java非同步之CompletableFuture

• 2019 年 10 月 5 日
• 筆記

非同步一般用來處理耗時非常多的計算，如果你的計算量不是很大，調用非同步方法反而沒有執行來的快，我在這裡為大家簡單的整理一下非同步的知識以及用法，我寫了一個Main的類，大家可以跑其中的一個方法，把其他的注釋掉，這樣就可以對非同步有一個大致的了解了。

/**   * main   *   * @author [email protected] |[email protected] |gfu   * @date 2019/8/30   */  public class Main {        public static void main(String[] args) throws InterruptedException {          Async async = new Async();          async.doAsync0();          async.doAsync1();          async.doAsync2();          async.doAsync3();          async.doAsync4();          Thread.sleep(6000);      }  }

import java.util.concurrent.CompletableFuture;  import java.util.concurrent.ExecutionException;    /**   * async   *   * @author [email protected] |[email protected] |gfu   * @date 2019/8/30   */  public class Async {        static final int NINE_MULTI_BY_NINE_LENGTH = 10;        public long print() {          System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + ":");          long start0 = System.nanoTime();          System.out.println("----------start---------");          for (int i = 0; i < NINE_MULTI_BY_NINE_LENGTH; i++) {              for (int j = 0; j < NINE_MULTI_BY_NINE_LENGTH; j++) {                  System.out.print(i * j + " ");              }              System.out.println();          }          long end0 = System.nanoTime();          System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + ":" + (end0 - start0));          return end0 - start0;      }        public void doAsync0() {          CompletableFuture.runAsync(this::print);      }        /**       * need return value       */      public void doAsync1() {          CompletableFuture.supplyAsync(() -> print());      }        /**       * you can see it's method to judge whether must need params or return       * thenAccept can accept pre-stage's result as params       * thenAccept and thenApply must need params       * thenAccept can return void but thenApply need to have a return value       */      public void doAsync2() {          CompletableFuture.supplyAsync(() -> print())                  .thenAccept((i) -> {                      System.out.println("-----------------------------------------------");                      System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + "#" + i);                  });      }        /**       * complete and CompletableFuture's get method can let you get it.s async calculate result       */      public void doAsync3() {          CompletableFuture cf = new CompletableFuture();          cf.complete("hello");          try {              System.out.println(cf.get());          } catch (InterruptedException e) {              e.printStackTrace();          } catch (ExecutionException e) {              e.printStackTrace();          }      }        public void doAsync4() {          CompletableFuture cf0 = CompletableFuture.supplyAsync(() -> print());          CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> "world");          CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> "java8");          CompletableFuture cf = CompletableFuture.allOf(cf0);          try {              System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + ":" + cf0.get());              System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + ":" + cf1.get());              System.out.println(Thread.currentThread().getName() + Thread.currentThread().getId() + ":" + cf2.get());              System.out.println(cf.get());          } catch (InterruptedException e) {              e.printStackTrace();          } catch (ExecutionException e) {              e.printStackTrace();          }      }      }