Getting ClassNotFound Exception when executing jar

Question

• Am using IntelliJ 12.0.4 Community Edition.
• I created a Java console app called DB with main class name of DB.
• I packaged it into an executable jar file called DB.jar.
• In that app I connect to an Oracle DB using JDBC.

• I packaged the necessary JDBC jar files into the DB.jar via the Intellij's Project Structure (Modules, Library)

• When I execute the app from within IntelliJ it runs successfully

• If I copy DB.jar to some directory and execute it via "java -jar DB.jar" I get an ClassNotFound exception on oracle.jdbc.driver.OracleDriver
• I looked in DB.jar and the jdbc jar files (ojdbc6.jar, ojdbc14.jar) are in DB.jar
• Any thoughts?

Answer 1

Jars in an executable jar are not on the classpath, typically.

You can put them in the same folder as DB.jar and do:

java -cp DB.jar;ojdbc6.jar;ojdbc14.jar <MainClass goes here>

and that should run it.

You could also put the Class-Path entry in the Manifest.MF file inside your jar to reference other jars relative to the location of DB.jar in the computer's file system. Reference the two other jar files and then you can do java -jar DB.jar <MainClass goes here> (assuming the two jars are in the right place.

There is some discussion here about the general frustration about not being able to do what you want to do (and what many others have wanted for years).

Classpath including JAR within a JAR

Explain about Main Class

When you run a java application from the command line, there is some class where the execution starts. It will look something like this:

package com.mycompany.app;

public class StartHere {

    public static void main(String[] args) {
        // Your code goes here ...
    }
}

If this example was the class where your application starts you would use a command line this to start it. This assumes you have the StartHere class in the right package location in a jar on the classpath:

java -cp DB.jar;ojdbc6.jar;ojdbc14.jar com.mycompany.app.StartHere

Notice that this allows you to have multiple applications in the same jar. Just make multiple classes with a main() method and run them with different starting classes shown on the command line.