Fix concurrency transactional

pom.xml

@@ -61,6 +61,16 @@
 			<version>1.18.3</version>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.retry</groupId>
+			<artifactId>spring-retry</artifactId>
+			<version>2.0.3</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-aspects</artifactId>
+			<version>6.0.11</version>
+		</dependency>
 	</dependencies>
 
 	<build>

src/main/java/com/bifurcated/wallet/service/WalletService.java

@@ -5,9 +5,14 @@
 import com.bifurcated.wallet.errors.NotEnoughMoneyError;
 import com.bifurcated.wallet.errors.WalletNotFoundError;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.retry.annotation.Backoff;
+import org.springframework.retry.annotation.Retryable;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Isolation;
+import org.springframework.transaction.annotation.Propagation;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.sql.SQLException;
 import java.util.UUID;
 
 
@@ -20,11 +25,15 @@ public WalletService(WalletRepo walletRepo) {
         this.walletRepo = walletRepo;
     }
 
-    @Transactional
+    @Transactional(
+            isolation = Isolation.SERIALIZABLE,
+            propagation = Propagation.REQUIRES_NEW)
+    @Retryable(retryFor = SQLException.class, maxAttempts = 17, backoff = @Backoff(delay = 500))
     public Wallet addAmount(UUID id, Float amount) {
         var wallet = walletRepo.findById(id).orElseThrow(WalletNotFoundError::new);
         wallet.setAmount(wallet.getAmount() + amount);
-        return walletRepo.save(wallet);
+        Wallet save = walletRepo.save(wallet);
+        return save;
     }
 
     @Transactional

src/test/java/com/bifurcated/wallet/controller/WalletControllerTest.java

@@ -6,14 +6,23 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.MediaType;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.ResultActions;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
 
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
@@ -26,6 +35,7 @@
 @AutoConfigureMockMvc
 @ActiveProfiles("test")
 class WalletControllerTest {
+    private static Logger logger = LoggerFactory.getLogger(WalletControllerTest.class);
     private static final String END_POINT_PATH = "/api/v1";
     @Autowired
     private MockMvc mockMvc;
@@ -34,7 +44,6 @@ class WalletControllerTest {
     @Autowired
     private WalletRepo repository;
 
-
     @BeforeEach
     public void setup() {
         repository.deleteAll();
@@ -155,4 +164,39 @@ public void testWalletGetAmountNotFound() throws Exception {
                 .andDo(print())
                 .andExpect(status().isNotFound());
     }
+
+    @Test
+    public void testWalletDepositDDOSAttack() throws Exception {
+        record WalletRequest(UUID valletId, String operationType, Float amount){}
+        record BalanceResponse(Float amount){}
+        UUID id = UUID.fromString("b3919077-79e6-4570-bfe0-980ef18f3731");
+        WalletRequest walletRequest = new WalletRequest(
+                id, "DEPOSIT", 1000F);
+
+        String requestBody = objectMapper.writeValueAsString(walletRequest);
+
+        ExecutorService executorService = Executors.newFixedThreadPool(10000);
+        List<Future<ResultActions>> futures = new ArrayList<>();
+        for (int i = 0; i < 300; i++) {
+            Callable<ResultActions> callable = () -> {
+                ResultActions perform = this.mockMvc.perform(post(END_POINT_PATH + "/wallet")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content(requestBody));
+                return perform.andExpect(status().isOk());
+            };
+
+            Future<ResultActions> future = executorService.submit(callable);
+            futures.add(future);
+        }
+        for (Future<ResultActions> future : futures) {
+            future.get();
+        }
+
+        BalanceResponse balanceResponse = new BalanceResponse(302000F);
+        String response = objectMapper.writeValueAsString(balanceResponse);
+        this.mockMvc.perform(get(END_POINT_PATH+"/wallets/"+id))
+                .andDo(print())
+                .andExpect(status().isOk())
+                .andExpect(content().json(response));
+    }
 }