Spring boot. How to Create TaskExecutor with Annotation?

UPDATE: as of Spring Boot 2.1, there is no need to create the ThreadPoolTaskExecutor through code, since ThreadPoolTaskExecutor is the default and can be completely configured using properties prefixed with spring.task.execution.

So, steps:

1. use @EnableAsync in a @Configuration-annotated class,
2. annotate one or more methods with @Async
3. optionally override the default ThreadPoolTaskExecutor config with properties

Properties example:

spring.task.execution.pool.core-size=1
spring.task.execution.pool.max-size=20
spring.task.execution.pool.keep-alive=120s
spring.task.execution.pool.queue-capacity=1000
spring.task.execution.shutdown.await-termination=true
spring.task.execution.shutdown.await-termination-period=5m
spring.task.execution.thread-name-prefix=async-executor-
spring.task.execution.pool.allow-core-thread-timeout=false

If more customization is required, one can also implement the TaskExecutorCustomizer interface, for example (in kotlin):

@Component
class AsyncExecutorCustomizer : TaskExecutorCustomizer {
    override fun customize(taskExecutor: ThreadPoolTaskExecutor?) {
        taskExecutor?.let { executor ->
            executor.setRejectedExecutionHandler(ThreadPoolExecutor.CallerRunsPolicy())
        }
    }
}

First – let’s go over the rules – @Async has two limitations:

• it must be applied to public methods only
• self-invocation – calling the async method from within the same class – won’t work

So your processPage() method should be in separate class

Add a @Bean method to your Spring Boot application class:

@SpringBootApplication
@EnableAsync
public class MySpringBootApp {

    @Bean
    public TaskExecutor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(25);
        return executor;
    }

    public static void main(String[] args) {
        // ...
    }
}

See Java-based container configuration in the Spring Framework reference documentation on how to configure Spring using Java config instead of XML.

(Note: You don't need to add @Configuration to the class because @SpringBootApplication already includes @Configuration).