✨ Feat : Database

src/main/java/com/thread/concurrency/db/Account.java

@@ -0,0 +1,4 @@
+package com.thread.concurrency.db;
+
+public record Account(long balance, long updateMilli, long updateNano) {
+}

src/main/java/com/thread/concurrency/db/BalanceController.java

@@ -0,0 +1,9 @@
+package com.thread.concurrency.db;
+
+public interface BalanceController {
+    Account balance(long id);
+
+    Account deposit(long id, long amount);
+
+    Account withdraw(long id, long amount);
+}

src/main/java/com/thread/concurrency/db/Database.java

@@ -0,0 +1,9 @@
+package com.thread.concurrency.db;
+
+public interface Database {
+    // deposit balance: 일급 함수 스타일
+    Account balance(long id, long balance);
+
+    // initial balance
+    Account balance(long id);
+}

src/main/java/com/thread/concurrency/db/SimpleDatabase.java

@@ -0,0 +1,32 @@
+package com.thread.concurrency.db;
+
+
+import org.springframework.stereotype.Component;
+
+import java.util.HashMap;
+
+import static java.lang.Math.random;
+
+@Component
+public final class SimpleDatabase {
+    private final HashMap<Long, Account> db = new HashMap<>();
+
+    Account balance(long id, long balance) {
+        try {
+            Thread.sleep((long) (random() * 300L + 100));
+        } catch (InterruptedException ignored) {
+        }
+        var account = new Account(balance, System.currentTimeMillis(), System.nanoTime());
+        db.put(id, account);
+        return account;
+    }
+
+    Account balance(long id) {
+        try {
+            Thread.sleep((long) (random() * 300L + 100));
+        } catch (InterruptedException ignored) {
+        }
+        var account = db.get(id);
+        return account != null ? account : new Account(0, System.currentTimeMillis(), System.nanoTime());
+    }
+}