Specifies the java.util.Executor instance to use when invoking asynchronous methods. If not provided, an instance of org.springframework.core.task.SimpleAsyncTaskExecutor will be used by default. Specifies the org.springframework.scheduling.TaskScheduler or java.util.ScheduledExecutorService instance to use when invoking scheduled methods. If no reference is provided, a TaskScheduler backed by a single thread scheduled executor will be used.