diff --git a/DailyImportGate.java b/DailyImportGate.java
new file mode 100644
--- /dev/null
+++ b/DailyImportGate.java
@@ -0,0 +1,27 @@
+package com.ithome.day09.review;
+
+import java.util.Locale;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class DailyImportGate {
+
+    private final Set<String> runningWorkspaces =
+            ConcurrentHashMap.newKeySet();
+
+    public boolean tryStart(String workspaceId) {
+        if (workspaceId.isBlank()) {
+            throw new IllegalArgumentException("workspaceId must not be blank");
+        }
+        String key = workspaceId.strip().toLowerCase(Locale.ROOT);
+        if (runningWorkspaces.contains(key)) {
+            return false;
+        }
+        runningWorkspaces.add(key);
+        return true;
+    }
+
+    public void finish(String workspaceId) {
+        runningWorkspaces.remove(workspaceId);
+    }
+}