日常開發(fā)中可能會遇到批量發(fā)起請求的場景怠褐，如：從某個服務(wù)器拉取大批量數(shù)據(jù)，如果一次拉取您宪，數(shù)據(jù)量太大奈懒。采用分頁拉取方式，一頁一頁拉取宪巨，比較耗時磷杏，此時我們可以批量的同時去拉數(shù)據(jù)。
如何發(fā)起批量請求呢捏卓？可以使用Java多線程去實(shí)現(xiàn)极祸。每個線程拉取數(shù)據(jù)的執(zhí)行時間可能不一致，我們希望先執(zhí)行完任務(wù)的線程可以優(yōu)先返回?cái)?shù)據(jù)怠晴，不是等待所有線程都執(zhí)行完遥金，才返回?cái)?shù)據(jù)。
Future方式
public static void sleep(long time) {
try {
TimeUnit.SECONDS.sleep(time);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void test() {
long start = System.currentTimeMillis();
//定義ExecutorService
ExecutorService executor = Executors.newFixedThreadPool(3);
//定義批量任務(wù)蒜田，每個任務(wù)的耗時不等
final List<Callable<Integer>> tasks = Arrays.asList(
() -> {
sleep(30L);
System.out.println("Task 30 completed done.");
return 30;
},
() -> {
sleep(10L);
System.out.println("Task 10 completed done.");
return 10;
},
() -> {
sleep(20L);
System.out.println("Task 20 completed done.");
return 20;
}
);
//批量提交執(zhí)行異步任務(wù)稿械，
try {
List<Future<Integer>> futures = executor.invokeAll(tasks);
futures.forEach(future -> {
try {
System.out.println("返回結(jié)果： " + future.get());
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
});
executor.shutdown();
} catch (InterruptedException e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
long seed = end - start;
System.out.format("seed=%s", seed);
}
執(zhí)行結(jié)果：
Task 30 completed done.
Task 10 completed done.
Task 20 completed done.
返回結(jié)果： 30
返回結(jié)果： 10
返回結(jié)果： 20
seed=30068
我們無法優(yōu)先獲取最先執(zhí)行完任務(wù)線程的結(jié)果，而是等到耗時(30s)最長的任務(wù)執(zhí)行完畢后才可以拿到結(jié)果物邑。
CompletableFuture方式
public static void test2() {
long start = System.currentTimeMillis();
List<String> list = Arrays.asList("1", "2", "3");
List<CompletableFuture<String>> futures = list.stream()
.map(item ->
CompletableFuture.supplyAsync(() -> {
if ("1".equals(item)) {
sleep(10L);
} else if ("2".equals(item)) {
sleep(30L);
} else {
sleep(20L);
}
System.out.println("thread name: " + Thread.currentThread().getName() + " task: " + item);
return "任務(wù)" + item;
}
)).collect(Collectors.toList());
futures.forEach(future -> {
future.thenAccept(result -> {
System.out.println("返回結(jié)果： " + result);
});
});
futures.forEach(future -> {
future.join();
});
long end = System.currentTimeMillis();
long seed = end - start;
System.out.format("seed=%s", seed);
}
執(zhí)行結(jié)果：
thread name: ForkJoinPool.commonPool-worker-9 task: 1
返回結(jié)果： 任務(wù)1
thread name: ForkJoinPool.commonPool-worker-11 task: 3
返回結(jié)果： 任務(wù)3
thread name: ForkJoinPool.commonPool-worker-2 task: 2
返回結(jié)果： 任務(wù)2
seed=30079
可以優(yōu)先拿到最先執(zhí)行完任務(wù)線程的執(zhí)行結(jié)果溜哮。
CompletionService方式
public static void test3() {
long start = System.currentTimeMillis();
//定義ExecutorService
ExecutorService executor = Executors.newFixedThreadPool(3);
//定義批量任務(wù)，每個任務(wù)的耗時不等
final List<Callable<Integer>> tasks = Arrays.asList(
() -> {
sleep(30L);
System.out.println("Task 30 completed done.");
return 30;
},
() -> {
sleep(10L);
System.out.println("Task 10 completed done.");
return 10;
},
() -> {
sleep(20L);
System.out.println("Task 20 completed done.");
return 20;
}
);
//批量提交執(zhí)行異步任務(wù)色解，
try {
CompletionService<Integer> completionService = new ExecutorCompletionService<>(executor);
tasks.forEach(completionService::submit);
for (int i = 0; i < tasks.size(); i++) {
try {
System.out.println("返回結(jié)果： " + completionService.take().get());
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
executor.shutdown();
} catch (Exception e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
long seed = end - start;
System.out.format("seed=%s", seed);
}
執(zhí)行結(jié)果：
Task 10 completed done.
返回結(jié)果： 10
Task 20 completed done.
Task 30 completed done.
返回結(jié)果： 20
返回結(jié)果： 30
seed=30064
可以優(yōu)先拿到最先執(zhí)行完任務(wù)線程的執(zhí)行結(jié)果茂嗓。
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