add Cf09 demo:自定义线程池与Async变体

src/main/java/space/anyi/Cf09_CustomExecutor.java

@@ -0,0 +1,42 @@
+package space.anyi;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class Cf09_CustomExecutor {
+    public static void main(String[] args) throws Exception {
+        // 不指定线程池时，默认全部任务都跑在 ForkJoinPool.commonPool 上
+        CompletableFuture<String> defaultOne = CompletableFuture.supplyAsync(() -> {
+            System.out.println("默认线程池: " + Thread.currentThread().getName());
+            return "OK";
+        });
+        defaultOne.join();
+
+        // 重活建议显式指定自定义线程池，避免抢占公共池
+        ExecutorService pool = Executors.newFixedThreadPool(4);
+        CompletableFuture<String> custom = CompletableFuture.supplyAsync(() -> {
+            System.out.println("自定义池 supplyAsync: " + Thread.currentThread().getName());
+            return "结果";
+        }, pool).thenApplyAsync(r -> {
+            System.out.println("自定义池 thenApplyAsync: " + Thread.currentThread().getName());
+            return r + " 加工完成";
+        }, pool);
+        System.out.println("最终结果: " + custom.join());
+        pool.shutdown();
+
+        // 关键区别: 不带 Async 后缀的方法，新任务在哪执行由"触发者"所在的线程决定，
+        // 一般沿用前一个任务的执行线程；带 Async 且不传池子时，提交到 commonPool
+        CompletableFuture<String> noAsync = CompletableFuture.supplyAsync(() -> {
+            System.out.println("supplyAsync        : " + Thread.currentThread().getName());
+            return "r";
+        }).thenApply(r -> {
+            System.out.println("thenApply(无Async) : " + Thread.currentThread().getName());
+            return r;
+        }).thenApplyAsync(r -> {
+            System.out.println("thenApplyAsync(无池): " + Thread.currentThread().getName());
+            return r;
+        });
+        noAsync.join();
+    }
+}