java 中的 CompletableFuture

CompletableFuture 是 Java 8 引入的新类，提供了更强大和灵活的异步编程能力。CompletableFuture 可以让你更轻松地创建、组合和管理异步任务。下面是一些基本用法和示例。

基本用法

1. 创建一个异步任务

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
            try {
                // 模拟长时间的任务
                Thread.sleep(2000);
                System.out.println("任务完成!");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });

        // 等待任务完成
        future.join();
    }
}

2. 返回结果的异步任务

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {
            try {
                // 模拟长时间的任务
                Thread.sleep(2000);
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        });

        // 获取结果
        Integer result = future.join();
        System.out.println("计算结果: " + result);
    }
}

链式调用

1. thenApply：用于对结果进行转换

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        });

        CompletableFuture<String> future2 = future.thenApply(result -> "结果: " + result);

        // 获取转换后的结果
        String result = future2.join();
        System.out.println(result);
    }
}

2. thenAccept：用于消费结果

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        });

        future.thenAccept(result -> System.out.println("计算结果: " + result));

        // 等待任务完成
        future.join();
    }
}

3. thenCombine：用于组合两个 CompletableFuture

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future1 = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        });

        CompletableFuture<Integer> future2 = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(3000);
                return 456;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        });

        CompletableFuture<Integer> combinedFuture = future1.thenCombine(future2, (result1, result2) -> result1 + result2);

        // 获取组合后的结果
        Integer result = combinedFuture.join();
        System.out.println("组合结果: " + result);
    }
}

异常处理

1. exceptionally：用于处理异常

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
                if (true) {
                    throw new RuntimeException("计算错误!");
                }
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        }).exceptionally(ex -> {
            System.out.println("异常: " + ex.getMessage());
            return -1;
        });

        // 获取结果
        Integer result = future.join();
        System.out.println("计算结果: " + result);
    }
}

2. handle：用于处理结果或异常

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(2000);
                if (true) {
                    throw new RuntimeException("计算错误!");
                }
                return 123;
            } catch (InterruptedException e) {
                e.printStackTrace();
                return null;
            }
        }).handle((result, ex) -> {
            if (ex != null) {
                System.out.println("异常: " + ex.getMessage());
                return -1;
            }
            return result;
        });

        // 获取结果
        Integer result = future.join();
        System.out.println("计算结果: " + result);
    }
}

通过以上示例，你可以看到 CompletableFuture 提供了丰富的功能来处理异步任务，并且可以方便地进行任务组合和异常处理。