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

Question

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

Is your own jar in the classpath ? Also please add the full command line you are using. — Arnaud, Jan 29 '19 at 13:11
simplest solution, make a runnable jar (it will include everything needed). the issue is that your jar doesn't include those libraries — aran, Jan 29 '19 at 13:22
echo Main-Class: Combine.class > manifest.txt jar cmf manifest.txt FinalExecutable.jar Combine.class I am using these commands to convert into executable file — korupolu prasanna, Jan 29 '19 at 13:25
View your jar file in archive explorer to debug your mainfest. — Vishwa Ratna, Jan 29 '19 at 13:49
Also: don't forget to put the full name of the class, ie with the package if there is any — Prim, Jan 29 '19 at 14:06

Stephen C · Answer 1 · 2020-12-11T08:01:06.870

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.

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

1 Answers1