java之使用CompletableFuture入门1

Java 17

简介

JDK中异步执行任务。

源码：

// A Future that may be explicitly completed (setting its value and status), 
// and may be used as a CompletionStage, supporting dependent functions 
// and actions that trigger upon its completion.
public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
    // ...
}

//
// 实现的2个接口

// A Future represents the result of an asynchronous computation.
public interface Future<V> {
    // ...
}

// A stage of a possibly asynchronous computation, 
// that performs an action or computes a value when another CompletionStage completes. 
public interface CompletionStage<T> {
    // ...
}

supplyAsync

注，这个自己用的比较多。

有返回值的任务。

supplyAsync 源码：

下文使用第一个。第二个可以自定义线程池。

代码：

private static void testCompletableFuture1() {
    log.info("in testCompletableFuture");

    StopWatch sw = new StopWatch();

    sw.start();
    CompletableFuture<LocalDateTime> task = CompletableFuture.supplyAsync(()->{
        log.info("in CompletableFuture task");
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        return LocalDateTime.now();
    });
    sw.stop();

    try {
        log.info("等待结果...");
        sw.start();
        LocalDateTime ldt = task.get();
        sw.stop();
        log.info("结果={}", ldt);
    } catch (InterruptedException e) {
        throw new RuntimeException(e);
    } catch (ExecutionException e) {
        throw new RuntimeException(e);
    } finally {
        log.info("耗时：{}毫秒，sw=\n{}", sw.getTotalTimeMillis(), sw.prettyPrint());
    }
}

结果：

17:25:37.697 [main] INFO com.example.test.TestMain -- in testCompletableFuture
17:25:37.706 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- in CompletableFuture task
17:25:37.706 [main] INFO com.example.test.TestMain -- 等待结果...
17:25:41.714 [main] INFO com.example.test.TestMain -- 结果=2024-09-28T17:25:41.713449200
17:25:41.749 [main] INFO com.example.test.TestMain -- 耗时：4010毫秒，sw=
StopWatch '': running time = 4010560200 ns
---------------------------------------------
ns % Task name
---------------------------------------------
003454300 000%
4007105900 100%

get：

ForkJoinPool.commonPool-worker-1，线程名，使用了一个 ForkJoinPool。

造异常

结果：task.get() 调用时排除异常，没有输出结果。

17:27:45.155 [main] INFO com.example.test.TestMain -- in testCompletableFuture

17:27:45.163 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- in CompletableFuture task

17:27:45.163 [main] INFO com.example.test.TestMain -- 等待结果...

17:27:45.184 [main] INFO com.example.test.TestMain -- 耗时：3毫秒，sw=

StopWatch '': running time = 3313300 ns

---------------------------------------------

ns % Task name

---------------------------------------------

003313300 100%

Exception in thread "main" java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: 造异常

at com.example.test.TestMain.testCompletableFuture1(TestMain.java:81)

at com.example.test.TestMain.main(TestMain.java:45)

Caused by: java.util.concurrent.ExecutionException: java.lang.RuntimeException: 造异常

at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)

at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)

at com.example.test.TestMain.testCompletableFuture1(TestMain.java:75)

... 1 more

Caused by: java.lang.RuntimeException: 造异常

at com.example.test.TestMain.lambda$testCompletableFuture1$0(TestMain.java:60)

at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1768)

at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1760)

at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)

at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)

at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)

at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)

at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

使用 exceptionally 处理异常

新增代码：

结果：task.get() 正常执行，没有抛出异常。

17:34:02.625 [main] INFO com.example.test.TestMain -- in testCompletableFuture

17:34:02.639 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- in CompletableFuture task

17:34:02.640 [main] ERROR com.example.test.TestMain -- task 发生异常：e=

java.util.concurrent.CompletionException: java.lang.RuntimeException: 造异常

at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315)

at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320)

at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1770)

at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1760)

at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)

at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)

at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)

at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)

at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

Caused by: java.lang.RuntimeException: 造异常

at com.example.test.TestMain.lambda$testCompletableFuture1$0(TestMain.java:60)

at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1768)

... 6 common frames omitted

17:34:02.646 [main] INFO com.example.test.TestMain -- 等待结果...

17:34:02.647 [main] INFO com.example.test.TestMain -- 结果=1970-01-01T00:00

17:34:02.682 [main] INFO com.example.test.TestMain -- 耗时：14毫秒，sw=

StopWatch '': running time = 14376300 ns

---------------------------------------------

ns % Task name

---------------------------------------------

014364800 100%

000011500 000%

注，这里时造了一个RuntimeException 异常，可以进一步造一个 InterruptedException 试试（TODO）。

构造器创建

通过构造函数创建 CompletableFuture 对象：

CompletableFuture<String> task = new CompletableFuture<>();

代码：

private static void testCompletableFuture0() {
    CompletableFuture<String> task = new CompletableFuture<>();
    log.info("task={}, {}, {}", task.isCancelled(), task.isDone(), task.isCompletedExceptionally());

    Thread nt = new Thread(() ->{
        log.info("Thread nt 1");
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        log.info("Thread nt 2");

        task.complete("nt done.");
    });
    nt.start();

    try {
        log.info("task.get()={}", task.get());
        log.info("task.isx3={}, {}, {}", task.isCancelled(), task.isDone(), task.isCompletedExceptionally());
    } catch (InterruptedException e) {
        throw new RuntimeException(e);
    } catch (ExecutionException e) {
        throw new RuntimeException(e);
    }

    log.info("end");
}

结果：

19:36:26.363 [main] INFO com.example.test.TestMain -- task=false, false, false
19:36:26.369 [Thread-0] INFO com.example.test.TestMain -- Thread nt 1
19:36:30.381 [Thread-0] INFO com.example.test.TestMain -- Thread nt 2
19:36:30.382 [main] INFO com.example.test.TestMain -- task.get()=nt done.
19:36:30.382 [main] INFO com.example.test.TestMain -- task.isx3=false, true, false
19:36:30.382 [main] INFO com.example.test.TestMain -- end

死锁

注释掉上面的 “// task.complete("nt done.");”，此时，程序无法停止。

结果：

task.get() 一直卡住了。

19:38:49.402 [main] INFO com.example.test.TestMain -- task=false, false, false
19:38:49.412 [Thread-0] INFO com.example.test.TestMain -- Thread nt 1
19:38:53.419 [Thread-0] INFO com.example.test.TestMain -- Thread nt 2

runAsync

没有返回值。

runAsync 源码：

代码：

// 调用：
// testCompletableFuture2(1); // 无异常
// testCompletableFuture2(2); // 造异常

private static void testCompletableFuture2(int ctl) {
    log.info("ctl={}", ctl);

    // 形参为 Void
    CompletableFuture<Void> task = CompletableFuture.runAsync(()->{
        log.info("task 1");

        if (ctl % 2 == 0) {
            throw new RuntimeException("异常ctl=" + ctl);
        }

        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException e) {
            log.error("task ex");
            throw new RuntimeException(e);
        }
        log.info("task 3");
    });
    //                .exceptionally(ex->{ // 处理异常
    //            log.error("exceptionally 处理异常：ex=", ex);
    //            return null;
    //        });

    try {
        log.info("2");
        var x = task.get();
        log.info("3.x={}", x);
    } catch (InterruptedException e) {
        throw new RuntimeException(e);
    } catch (ExecutionException e) {
        throw new RuntimeException(e);
    } finally {
        log.info("4.task.isx3={}, {}, {}", task.isCancelled(), task.isDone(), task.isCompletedExceptionally());
    }

    log.info("end");
}

结果：

20:03:37.633 [main] INFO com.example.test.TestMain -- ctl=1

20:03:37.646 [main] INFO com.example.test.TestMain -- 2

20:03:37.646 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- task 1

20:03:41.655 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- task 3

20:03:41.656 [main] INFO com.example.test.TestMain -- 3.x=null

20:03:41.657 [main] INFO com.example.test.TestMain -- 4.task.isx3=false, true, false

20:03:41.658 [main] INFO com.example.test.TestMain -- end

20:03:41.658 [main] INFO com.example.test.TestMain -- ctl=2

20:03:41.658 [main] INFO com.example.test.TestMain -- 2

20:03:41.658 [ForkJoinPool.commonPool-worker-1] INFO com.example.test.TestMain -- task 1

20:03:41.675 [main] INFO com.example.test.TestMain -- 4.task.isx3=false, true, true

Exception in thread "main" java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: 异常ctl=2

at com.example.test.TestMain.testCompletableFuture2(TestMain.java:85)

at com.example.test.TestMain.main(TestMain.java:50)

Caused by: java.util.concurrent.ExecutionException: java.lang.RuntimeException: 异常ctl=2

at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)

at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)

at com.example.test.TestMain.testCompletableFuture2(TestMain.java:80)

... 1 more

Caused by: java.lang.RuntimeException: 异常ctl=2

at com.example.test.TestMain.lambda$testCompletableFuture2$0(TestMain.java:62)

at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)

at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)

at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)

at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)

at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)

at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)

at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

使用 exceptionally 处理异常

和前面一样，不过，返回值为 return null。

修改的代码：

结果：

20:08:59.546 [main] INFO com.benzl.tl.back.api.TestMain -- ctl=1

20:08:59.558 [ForkJoinPool.commonPool-worker-1] INFO com.benzl.tl.back.api.TestMain -- task 1

20:08:59.558 [main] INFO com.benzl.tl.back.api.TestMain -- 2

20:09:03.563 [ForkJoinPool.commonPool-worker-1] INFO com.benzl.tl.back.api.TestMain -- task 3

20:09:03.565 [main] INFO com.benzl.tl.back.api.TestMain -- 3.x=null

20:09:03.565 [main] INFO com.benzl.tl.back.api.TestMain -- 4.task.isx3=false, true, false

20:09:03.565 [main] INFO com.benzl.tl.back.api.TestMain -- end

20:09:03.565 [main] INFO com.benzl.tl.back.api.TestMain -- ctl=2

20:09:03.566 [main] INFO com.benzl.tl.back.api.TestMain -- 2

20:09:03.566 [ForkJoinPool.commonPool-worker-1] INFO com.benzl.tl.back.api.TestMain -- task 1

20:09:03.580 [ForkJoinPool.commonPool-worker-1] ERROR com.benzl.tl.back.api.TestMain -- exceptionally 处理异常：ex=

java.util.concurrent.CompletionException: java.lang.RuntimeException: 异常ctl=2

at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315)

at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320)

at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1807)

at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)

at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)

at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)

at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)

at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)

at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

Caused by: java.lang.RuntimeException: 异常ctl=2

at com.benzl.tl.back.api.TestMain.lambda$testCompletableFuture2$0(TestMain.java:62)

at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)

... 6 common frames omitted

20:09:03.596 [main] INFO com.benzl.tl.back.api.TestMain -- 3.x=null

20:09:03.597 [main] INFO com.benzl.tl.back.api.TestMain -- 4.task.isx3=false, true, false

20:09:03.597 [main] INFO com.benzl.tl.back.api.TestMain -- end

Process finished with exit code 0

注意，“4.task.isx3=false, true, false”，只有中间一个 true 了。

---end---

或许还要写更多内容，更高级点的，比如，线程池、多个CompletableFuture对象配合使用等……

参考资料

1、通俗易懂讲 CompletableFuture

https://www.cnblogs.com/cyrus-s/p/15485182.html

posted @ 2021-10-30 15:49 三木同学

2、1.java多线程之FutureTask、Future、CompletableFuture
2024-04-09
https://developer.aliyun.com/article/1478152
作者：程序三两行

3、

ben发布于博客园

posted @ 2024-09-28 20:20 快乐的欧阳天美1114 阅读(7) 评论(0) 编辑收藏举报

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java之使用CompletableFuture入门1

简介

supplyAsync

造异常

使用 exceptionally 处理异常

构造器创建

死锁

runAsync

使用 exceptionally 处理异常

参考资料

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