Java实现异步的几种方式
[*]普通线程实现异步，但频繁创建、销毁线程比较耗资源，所以一般交给线程池执行
//创建需要异步执行的逻辑
public class AsyncThread implements Runnable{
@Override
public void run() {
System.out.println("异步线程开始");
long start = System.currentTimeMillis();
try {
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
long end = System.currentTimeMillis();
System.out.println("异步线程：" + Thread.currentThread().getName() + "结束，耗时：" + (end - start));
}
}
//在业务中进行调用
@GetMapping("/thread")
public String asyncThread(){
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(3, 3, 5, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(10), new ThreadPoolExecutor.AbortPolicy());
long start = System.currentTimeMillis();
//自己的业务代码。。。
AsyncThread asyncThread = new AsyncThread();
threadPool.execute(asyncThread);
long end = System.currentTimeMillis();
return "返回,耗时:" + (end - start);
}结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171324069-285443538.png
[*]Future异步
和普通线程实现异步区别不大，只是使用Future是要获取执行后的返回值
//创建具有返回值的任务
public class CallableThread implements Callable {
@Override
public String call() throws Exception {
long start = System.currentTimeMillis();
StopWatch stopWatch = new StopWatch();
stopWatch.start();
System.out.println("callable任务开始执行:" + start);
TimeUnit.SECONDS.sleep(2);
System.out.println();
stopWatch.stop();
System.out.println("stopWatch.prettyPrint------");
System.out.println(stopWatch.prettyPrint());
System.out.println("stopWatch.shortSummary------");
System.out.println(stopWatch.shortSummary());
System.out.println("stopWatch.getTotalTimeMillis------");
System.out.println(stopWatch.getTotalTimeMillis());
return "call执行结束 ";
}
}
//在业务中进行调用
public String threadFuture(){
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(3, 3, 5, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(10), new ThreadPoolExecutor.AbortPolicy());
long start = System.currentTimeMillis();
CallableThread callableThread = new CallableThread();
Future<String> submit = threadPool.submit(callableThread);
try {
//在获取返回值时会阻塞主线程
String s = "";
s = submit.get();
System.out.println(s);
} catch (Exception e) {
System.out.println("线程运行发生错误" + e.getMessage());
throw new RuntimeException(e);
}
long end = System.currentTimeMillis();
return "接口返回,耗时:" + (end - start);
}结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171400685-1459024203.png
[*]Spring的@Async异步
[*]使用@Async注解实现异步的前提是需要在启动类上标注@EnableAsync来开启异步配置
[*]配置线程池（@Async默认情况下用的是SimpleAsyncTaskExecutor线程池，该线程池不是真正意义上的线程池，使用此线程池无法实现线程重用，每次调用都会新建一条线程。若系统中不断的创建线程，最终会导致系统占用内存过高，引发OutOfMemoryError错误）
/**
* 线程池配置，可以配置多个线程池
* @Async注解，默认使用系统自定义线程池，可在项目中设置多个线程池，在异步调用的时候，指明需要调用的线程池名称
* 比如：@Async("线程池1")
*/
@Configuration
public class ExecutorConfig {
/**
* 自定义线程池
*/
@Bean("myExecutor")
public Executor taskExecutor(){
System.out.println("系统最大线程数:" + Runtime.getRuntime().availableProcessors());
ThreadPoolTaskExecutor threadPoolTaskExecutor = new ThreadPoolTaskExecutor();
threadPoolTaskExecutor.setCorePoolSize(8);//核心线程数
threadPoolTaskExecutor.setMaxPoolSize(16);//最大线程数
threadPoolTaskExecutor.setQueueCapacity(1000);//配置队列容量
threadPoolTaskExecutor.setKeepAliveSeconds(60);//空闲线程存活时间
threadPoolTaskExecutor.setThreadNamePrefix("myExecutor-");//线程名字前缀
return threadPoolTaskExecutor;
}
}
[*]编写异步方法的逻辑，异步方法所在的类需要被Spring管理
@Service
public class AsyncServiceImpl implements AsyncService {
@Override
@Async("myExecutor")
public void sendMsg() {
System.out.println("进入异步方法");
System.out.println("当前线程名称：" + Thread.currentThread().getName());
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println("异步方法执行完成");
}
/**
* 具有返回值的异步方法，返回类型为Future,返回时new 一个AsyncResult对象，其中参数为返回的内容
* @return
*/
@Override
@Async("myExecutor")
public Future<String> sendMsgFuture() {
System.out.println("进入future异步方法");
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
return new AsyncResult<>("future异步方法执行完成");
}
}
[*]在业务逻辑中调用
@GetMapping("/asyncMethod")
public String asyncMethod(){
System.out.println("aaa");
System.out.println("调用异步方法");
asyncService.sendMsg();
System.out.println("bbb");
return "asyncMethod方法返回";
}调用没有返回值的异步方法结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171436436-2081307499.png
@GetMapping("/asyncFutureMethod")
public String asyncFutureMethod(){
System.out.println("aaa");
Future<String> stringFuture = asyncService.sendMsgFuture();
System.out.println("bbb");
try {
System.out.println(stringFuture.get());//get方法会阻塞主线程
} catch (Exception e) {
throw new RuntimeException(e);
}
return "asyncfutureMethod方法返回";
}调用有返回值的异步方法结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171512568-86308802.png
[*]Spring的ApplicationEvent事件实现异步
[*]定义事件，继承ApplicationEvent类
public class MessageEvent extends ApplicationEvent {
@Getter
private String message;
public MessageEvent(Object source, String message) {
super(source);
this.message = message;
}
}
[*]定义监听器（需要被Spring管理）
使用@EventListener注解写在方法上定义一个监听器，即事件被触发时执行的方法(默认是同步执行，可以使用@Async注解标注为异步执行)，支持多个监听器监听同一个事件。
@Component
public class MessageEventHandler {
//@Async
@EventListener
public void handleLoginEvent(LoginEvent event){
System.out.println("接受到LoginEvent事件");
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println(event.getUsername());
System.out.println("LoginEvent事件处理完成");
}
//@Async
@EventListener
public void handleMessageEvent(MessageEvent event){
System.out.println("接受到MessageEvent事件");
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println(event.getMessage());
System.out.println("MessageEvent事件处理完成");
}
}
[*]定义事件发布者(触发事件的)（需要被Spring管理）
实现ApplicationEventPublisherAware接口
@Component
public class EventPublisher implements ApplicationEventPublisherAware {
private ApplicationEventPublisher publisher;
@Override
public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
this.publisher = applicationEventPublisher;
}
public void publish(ApplicationEvent event){
if (event instanceof MessageEvent){
System.out.println("开始发布MessageEvent事件:" + ((MessageEvent) event).getMessage());
} else if (event instanceof LoginEvent) {
System.out.println("开始发布LoginEvent事件:" + ((LoginEvent) event).getUsername());
}
//发布事件
publisher.publishEvent(event);
System.out.println("事件发布结束");
}
}
[*]业务代码执行时触发事件
@GetMapping("/pubEvent")
public String publishEvent(){
System.out.println("业务逻辑开始");
eventPublisher.publish(new MessageEvent(this,"testEvent"));
System.out.println("业务逻辑结束");
return "发布成功";
}执行结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171529429-2146982998.png
由控制台打印可以发现现在事件监听器方法的执行是同步的，如果需要异步执行，在监听器方法上加个@Async注解即可，但使用Async注解的前提是在启动类上标注@EnableAsync注解来开启异步配置
使用@Async注解后执行结果：https://img2023.cnblogs.com/blog/2908974/202312/2908974-20231214171541963-1420358165.png
可以看到监听器中的打印在最后了，证明是异步执行的
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