Error 500: java.lang.NoClassDefFoundError: packageName/className

 The NoClassDefFoundError indicates that the classloader , which is responsible for dynamically loading classes, cannot find the .class file for the class that you're trying to use. The definition of a class can be requested during a method call , or while creating a new instance using a new expression. NoClassDefFoundError means that the class is present in the classpath at Compile time, but it doesn't exist in the classpath at Runtime. After you compile your code, you end up with .class files for each class in your program. These binary files are the bytecode that Java interprets to execute your program.