目录
Spring Boot多线程
Spring Boot多线程
1.配置线程池
Spring Boot应用中需要添加@EnableAsync注解,来开启异步调用,一般还会配置一个线程池,异步的方法交给特定的线程池完成,如下:
@Configuration
@EnableAsync
public class AsyncConfiguration {
@Bean("doSomethingExecutor")
public Executor doSomethingExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
// 核心线程数:线程池创建时候初始化的线程数
executor.setCorePoolSize(10);
// 最大线程数:线程池最大的线程数,只有在缓冲队列满了之后才会申请超过核心线程数的线程
executor.setMaxPoolSize(20);
// 缓冲队列:用来缓冲执行任务的队列
executor.setQueueCapacity(500);
// 允许线程的空闲时间60秒:当超过了核心线程之外的线程在空闲时间到达之后会被销毁
executor.setKeepAliveSeconds(60);
// 线程池名的前缀:设置好了之后可以方便我们定位处理任务所在的线程池
executor.setThreadNamePrefix("do-something-");
// 缓冲队列满了之后的拒绝策略:由调用线程处理(一般是主线程)
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
executor.initialize();
return executor;
}
}
2.异步方法(@Async)
使用的方式非常简单,在需要异步的方法上加@Async注解
@Slf4j
@Service
public class AsyncService {
// 指定使用beanname为doSomethingExecutor的线程池
@Async("doSomethingExecutor")
public String doSomething(String message) {
log.info("do something, message={}", message);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
log.error("do something error: ", e);
}
return message;
}
}
@RestController
public class AsyncController {
@Autowired
private AsyncService asyncService;
@GetMapping("/open/something")
public String something() {
int count = 10;
for (int i = 0; i < count; i++) {
asyncService.doSomething("index = " + i);
}
return "success";
}
}
访问:http://127.0.0.1:8080/open/something
注意事项
@Async注解会在以下几个场景失效,也就是说明明使用了@Async注解,但就没有走多线程
(1)异步方法使用static关键词修饰
(2)异步类不是一个Spring容器的bean(一般使用注解@Component和@Service,并且能被Spring扫描到)
(3)SpringBoot应用中没有添加@EnableAsync注解
(4)在同一个类中,一个方法调用另外一个有@Async注解的方法,注解不会生效。原因是@Async注解的方法,是在代理类中执行的
注意:异步方法使用注解@Async的返回值只能为void或者Future及其子类,当返回结果为其他类型时,方法还是会异步执行,但是返回值都是null
获取异步方法返回值
当异步方法有返回值时,如何获取异步方法执行的返回结果呢?这时需要异步调用的方法带有返回值CompletableFuture
CompletableFuture:对Future的增强,Future只能处理简单的异步任务,而CompletableFuture可以将多个异步任务进行复杂的组合
@Slf4j
@Service
public class AsyncService {
@Async("doSomethingExecutor")
public CompletableFuture<String> doSomething1(String message) throws InterruptedException {
log.info("do something1: {}", message);
Thread.sleep(1000);
return CompletableFuture.completedFuture("do something1: " + message);
}
@Async("doSomethingExecutor")
public CompletableFuture<String> doSomething2(String message) throws InterruptedException {
log.info("do something2: {}", message);
Thread.sleep(1000);
return CompletableFuture.completedFuture("; do something2: " + message);
}
@Async("doSomethingExecutor")
public CompletableFuture<String> doSomething3(String message) throws InterruptedException {
log.info("do something3: {}", message);
Thread.sleep(1000);
return CompletableFuture.completedFuture("; do something3: " + message);
}
}
@RestController
public class AsyncController {
@Autowired
private AsyncService asyncService;
@SneakyThrows
@ApiOperation("异步 有返回值")
@GetMapping("/open/somethings")
public String somethings() {
CompletableFuture<String> createOrder = asyncService.doSomething1("create order");
CompletableFuture<String> reduceAccount = asyncService.doSomething2("reduce account");
CompletableFuture<String> saveLog = asyncService.doSomething3("save log");
// 等待所有任务都执行完
CompletableFuture.allOf(createOrder, reduceAccount, saveLog).join();
// 获取每个任务的返回结果
String result = createOrder.get() + reduceAccount.get() + saveLog.get();
return result;
}
}