Question

I’m writing a short utility that performs a short task on a remote Oracle instance. The utility uses the Oracle jdbc driver found in ojdbc6.jar.

The Oracle jar is properly included in my classpath. When I export my project to a jar and run the jar on the command line using “java -jar “, I get:

Exception in thread "main" java.lang.ClassNotFoundException: oracle.jdbc.OracleDriver
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at java.lang.Class.forName0(Native Method)

After moving the Oracle jar into the same directory as my runnable jar file, I changed my Manifest file to include the the Oracle jar in the classpath. This fixed the problem, and my jar ran fine.

Can anyone explain why including the Oracle jar in my classpath didn’t solve the problem, and why editing the Manifest file did?

Thanks!

Answer 1

From Sun (Oracle) documentation for the java -jar command:

Execute a program encapsulated in a JAR file. The first argument is
the name of a JAR file instead of a startup class name. In order for
this option to work, the manifest of the JAR file must contain a line
of the form Main-Class: classname. Here, classname identifies the
class having the public static void main(String[] args) method that
serves as your application’s starting point. See the Jar tool
reference page and the Jar trail of the Java Tutorial for information
about working with Jar files and Jar-file manifests. When you use this
option, the JAR file is the source of all user classes, and other user
class path settings are ignored.