Future 和 CompletableFuture 异步任务 in Java

Future 异步任务

定义Callable接口的实现

import java.util.concurrent.Callable;

public class RealDataCallable implements Callable<String> {
    
    private String para;
    public RealDataCallable(String para) {
    this.para = para;
    }

    @Override
    public String call() throws Exception {
    StringBuffer sb = new StringBuffer();
    for(int i=0; i<10; i++) {
        sb.append(para);
        Thread.sleep(1000);
    }
    return sb.toString();
    }

}

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;

public class FutureDemo {

    public static void main(String[] args) throws InterruptedException, ExecutionException {

    FutureTask<String> future = new FutureTask<String>(new RealDataCallable("a"));
    
    ExecutorService es = Executors.newFixedThreadPool(1);
    //Future 是异步任务，提交请求之后，这里必然是立即返回的，因为程序不会阻塞
    //接下来，不用关心数据是如何产生的。
    //可以去做一些额外的事情，然后在需要的时候可以通过Future.get()得到实际的数据
    es.submit(future);
    System.out.println("请求完毕");

    //使用 sleep 代替其他业务逻辑的处理
    Thread.sleep(1000);
    //获得call()方法的返回值，如果此时call()方法没有执行完成，则会等待
    System.out.println("数据： " + future.get());
    }

}

通过CompletableFuture 提供的进一步封装，可以很容易实现Future模式那样的异步调用。

实例如下：

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class AsyncTaskUseCompletableFuture {

    
    public static void main(String[] args) throws InterruptedException, ExecutionException {
    
    final CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> calc(50));
    
    System.out.println(future.get());

    }
    public static Integer calc(Integer para) {
    try {
        //模拟一个长时间的执行
        Thread.sleep(1000);
    } catch (InterruptedException e) {
    }
    
    return para * para;
    }

}

CompletableFuture 的组合

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class ComposeCompletableFuture {

    public static void main(String[] args) throws InterruptedException, ExecutionException {

    //thenCompose 组合CompletableFuture
//    CompletableFuture<Void> fu = CompletableFuture.supplyAsync(() -> calc(50))
//        .thenCompose((i) -> CompletableFuture.supplyAsync(() -> calc(i)))
//        .thenApply((str) -> """ + str + """ )
//        .thenAccept(System.out::println);
    
    //thenCombine 组合CompletableFuture
    CompletableFuture<Integer> intFuture = CompletableFuture.supplyAsync(() -> calc(50));
    CompletableFuture<Integer> intFuture2 = CompletableFuture.supplyAsync(() -> calc(25));    
 
    CompletableFuture<Integer> fu = intFuture.thenCombine(intFuture2, (i,j) -> (i + j));
    
    System.out.println(fu.get());
    
    }

    public static Integer calc(Integer para) {
    return para / 2;
    }
}