Java StreamAPI 和 Reactive Programming
一、Lambad
@FunctionalInterface interface Calculator { int add(int a, int b); default int add(long a, int b) { return (int) a + b; } } public static void main(String[] args) { Calculator calculator = new Calculator() { @Override public int add(int a, int b) { return a + b; } }; calculator = (a, b) -> { return a + b; }; calculator = (a, b) -> a + b; calculator = Integer::sum; new Thread(() -> System.out.println("runnable")).start(); }
二、Function
java.util.function：https://blog.csdn.net/CKXGZXA/article/details/124227749
https://ruanyifeng.com/blog/2017/02/fp-tutorial.html
https://github.com/ruanyf/es6tutorial/blob/gh-pages/docs/fp.md
https://ruanyifeng.com/blog/2017/03/pointfree.html
https://ruanyifeng.com/blog/2015/04/tail-call.html
https://github.com/shfshanyue/fp-jargon-zh
// 功能函数：有入参，有出参 Function<String, Integer> function = x -> Integer.parseInt(x); function = Integer::parseInt; System.out.println(function.apply("function")); // 消费者：有入参，无出参 Consumer<String> consumer = a -> System.out.println(a); consumer = System.out::println; consumer.accept("consumer"); // 提供者：无入参，有出参 Supplier<String> supplier = () -> "supplier"; System.out.println(supplier.get()); // 普通函数：无入参，无出参 Runnable runnable = () -> System.out.println("runnable"); new Thread(runnable).start(); // 消费者：有两个(bi)入参，无出参 BiConsumer<String, String> biConsumer = (a, b) -> System.out.println(a + b); biConsumer.accept("biweekly", "consumer"); // 断言 Predicate<String> predicate = x -> "predicate".equals(x); predicate = "predicate"::equals; System.out.println(predicate.test("predicate")); System.out.println(predicate.negate().test("predicate"));
sample
public static void main(String[] args) { Supplier<String> supplier = () -> "1"; // 提供者 Predicate<String> predicate = x -> x.matches("[0-9]+"); // 断言 Function<String, Integer> function = Integer::parseInt; // 功能函数 Consumer<Integer> consumer = x -> { // 消费者 if ((x & 1) == 1) System.out.println("odd number " + x); else System.out.println("even number " + x); }; if (predicate.test(supplier.get())) { // 使用 consumer.accept(function.apply(supplier.get())); } else { System.out.println("not number"); } methon( () -> "1", x -> x.matches("[0-9]+"), Integer::parseInt, System.out::println ); } static void methon(Supplier<String> supplier, Predicate<String> predicate, Function<String, Integer> function, Consumer<Integer> consumer) { if (predicate.test(supplier.get())) { consumer.accept(function.apply(supplier.get())); } else { System.out.println("not number"); } }
三、StreamAPI
数据流 -> N个中间操作 -> 一个终止操作：https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html
Stream<Integer> stream = Stream.of(1, 2, 3); stream = Stream.concat(stream, Stream.of(4, 5, 6)); Stream<Object> objectStream = Stream.builder().add(1).add(2).add(3).build(); Stream<Object> emptyStream = Stream.empty(); Stream<Integer> intStream = IntStream.rangeClosed(0, 9).boxed(); Stream<String> arrayStream = Arrays.stream(new String[]{"a", "b", "c"}); Stream.generate(Math::random).limit(10).forEach(System.out::println); // 无限流 Stream.iterate(0, t -> t + 2).limit(10).forEach(System.out::println); stream = stream.parallel(); // 并发 // stream = StreamSupport.stream(Spliterators.spliterator(), true); // 自定义线程池
四、Reactive Stream
Flow：https://www.reactive-streams.org & https://reactivemanifesto.org/zh-CN
public static void main(String[] args) throws InterruptedException { // 发布者 // Flow.Publisher<String> publisher = new Flow.Publisher<>() { // Flow.Subscriber<? super String> subscriber; // @Override // public void subscribe(Flow.Subscriber<? super String> subscriber) { // this.subscriber = subscriber; // } // }; SubmissionPublisher<String> publisher = new SubmissionPublisher<>(); // 中间处理器 class Processor extends SubmissionPublisher<String> implements Flow.Processor<String, String> { Flow.Subscription subscription; @Override public void onSubscribe(Flow.Subscription subscription) { this.subscription = subscription; subscription.request(1); } @Override public void onNext(String item) { submit(item + "p"); subscription.request(1); } @Override public void onError(Throwable throwable) { getSubscribers().parallelStream().forEach(x -> x.onError(throwable)); } @Override public void onComplete() { getSubscribers().parallelStream().forEach(Flow.Subscriber::onComplete); } } Flow.Processor<String, String> processor = new Processor(); // 订阅者 Flow.Subscriber<String> subscriber = new Flow.Subscriber<>() { Flow.Subscription subscription; // 订阅关系 @Override public void onSubscribe(Flow.Subscription subscription) { System.out.println("订阅开始"); this.subscription = subscription; // subscription.request(1); // 从上游请求一个数据 subscription.request(Long.MAX_VALUE); // 从上游请求数据 } @Override public void onNext(String item) { System.out.println("订阅者接收到数据：" + item); // subscription.request(1); // 从上游请求一个数据 } @Override public void onError(Throwable throwable) { System.out.println("订阅者接收到错误信息：" + throwable); // subscription.cancel(); // 取消订阅 } @Override public void onComplete() { System.out.println("订阅者接收到完成信号"); } }; // 绑定发布者和订阅者 // publisher.subscribe(subscriber); // 发布者绑定处理器，处理器绑定订阅者 publisher.subscribe(processor); processor.subscribe(subscriber); for (int i = 0; i < 10; i++) { // 发布数据 publisher.submit(String.valueOf(i)); } publisher.closeExceptionally(new RuntimeException("发布错误")); publisher.close(); // 完成发布 Thread.sleep(99999); Flow.Subscription subscription = new Flow.Subscription() { @Override public void request(long n) { } @Override public void cancel() { } }; }
五、Reactor
高并发：缓存、异步、队排好。高可用：分片、复制、选领导
