Create E20250811 Future, Reactive 연습.md

Author: ecsimsw

backend/E20250811 Future, Reactive 연습.md

@@ -0,0 +1,45 @@
+``` java
+public void asIs() {
+    var deviceIds = new ArrayList<String>();
+    var windowSize = 5;
+    var hasNextCount = windowSize;
+    var page = 0;
+    while(hasNextCount == windowSize) {
+        var futures = new ArrayList<CompletableFuture<PlatformUserDevicesResponse>>();
+        for (var i = 1; i <= windowSize; i++) {
+            var pageNumber = windowSize * page + i;
+            futures.add(getDeviceListWithPage(pageNumber));
+        }
+        var deviceResponses = futures.stream()
+            .map(CompletableFuture::join)
+            .toList();
+        hasNextCount = (int) deviceResponses.stream()
+            .filter(res -> res.hasNext)
+            .count();
+        deviceResponses.stream()
+            .filter(res -> !res.isEmpty())
+            .map(res -> res.deviceId)
+            .forEach(deviceIds::add);
+        page++;
+    }
+    System.out.println(deviceIds);
+}
+
+private final AtomicInteger index = new AtomicInteger(1);
+
+@SneakyThrows
+private CompletableFuture<PlatformUserDevicesResponse> getDeviceListWithPage(int page) {
+    log.info("Api call page : {} {}", page, System.currentTimeMillis());
+    var i = index.getAndIncrement();
+    if(i > 14) {
+        return CompletableFuture.supplyAsync(() -> {
+            sleep(1000);
+            return new PlatformUserDevicesResponse(false, null);
+        });
+    }
+    return CompletableFuture.supplyAsync(() -> {
+        sleep(1000);
+        return new PlatformUserDevicesResponse(true, i+ "");
+    });
+}
+```