In the absence of an `Executor` bean in the context, Spring Boot auto-configures a `ThreadPoolTaskExecutor` with sensible defaults that can be automatically associated to asynchronous task execution (`@EnableAsync`) and Spring MVC asynchronous request processing.
If you have defined a custom `Executor` in the context, regular task execution (that is `@EnableAsync`) will use it transparently but the Spring MVC support will not be configured as it requires an `AsyncTaskExecutor` implementation (named `applicationTaskExecutor`).
Depending on your target arrangement, you could change your `Executor` into a `ThreadPoolTaskExecutor` or define both a `ThreadPoolTaskExecutor` and an `AsyncConfigurer` wrapping your custom `Executor`.
The auto-configured `TaskExecutorBuilder` allows you to easily create instances that reproduce what the auto-configuration does by default.
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The thread pool uses 8 core threads that can grow and shrink according to the load.
Those default settings can be fine-tuned using the `spring.task.execution` namespace, as shown in the following example:
The thread pool uses one thread by default and its settings can be fine-tuned using the `spring.task.scheduling` namespace, as shown in the following example:
Both a `TaskExecutorBuilder` bean and a `TaskSchedulerBuilder` bean are made available in the context if a custom executor or scheduler needs to be created.