ThreadPoolTaskExecutor 異步配置

使用默認的 ThreadPoolExecutor.DiscardPolicy， 直接丟棄當前超出隊列的數據。

使用自定義的處理器，該處理器會阻塞地向BlockQueen 放數據，直到有剩餘空間可用（注意這可能導致很多線程處於 executor.getQueue().put(r) 方法線程等待中）。

/**
 * default executor is SimpleAsyncTaskExecutor
 * 配置參考 https://docs.spring.io/spring-boot/docs/2.3.0.RELEASE/reference/html/spring-boot-features.html#boot-features-task-execution-scheduling
 */
@Slf4j
@Configuration
@EnableAsync
public class AsyncConf {

    @Primary
    @Bean(name = "threadPoolTaskExecutor")
    public Executor threadPoolTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(4);
        executor.setMaxPoolSize(4);
        executor.setQueueCapacity(6000);
        executor.setKeepAliveSeconds(10);
        executor.setThreadNamePrefix("My Async Thread-");

        executor.setRejectedExecutionHandler(new RejectedExecutionHandlerImpl());
        executor.initialize();
        return executor;
    }

    public static class RejectedExecutionHandlerImpl implements RejectedExecutionHandler {

        @Override
        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
            try {
                //阻塞當前線程
                executor.getQueue().put(r);
            } catch (InterruptedException e) {
                throw new RejectedExecutionException("There was an unexpected InterruptedException whilst waiting to add a Runnable in the executor's blocking queue", e);
            }
        }
    }
}