refactor: 트랜잭션 매니저 생성 및 TxUserService에서 트랜잭션 중복 로직 제거

app/src/main/java/com/techcourse/service/TransactionCallback.java

@@ -0,0 +1,7 @@
+package com.techcourse.service;
+
+@FunctionalInterface
+public interface TransactionCallback<T> {
+
+    T execute();
+}

app/src/main/java/com/techcourse/service/TransactionManager.java

@@ -0,0 +1,24 @@
+package com.techcourse.service;
+
+import org.springframework.transaction.support.TransactionSynchronizationManager;
+
+import javax.sql.DataSource;
+
+public class TransactionManager {
+
+    private final DataSource dataSource;
+
+    public TransactionManager(final DataSource dataSource) {
+        this.dataSource = dataSource;
+    }
+
+    public <T> T execute(final TransactionCallback<T> callback) {
+        TransactionSynchronizationManager.startNewTransaction(dataSource);
+
+        final T result = callback.execute();
+
+        TransactionSynchronizationManager.finishTransaction(dataSource);
+
+        return result;
+    }
+}

app/src/main/java/com/techcourse/service/TxUserService.java

@@ -1,46 +1,35 @@
 package com.techcourse.service;
 
 import com.techcourse.domain.User;
-import org.springframework.transaction.support.TransactionSynchronizationManager;
-
-import javax.sql.DataSource;
 
 public class TxUserService implements UserService {
 
-    private final DataSource dataSource;
     private final AppUserService userService;
+    private final TransactionManager transactionManager;
 
-    public TxUserService(final DataSource dataSource, final AppUserService userService) {
-        this.dataSource = dataSource;
+    public TxUserService(final AppUserService userService, final TransactionManager transactionManager) {
         this.userService = userService;
+        this.transactionManager = transactionManager;
     }
 
     @Override
     public User findById(final long id) {
-        TransactionSynchronizationManager.startNewTransaction(dataSource);
-
-        final User findUser = userService.findById(id);
-
-        TransactionSynchronizationManager.finishTransaction(dataSource);
-
-        return findUser;
+        return transactionManager.execute(() -> userService.findById(id));
     }
 
     @Override
     public void insert(final User user) {
-        TransactionSynchronizationManager.startNewTransaction(dataSource);
-
-        userService.insert(user);
-
-        TransactionSynchronizationManager.finishTransaction(dataSource);
+        transactionManager.execute(() -> {
+            userService.insert(user);
+            return null;
+        });
     }
 
     @Override
     public void changePassword(final long id, final String newPassword, final String createBy) {
-        TransactionSynchronizationManager.startNewTransaction(dataSource);
-
-        userService.changePassword(id, newPassword, createBy);
-
-        TransactionSynchronizationManager.finishTransaction(dataSource);
+        transactionManager.execute(() -> {
+            userService.changePassword(id, newPassword, createBy);
+            return null;
+        });
     }
 }

app/src/test/java/com/techcourse/service/AppUserServiceTest.java

@@ -51,7 +51,8 @@ void testTransactionRollback() {
         // 애플리케이션 서비스
         final var appUserService = new AppUserService(userDao, userHistoryDao);
         // 트랜잭션 서비스 추상화
-        final var userService = new TxUserService(DataSourceConfig.getInstance(), appUserService);
+        final var transactionManager = new TransactionManager(DataSourceConfig.getInstance());
+        final var userService = new TxUserService(appUserService, transactionManager);
 
         final var newPassword = "newPassword";
         final var createBy = "gugu";