NoClassDefFoundError exception in your Maven project

After you have added a new dependency, you could have exception like this:

NetBeans error:

--- exec-maven-plugin:1.2.1:exec (default-cli) @ integration ---
java.lang.NoClassDefFoundError: path/to/the/class/ClassName
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
    at java.lang.Class.getMethod0(Class.java:3018)
    at java.lang.Class.getMethod(Class.java:1784)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: package.ClassName
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 7 more

IntellijIdea error:

Exception in thread "main" java.lang.NoClassDefFoundError: ClassName
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:122)
Caused by: java.lang.ClassNotFoundException: com.thoughtworks.xstream.converters.Converter
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 3 more

The reason is possibly a missed compile-time scope of the library, you have added recently:        <dependency>
            <groupId>com.thoughtworks.xstream</groupId>
            <artifactId>xstream</artifactId>
            <version>1.4.8</version>
            <scope>compile</scope>
        </dependency>