CompletableFuture并发编程实战教程

• runAsync()：执行无返回值的任务
• supplyAsync()：执行有返回值的任务

CompletableFuture run = CompletableFuture.runAsync(() -> {
    System.out.println("执行无返回任务");
});
CompletableFuture supply = CompletableFuture.supplyAsync(() -> {
return "Hello from async";
}, Executors.newFixedThreadPool(2));

• thenApply(Function)：转换结果并返回新值
• thenAccept(Consumer)：消费结果，无返回
• thenRun(Runnable)：不关心结果，只运行后续逻辑

CompletableFuture future = CompletableFuture.supplyAsync(() -> "Hi");
future.thenApply(s -> s + " World")
.thenAccept(System.out::println)
.thenRun(() -> System.out.println("完成"));

• thenCompose：串行组合，前一个任务的结果用于下一个任务（类似 flatMap）
• thenCombine：并行组合，两个任务都完成后合并结果

// 串行：先获取用户，再获取订单
CompletableFuture getUser = CompletableFuture.supplyAsync(() -> new User("Alice"));
CompletableFuture getOrder = getUser.thenCompose(user ->
    CompletableFuture.supplyAsync(() -> new Order(user.getName()))
);
// 并行：同时获取价格和折扣，然后合并
CompletableFuture price = CompletableFuture.supplyAsync(() -> 100.0);
CompletableFuture discount = CompletableFuture.supplyAsync(() -> 0.9);
CompletableFuture finalPrice = price.thenCombine(discount, (p, d) -> p * d);

• exceptionally(Function)：仅处理异常，返回默认值
• handle(BiFunction)：无论是否异常都会执行，可统一处理结果和异常

CompletableFuture broken = CompletableFuture.supplyAsync(() -> {
    throw new RuntimeException("出错了");
});
broken.exceptionally(ex -> "默认值")
.thenAccept(System.out::println);
// 或者用 handle
broken.handle((result, ex) -> {
if (ex != null) {
System.out.println("捕获异常: " + ex.getMessage());
return "恢复结果";
}
return result;
});

• CompletableFuture.allOf(...)：所有任务都完成才算完成，返回 void
• CompletableFuture.anyOf(...)：任意一个完成即完成

CompletableFuture f1 = CompletableFuture.supplyAsync(() -> "A");
CompletableFuture f2 = CompletableFuture.supplyAsync(() -> "B");
CompletableFuture f3 = CompletableFuture.supplyAsync(() -> "C");
CompletableFuture all = CompletableFuture.allOf(f1, f2, f3);
all.thenRun(() -> {
System.out.println("全部完成");
try {
System.out.println(f1.get()); // 获取结果
} catch (Exception e) { }
});