Maven & Java: The parameters ‘mainClass’ for goal org.codehaus.mojo:exec-maven-plugin:1.2.1:java are missing or invalid

“configuration” must go outside “executions”, like this: <plugins> <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <version>1.2.1</version> <executions> <execution> <goals> <goal>java</goal> </goals> </execution> </executions> <configuration> <mainClass>com.emilio.App</mainClass> </configuration> </plugin> </plugins>