<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
  <version>2023.0.1.0</version>
</dependency>

spring:
  application:
    name: dynamic-threadpool-demo
  cloud:
    nacos:
      config:
        server-addr: 127.0.0.1:8848
        file-extension: yaml
        refresh-enabled: true

threadpool:
  coreSize: 5
  maxSize: 20
  queueCapacity: 100
  keepAliveSeconds: 60

@Component
@RefreshScope
@ConfigurationProperties(prefix = "threadpool")
public class ThreadPoolProperties {
    private int coreSize;
    private int maxSize;
    private int queueCapacity;
    private long keepAliveSeconds;
    // getters & setters
}

@Component
public class DynamicThreadPoolManager {
    private volatile ThreadPoolExecutor executor;
    private final ThreadPoolProperties props;

    public DynamicThreadPoolManager(ThreadPoolProperties props) {
        this.props = props;
        this.executor = createExecutor(props);
    }

    @NacosConfigListener(dataId = "${spring.application.name}.yaml", timeout = 5000)
    public void onChange(String newContent) throws JsonProcessingException {
        ThreadPoolProperties updated = new ObjectMapper()
            .readValue(newContent, ThreadPoolProperties.class);
        executor.setCorePoolSize(updated.getCoreSize());
        executor.setMaximumPoolSize(updated.getMaxSize());
        executor.setKeepAliveTime(updated.getKeepAliveSeconds(), TimeUnit.SECONDS);
        // 如果需要修改隊列容量，則重建 executor
    }

    private ThreadPoolExecutor createExecutor(ThreadPoolProperties p) {
        return new ThreadPoolExecutor(
            p.getCoreSize(), p.getMaxSize(),
            p.getKeepAliveSeconds(), TimeUnit.SECONDS,
            new LinkedBlockingQueue<>(p.getQueueCapacity()),
            r -> new Thread(r, "dyn-pool-" + UUID.randomUUID()),
            new ThreadPoolExecutor.CallerRunsPolicy()
        );
    }

    public void submit(Runnable task) {
        executor.execute(task);
    }
}

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner demo(DynamicThreadPoolManager manager) {
        return args -> {
            for (int i = 0; i < 50; i++) {
                int id = i;
                manager.submit(() -> {
                    System.out.println(Thread.currentThread().getName() + " - Task " + id);
                });
            }
        };
    }
}