1. @Async源码探究 1.1. 上代码 @SpringBootApplication @EnableAsync public class SpringbootLearnApplication { public static void main(String[] args) { SpringApplication.run(SpringbootLearnApplication.class, args); } } @Service public class CreatingThread08Service { @Async public void call(CountDownLatch countDownLatch) { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + " is running"); countDownLatch.countDown(); System.out.println(Thread.currentThread().getName() + " is over"); } } @RunWith(SpringRunner.class) @SpringBootTest public class SpringbootLearnApplicationTests { @Autowired private CreatingThread08Service creatingThread08Service; private int count = 4; private CountDownLatch countDownLatch = new CountDownLatch(count); @Test public void contextLoads() { StopWatch stopwatch = new StopWatch("async test"); stopwatch.start(); for (int i = 0; i < count; i++) { creatingThread08Service.call(countDownLatch); } try { countDownLatch.await(); } catch (InterruptedException e) { e.printStackTrace(); } stopwatch.stop(); System.out.println(stopwatch.prettyPrint()); } }
结果
task-2 is running task-2 is over task-4 is running task-4 is over task-1 is running task-1 is over task-3 is running task-3 is over StopWatch 'async test': running time (millis) = 1018 ----------------------------------------- ms % Task name ----------------------------------------- 01018 100% 1.2. 提问 1.2.1. 加了该注解的方法，如果同时被调用n次，难道会创建n个线程？通过debugger源码找到如下信息，为它默认线程池设置属性
我们把运行数量加大到count=20
结果
task-1 is running task-1 is over task-8 is running task-8 is over task-5 is running task-5 is over task-3 is running task-3 is over task-4 is running task-4 is over task-7 is running task-7 is over task-2 is running task-2 is over task-6 is running task-6 is over task-1 is running task-1 is over task-8 is running task-3 is running task-3 is over task-5 is running task-5 is over task-8 is over task-4 is running task-6 is running task-6 is over task-7 is running task-7 is over task-2 is running task-2 is over task-4 is over task-5 is running task-1 is running task-8 is running task-8 is over task-1 is over task-3 is running task-3 is over task-5 is over StopWatch 'async test': running time (millis) = 3021 ----------------------------------------- ms % Task name ----------------------------------------- 03021 100%可以看出，如截图一致，它的运行核心执行线程数为8，且队列数很大，所以几乎不会再创建新的线程数，我特意sleep了1秒，20个任务，足够该线程池运行3遍，所以最大延迟3秒多
1.3. 那么核心线程数这个值能够变吗？可以，通过application.properties中修改spring.task.execution.pool.core-size=20的值，比如我现在改成20，那么打印结果如下
task-1 is running task-9 is running task-12 is running task-15 is running task-17 is running task-11 is running task-11 is over task-1 is over task-10 is running task-10 is over task-8 is running task-8 is over task-6 is running task-6 is over task-4 is running task-4 is over task-7 is running task-7 is over task-5 is running task-3 is running task-3 is over task-20 is running task-20 is over task-17 is over task-19 is running task-19 is over task-2 is running task-2 is over task-18 is running task-18 is over task-15 is over task-16 is running task-16 is over task-12 is over task-14 is running task-14 is over task-13 is running task-13 is over task-9 is over task-5 is over StopWatch 'async test': running time (millis) = 1020 ----------------------------------------- ms % Task name ----------------------------------------- 01020 100%所有线程只执行一遍，最大延迟就1秒多了
1.4. 总结使用该注解，会创建默认核心线程为8的线程池，它的很多属性是可以通过配置设置的，如下
spring.task.execution.pool.core-size=10 spring.task.execution.thread-name-prefix=mytask- spring.task.execution.pool.queue-capacity=10 spring.task.execution.pool.max-size=20 spring.task.execution.pool.keep-alive=60s spring.task.execution.pool.allow-core-thread-timeout=true根据业务需求设置合理的属性值，就相当于spring给你创建了线程池了