main.jar META-INF/MANIFEST.MF Main.class and finally while I'm in the same directory as the jar file <root>/src/com/test/Foo/ I run java -cp main.jar com.test.Foo.Main and that's when I run into the above error. Any idea how I can run this file like this (and yes I need it to run with this command specifically)?
Main.java
package com.test.Foo;
public class Main {
public static void main (String args[]) {
System.out.println("I am com.test.Foo.Main");
}
}
META-INF/MANIFEST.MF
Manifest-Version: 1.0
Main-Class: com.test.Foo.Main
I tried using some of the options given in this popular SO question and nothing helped.

The picture you're showing in your question is your project structure not your jar structure.
When you create a jar file, the structure for that jar file might be
different with your source code folder structure.
Every IDE (such as eclipse, netbeans, IntelliJ) has a mechanism for creating JAR files. In your case when you open the created jar file (using zip apps like winrar) you should see something like this :
com
|
test
|
Foo
|
Main
META-INF
|
MANIFEST.MF
This should be the ordering of your files and folders, otherwise Java can not find your main class from MANIFEST.MF
Now to solve this problem:
Open your jar file using a zip application like winrar
check the folder structure residing inside your jar file as I draw
Fix it right away within the winrar or try to correct your project structure to produce the structure I mentioned.

The class is called com.test.Foo.Main you need to specify the full name in the command:
java -cp main.jar com.test.Foo.Main
or you can use the simpler
java -jar main.jar

Check your META-INF/MANIFEST.MF for the attribute of Manifest-Version: 1.0
This attribute must be there.
Edit:
You need to move to the source root src/ and issue below command to create a valid jar.
javac com/test/Foo/*.java
and, create the jar using,
jar cmf com/test/Foo/MANIFEST.MF main.jar com/test/Foo/*.class
The thing is, package structure should match with the folder structure apparently.

Can't find or load main class, in a .jar file

Been looking for around 2 hours for a solution to my problem, tried countless solutions and still the problem remains unsolved.
I have a game project with few packages; geometry, levels, decoration, and game. Inside the game package resides a gameRun.java
package game;
public class gameRun {
/**
* Program entry point.
* #param args the arguments for the levels
*/
public static void main(String args[]) {
... some code
}
}
and I have the following manifest file :
Main-Class: game.gameRun
Class-Path: someExternalGraphicTool.jar
//newline here
I compile my whole game using the following command : (the bin folder already exists).
javac -d bin src/geometry/*.java src/decoration/*.java src/levels/*.java src/game/*.java
I then turn my compiled classes into an executable .jar file using the command :
jar cvfm t.jar manifest.mf bin/geometry/*.class bin/decoration/*.class bin/levels/*.class bin/game/*.class
I then try to run my t.jar using :
java -jar t.jar
//or
java -cp .:t.jar game.gameRun
which both produce the error, "Error: Could not find or load main class game.gameRun"
However, when I unzip the jar file, inside the bin/game directory I can see a gameRun.class file and inside the META-INF\MANIFEST.MF file I can still see that the Main-Class is set to game.gameRun.
Note that I am working on a remote linux server, on a command line, and the jar file doesn't work even if I download it to my windows 10 machine.
What did I do wrong during this process ? Thanks for any help.

Your classes are in a wrong structure inside a jar file, because of the bin folder. My suggestion: pack it all into a jar starting in a bin folder.
Now when you extract your jar you will see 2 folders: META-INF and bin.
If you make the jar from bin folder you will see: META-INF and game, and it will work.
It doesn't work for you simply, because it can't find the main class, since it is inside the bin/game/YourClass.class, not in game/YourClass.class.
...\bin> jar cvfm t.jar manifest.mf geometry/*.class decoration/*.class levels/*.class game/*.class
And then just:
...\bin> java -jar t.jar

Command line java error: Could not find or load main class

I'm trying to run a project from the command line (Ubuntu 14.04). The main class is called Demo, and I have a Demo.java, a Demo.class, and a Demo$1.class all in the same directory (I know it would be better to seperate them).
I wrote my own Manifest file, MANIFEST.MF, which just looks like this:
Main-Class:Demo
I made sure to end it with a newline.
Next, I want to create my .jar file. I did so with this command:
jar -cfm example.jar MANIFEST.MF *.class
Then, I try to run my project like so:
java -Djava.library.path=/path/to/dependencies -jar example.jar
I seem to get the following error no matter what I try:
Error: Could not find or load main class Demo
I've actually never compiled/run a Java project from the command line before, it's possible I'm making a stupid mistake and just can't figure it out. Any help is appreciated!
EDIT: Here are the contents of example.jar, according to vim:
" zip.vim version v27
" Browsing zipfile /home/ellen/bendersexample2/src/bendersexample/example.jar
" Select a file with cursor and press ENTER
META-INF/
META-INF/MANIFEST.MF
AnnotatedBenders.class
Demo$1.class
Demo.class
Demo$ModelType.class
ManualBenders$1.class
ManualBenders$BendersCallback.class
ManualBenders.class
Model.class
Problem.class
Solution.class
Solution$Verbosity.class
StandardModel.class
Here are the contents of the META-INF/MANIFEST.MF which is in the jar:
Manifest-Version: 1.0
Created-By: 1.8.0_161 (Oracle Corporation)
Main-Class: Demo
UPDATE: Here are the interesting parts of Demo.java:
package bendersexample;
public final class Demo {
/* Some functions */
public static void main(final String[] args) {
/* Some code */
}
}
I changed my MANIFEST.MF to the following:
Main-Class:bendersexample.Demo
And re-generated the example.jar file. I still get the following:
Error: Could not find or load main class bendersexample.Demo
Could there be an issue with how I generate my class files?
To generate the class files initially, I did the following:
javac -classpath .:/opt/ibm/ILOG/CPLEX_Studio_Community128/cplex/lib/cplex.jar *.java
Please let me know what else I should try! Thank you

The problem was just that had the Manifest in the /bendersexample folder and the was creating the .jar in this folder as well! I just needed to move that stuff into the parent directory and everything worked fine!
The final Manifest file used bendersexample.Demo as the Main-Class, and the jar was created and run from /bendersexample 's parent directory.
If anyone runs into this problem I would recommend taking a look at your project's structure before trying anything else, because this turned out to be a very easy fix!

Using JAR Files

So I'm still a noob in Java and I'm experimenting around with a few things.
I recently created a .jar file for my class using jar cvf <name>.jar <source files> and then used that jar to compile my driver class (javac -cp <name>.jar Driver.java) though how do I now run that class using the jar?
I've tried the following 2 commands:
java Driver and,
java -cp <name>.jar Driver.
The first gives me a NoClassDefFoundError for the class used, whereas the latter just gave me a single line error.
Error: Could not find or load man class Driver
What am I doing wrong? Is it possible I'm confusing this for something else?
I'm trying to do as much as I can without the use of any IDE.

You should put jar file and compiler output into classpath and specify main class:
java -classpath "<name.jar>;classes" Driver
EDIT (thanks to Kayaman):
If you are running command from linux/unix you have to use ":" as separator (in Windows works ";"). "classes" is a path to folder containing compiler output.

When creating an executable jar ( jar which contain a class with the main method) you should tell the jar which is the mainClass to be executed and for that you should create a file called 'Manifest.mf'.
The file should contain this:
Main-Class: MyPackage.MyClass
And when creating the jar you should use this to include your manifest:
jar cfm MyJar.jar Manifest.mf MyPackage/*.class
And for launching your jar :
java -jar MyJar.jar

Bundling JAR dependencies with executable JAR (Über JAR) from command line

I'm trying to create an executable jar from the command line. The main class in the JAR has dependencies that i have packaged into another plain JAR file.
I want to package the dependency JAR together with the executable JAR in order to have a single JAR file to ship.
What i have tried so far is the following:
The dependency Hello.class file has the mock code:
public class Hello {
public String getHello() {
return "Well hello there!!";
}
}
I have packaged class file into hello.jar using:
jar cvfM hello.jar Hello.class
The hello.jar content is now:
hello.jar -+- Hello.class
Now i have the main class with the mock code:
public class Main {
public static void main(String[] args) {
System.out.println(new Hello().getHello());
}
}
I then create a manifest file manifest.txt with the following content:
Main-Class: Main
Class-Path: hello.jar
I now create the executable JAR using:
jar cvfm main.jar manifest.txt Main.class hello.jar
The main.jar content is now:
main.jar -+- Main.class
|
+- hello.jar
|
+- META-INF -+- MANIFEST.MF
Running the executable JAR using:
java -jar main.jar
I get a class loader error for the Hello class dependency. I understand that this is because the class loader looks for hello.jar in the same path as main.jar. So when i put a copy of hello.jar alongside main.jar i am able to run it.
What do i need to do in order to be able to run main.jar with hello.jar inside of it?
I know that you will ask: "why is he trying to do it this way?". I know that ppl mostly use Eclipse, Ant, Maven or other tools to do this. But please just humor me :)

Your approach is completely wrong unfortunately.
There is no "normal" way to place a jar inside of another jar. So your hello.jar has nothing to do inside of main.jar! The point is the "normal" classloader wont look for jar files inside of jars, hence you get the class not found error.
However: if you want desparetly to do that, then google for "OneJar" and go to http://one-jar.sourceforge.net/

There's no easy way to do this. That is, you are going to have to write your own classloader if you want to nest jars inside a jar.
There are several products out there that already support this for you. One-Jar is one of them that I've used with a lot of success -- can easily ant script it.
Here is an interesting SO discussion on the whole topic --
Easiest way to merge a release into one JAR file

Well, I believe you may be facing a jar generation bug. Check out this link, it might enlight you.
A teaser:
As far as I aware, and based on my own attempts, there's no
way to specify a Class-Path that makes the class loader
look in embedded jar files. See the preceeding paragraph
for a description.
Therefore, you may check one of the following links:
classpath-including-jar-within-a-jar, java-easiest-way-to-merge-a-release-into-one-jar-file
Cheers!