Java中的异步编程模型：CompletableFuture的使用
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在Java中，异步编程是一种常见的编程范式，用于提高应用程序的响应性和吞吐量。Java 8引入了CompletableFuture类，它是Java中实现异步编程的强大工具之一。CompletableFuture提供了丰富的API，用于编写异步、非阻塞的代码。
CompletableFuture基础
CompletableFuture是一个可以代表异步计算的结果的类。
import cn.juwatech.concurrent.CompletableFuture;
public class CompletableFutureExample {
public static void main(String[] args) {
CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
// 模拟长时间运行的任务
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Hello, CompletableFuture!";
});
future.thenAccept(System.out::println);
}
}组合CompletableFuture
可以组合多个CompletableFuture，以实现复杂的异步逻辑。
public class CombineFutures {
public static void main(String[] args) {
CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> "Hello");
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> "World");
CompletableFuture<String> combined = future1.thenCombine(future2, (s1, s2) -> s1 + " " + s2);
combined.thenAccept(System.out::println);
}
}异常处理
在异步编程中处理异常是非常重要的。
public class ExceptionHandling {
public static void main(String[] args) {
CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
throw new RuntimeException("Error!");
});
future.exceptionally(e -> {
System.out.println("Error: " + e.getMessage());
return "Default value";
}).thenAccept(System.out::println);
}
}等待异步结果
有时需要等待异步操作的结果。
public class WaitForCompletion {
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Done!";
});
String result = future.get(); // 阻塞直到有结果
System.out.println(result);
}
}使用CompletableFuture进行并行处理
可以并行执行多个任务，并合并它们的结果。
public class ParallelProcessing {
public static void main(String[] args) {
CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> expensiveOperation(1));
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> expensiveOperation(2));
CompletableFuture<Void> combinedFuture = CompletableFuture.allOf(future1, future2);
combinedFuture.thenRun(() -> {
System.out.println("Both tasks are completed");
});
}
private static String expensiveOperation(int number) {
// 模拟长时间运行的任务
try {
Thread.sleep(1000 * number);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Result of " + number;
}
}CompletableFuture与Stream API结合
CompletableFuture可以与Java 8的Stream API结合使用。
import java.util.stream.Stream;
import cn.juwatech.concurrent.CompletableFuture;
public class CompletableFutureWithStream {
public static void main(String[] args) {
Stream.of("Task1", "Task2", "Task3")
.map(task -> CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return task + " completed";
}))
.map(CompletableFuture::join)
.forEach(System.out::println);
}
}定制线程池
可以为CompletableFuture定制线程池。
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import cn.juwatech.concurrent.CompletableFuture;
public class CustomThreadPool {
private static final ExecutorService executor = Executors.newFixedThreadPool(4);
public static void main(String[] args) {
CompletableFuture<Void> future = CompletableFuture.supplyAsync(() -> "Hello", executor)
.thenApplyAsync(s -> s + " World", executor)
.thenAcceptAsync(System.out::println, executor);
future.join();
executor.shutdown();
}
}总结
CompletableFuture是Java中强大的异步编程工具，它提供了丰富的API来实现复杂的异步逻辑。通过使用CompletableFuture，可以编写出更高效、更响应灵敏的Java应用程序。无论是组合多个异步任务、处理异常、等待异步结果，还是与Stream API结合使用，CompletableFuture都是一个强大的工具。
