Overriding a class file from a library JAR in a Java web app

Question

In my Java web app, I have these files:

/WEB-INF/classes/com/example/Foo.class
/WEB-INF/lib/example.jar <-- contains the class "com.example.Foo"

Will the class defined in the classes directory be used instead of the class defined in example.jar?

Thanks.

Answer 1

The answer depends upon your container, it is container dependent. In general, /WEB-INF/classes is preferred to classes in a jar file in WEB-INF/lib.

For Tomcat, the order is the following:

Therefore, from the perspective of a web application, class or resource loading looks in the following repositories, in this order:

1. Bootstrap classes of your JVM
2. System class loader classes
3. /WEB-INF/classes of your web application
4. /WEB-INF/lib/*.jar of your web application
5. Common class loader classes

But if you're using a different container, you need to consult the documentation for that server.