异步编程之美——CompletableFuture

supplyAsync

异步开启一个任务，并返回一个结果；入参为Supply函数式接口；

CompletableFuture busA = CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("A公车发车");SmallTool.sleepMillis(3000);return "A公车到站";
});
SmallTool.printTimeAndThread(busA);

thenCombine

连接两个异步任务，即接收两个异步任务的结果，入参为CompletableStage和BiFunction函数式接口；
也可以等价于在调用了两个CompletableFuture的join()方法后将结果输入到BiFunction；

SmallTool.printTimeAndThread("小白下单烧鸭饭");
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("大厨斩烧鸭！");SmallTool.sleepMillis(3000);return "烧鸭ok";
}).thenCombine(CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("服务员煮米饭");SmallTool.sleepMillis(2000);return "米饭ok";
}), (d, r) -> {SmallTool.printTimeAndThread(d);SmallTool.printTimeAndThread(r);return "服务员盛饭";
});
SmallTool.printTimeAndThread("小白打游戏");
SmallTool.printTimeAndThread(completableFuture.join());
SmallTool.printTimeAndThread("小白吃烧鸭饭");

thenCompose

用于串联两个异步任务，即在前一个任务结束后将其结果作为入参传入Function，Function内部再启动一个CompletableFuture并执行；输入形参是
Function<? super T, ? extends CompletionStage>；

SmallTool.printTimeAndThread("小白到餐厅点餐,点了米饭 + 烧鸭! ");
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("大厨砍烧鸭 ");SmallTool.sleepMillis(3000);return "大厨砍完鸭";
}).thenCompose((res) -> CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread(res);SmallTool.printTimeAndThread("服务员盛饭!");SmallTool.sleepMillis(1000);return "上菜";
}));
SmallTool.printTimeAndThread("小白打游戏");
SmallTool.printTimeAndThread(String.format("%s, 小白吃饭", completableFuture.join()));

applyToEither

用于处理当两个线程都在执行时，不管哪个先执行完，只要有一个返回就触发另一个CompletableStage的执行

CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("A公车发车");SmallTool.sleepMillis(3000);return "A公车到站";
}).applyToEither(CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("B公车发车");SmallTool.sleepMillis(2000);return "B公车到站";}), bus -> bus
).thenCompose(bus -> CompletableFuture.runAsync(() -> {SmallTool.printTimeAndThread(String.format("%s , 小白上车", bus));
})).join();

thenApply

用于将上次的结果作为当前本次操作的输入参数，该方法接收形参是Function<U,V>;有别于thenCompose的Function<U, V extends CompletableStage>;

CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread("项目经历开始讲解需求");SmallTool.sleepMillis(2000);return "讲解完毕";
}).thenApply((preRes) -> {SmallTool.printTimeAndThread(String.format("项目经理 %s, 程序员开始编码", preRes));SmallTool.sleepMillis(3000);return "编码完毕";
}).thenCompose((preRes) -> CompletableFuture.runAsync(() ->{SmallTool.printTimeAndThread(preRes);SmallTool.printTimeAndThread("打包构建");SmallTool.sleepMillis(2000);SmallTool.printTimeAndThread("上测试环境");
})).thenRun(() -> {SmallTool.printTimeAndThread("测试小哥开始测试");SmallTool.sleepMillis(1000);SmallTool.printTimeAndThread("无发现bug");SmallTool.printTimeAndThread("上线");
}).join();

exceptionally

用于获取异步任务的异常结果并进行处理；
入参是Function<Throwable, ? extends T>函数式接口；

CompletableFuture.runAsync(() -> {SmallTool.printTimeAndThread("出bug 出bug 出bug");SmallTool.sleepMillis(3000);throw new RuntimeException("bug");
}).exceptionally((e) -> {e.printStackTrace();return null;
}).join();

handle

不管是正常还是异常结束，当执行完毕时会调用该方法；
入参是BiFunction<? super T, Throwable, ? extends U>，返回一个CompletableFuture;

CompletableFuture<String> join = CompletableFuture.supplyAsync(() -> {SmallTool.sleepMillis(1000);return "avc";
}).handle((res, e) -> {return CompletableFuture.supplyAsync(() -> {SmallTool.printTimeAndThread(res);e.printStackTrace();return "bvc";});
}).join();
System.out.println(join);