Question

I am new to Java and learning how to export applications to .jar files. I made a simple Java application in Eclipse with a few classes based on the tutorial from Eclipse and Java for Total Beginners.

When I run my application via Run -> Run in Eclipse, my application runs without exceptions. However, when I got to File -> Export and export my application into a .jar file and then execute

java myLibrary.jar

in my Mac terminal, I get this output from standard error.

Exception in thread "main" java.lang.NoClassDefFoundError: myLibrary/jar

Caused by: java.lang.ClassNotFoundException: myLibrary.jar
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

What does this mean? How am I missing classes? I tried checking and unchecking items to export. For instance, I tried including my JUnit tests to no avail.

Answer 1

In the terminal go to the directory that contains all your class files.

jar cmf MANIFEST.MF myLibrary.jar *

Then if the jar is created successfully you can run it by:

java -jar myLibrary.jar

The MANIFEST.MF file should contain at the very least:

Main-Class: myLibrary

Where myLibrary is the class that contains your main function.