Java实现异步调用
一、创建线程
@Test
public void test0() throws Exception {
System.out.println("main函数开始执行");
Thread thread=new Thread(new Runnable() {
@Override
public void run() {
System.out.println("===task start===");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("===task finish===");
}
});
thread.start();
System.out.println("main函数执行结束");
}
二、Future
jdk8之前的实现方式,在JUC下增加了Future,从字面意思理解就是未来的意思,但使用起来却着实有点鸡肋,并不能实现真正意义上的异步,获取结果时需要阻塞线程,或者不断轮询。
@Test
public void test1() throws Exception {
System.out.println("main函数开始执行");
ExecutorService executor = Executors.newFixedThreadPool(1);
Future<Integer> future = executor.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
System.out.println("===task start===");
Thread.sleep(5000);
System.out.println("===task finish===");
return 3;
}
});
//这里需要返回值时会阻塞主线程,如果不需要返回值使用是OK的。倒也还能接收
//Integer result=future.get();
System.out.println("main函数执行结束");
System.in.read();
}
三、CompletableFuture
使用原生的CompletableFuture实现异步操作,加上对lambda的支持,可以说实现异步任务已经发挥到了极致。
@Test
public void test2() throws Exception {
System.out.println("main函数开始执行");
ExecutorService executor = Executors.newFixedThreadPool(2);
CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
@Override
public Integer get() {
System.out.println("===task start===");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("===task finish===");
return 3;
}
}, executor);
future.thenAccept(e -> System.out.println(e));
System.out.println("main函数执行结束");
}
四、Spring的Async注解
使用spring实现异步需要开启注解,可以使用xml方式或者java config的方式。
xml方式: <task:annotation-driven />
<task:annotation-driven executor="executor" />
<task:executor id="executor"
pool-size="2" 线程池的大小
queue-capacity="100" 排队队列长度
keep-alive="120" 线程保活时间(单位秒)
rejection-policy="CALLER_RUNS" 对拒绝的任务处理策略 />
java方式:
@EnableAsync
public class MyConfig {
@Bean
public TaskExecutor executor(){
ThreadPoolTaskExecutor executor=new ThreadPoolTaskExecutor();
executor.setCorePoolSize(10); //核心线程数
executor.setMaxPoolSize(20); //最大线程数
executor.setQueueCapacity(1000); //队列大小
executor.setKeepAliveSeconds(300); //线程最大空闲时间
executor.setThreadNamePrefix("fsx-Executor-"); //指定用于新创建的线程名称的前缀。
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
return executor;
}
}
(1)@Async
@Test
public void test3() throws Exception {
System.out.println("main函数开始执行");
myService.longtime();
System.out.println("main函数执行结束");
}
@Async
public void longtime() {
System.out.println("我在执行一项耗时任务");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("完成");
}
(2)AsyncResult
如果需要返回值,耗时方法返回值用AsyncResult包装。
@Test
public void test4() throws Exception {
System.out.println("main函数开始执行");
Future<Integer> future=myService.longtime2();
System.out.println("main函数执行结束");
System.out.println("异步执行结果:"+future.get());
}
@Async
public Future<Integer> longtime2() {
System.out.println("我在执行一项耗时任务");
try {
Thread.sleep(8000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("完成");
return new AsyncResult<>(3);
}